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Cover Page - USD ($)	12 Months Ended
Cover Page - USD ($)	Dec. 31, 2019	Feb. 19, 2020	Jun. 30, 2019
Cover page.
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2019
Document Transition Report	false
Entity File Number	001-33497
Entity Registrant Name	Amicus Therapeutics, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	71-0869350
Entity Address, Address Line One	1 Cedar Brook Drive,
Entity Address, City or Town	Cranbury,
Entity Address, State or Province	NJ
Entity Address, Postal Zip Code	08512
City Area Code	(609)
Local Phone Number	662-2000
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	FOLD
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 3,147,432,201
Entity Common Stock, Shares Outstanding		257,244,659
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE: Portions of the Proxy Statement for the registrant's 2020 Annual Meeting of Stockholders which is to be filed subsequent to the date hereof are incorporated by reference into Part III of this Annual Report on Form 10-K.
Entity Central Index Key	0001178879
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 142,837	$ 79,749
Investments in marketable securities	309,903	424,403
Accounts receivable	33,284	21,962
Inventories	14,041	8,390
Prepaid expenses and other current assets	20,008	16,592
Total current assets	520,073	551,096
Operating lease right-of-use assets, less accumulated amortization of $5,342 and $0 at December 31, 2019 and December 31, 2018, respectively	33,315
Property and equipment, less accumulated depreciation of $17,604 and $15,671 at December 31, 2019 and December 31, 2018, respectively	47,705	11,375
In-process research & development	23,000	23,000
Goodwill	197,797	197,797
Other non-current assets	28,317	6,683
Total Assets	850,207	789,951
Current liabilities:
Accounts payable, accrued expenses, and other current liabilities	120,373	80,625
Deferred reimbursements	1,250	5,500
Operating lease liabilities	7,189
Total current liabilities	128,812	86,125
Deferred reimbursements	8,906	10,156
Convertible notes	2,131	175,006
Senior secured term loan	147,374	146,734
Contingent consideration payable	22,681	19,700
Deferred income taxes	5,051	6,465
Operating lease liabilities	53,531
Other non-current liabilities	5,296	2,853
Total Liabilities	373,782	447,039
Commitments and contingencies
Stockholders' equity:
Common stock, $.01 par value, 500,000,000 shares authorized, 255,417,869 and 189,383,924 shares issued and outstanding at December 31, 2019 and December 31, 2018, respectively	2,598	1,942
Additional paid-in capital	2,227,225	1,740,061
Accumulated other comprehensive loss:
Foreign currency translation adjustment	2,785	495
Unrealized gain (loss) on available-for securities	40	(427)
Warrants	12,387	13,063
Accumulated deficit	(1,768,610)	(1,412,222)
Total stockholders' equity	476,425	342,912
Total Liabilities and Stockholders' Equity	$ 850,207	$ 789,951

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Accumulated depreciation and amortization, operating lease right-of-use assets	$ 5,342	$ 0
Accumulated depreciation of property and equipment	$ 17,604	$ 15,671
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	500,000,000	500,000,000
Common stock, shares issued (in shares)	255,417,869	189,383,924
Common stock, shares outstanding (in shares)	255,417,869	189,383,924

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Net product sales	$ 182,237	$ 91,245	$ 36,930
Cost of goods sold	21,963	14,404	6,236
Gross profit	160,274	76,841	30,694
Operating expenses:
Research and development	286,378	270,902	149,310
Selling, general, and administrative	169,861	127,200	88,671
Changes in fair value of contingent consideration payable	3,297	3,300	(234,322)
Loss on impairment of assets	0	0	465,427
Depreciation and amortization	4,775	4,216	3,593
Total operating expenses	464,311	405,618	472,679
Loss from operations	(304,037)	(328,777)	(441,985)
Other income (expenses):
Interest income	10,249	10,461	4,096
Interest expense	(18,872)	(22,402)	(17,240)
Loss on exchange of convertible notes	(40,624)	0	0
Change in fair value of derivatives	0	(2,739)	0
Other (expense) income	(2,626)	(5,632)	6,008
Loss before income tax	(355,910)	(349,089)	(449,121)
Income tax (expense) benefit	(478)	94	165,119
Net loss attributable to common stockholders	$ (356,388)	$ (348,995)	$ (284,002)
Net loss attributable to common stockholders per common share - basic and diluted (in dollars per share)	$ (1.48)	$ (1.88)	$ (1.85)
Weighted-average common shares outstanding - basic and diluted (in shares)	240,421,001	185,790,021	153,355,144

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (356,388)	$ (348,995)	$ (284,002)
Other comprehensive gain (loss):
Foreign currency translation adjustment gain (loss), net of tax impact of $889, $0, and $0, respectively	2,290	2,537	(3,604)
Unrealized gain (loss) on available-for-sale securities, net of tax impact of $182, $0, and $0, respectively	467	9	(538)
Other comprehensive income (loss)	2,757	2,546	(4,142)
Comprehensive loss	$ (353,631)	$ (346,449)	$ (288,144)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Consolidated Statements of Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Foreign currency translation gain (loss), tax impact	$ 889	$ 0	$ 0
Available-for-sale securities, tax expense (benefit)	$ 182	$ 0	$ 0

Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Warrants	Other Comprehensive Gain (Loss)	Accumulated Deficit
Balance (in shares) at Dec. 31, 2016		142,691,986
Balance at Dec. 31, 2016	$ 360,151	$ 1,480	$ 1,120,156	$ 16,076	$ 2,047	$ (779,608)
Increase (Decrease) in Stockholders' Equity
Stock issued from exercise of stock options, net (in shares)		2,878,681
Stock issued from exercise of stock options, net	16,301	$ 29	16,272
Stock issued from equity financing (in shares)		21,122,449
Stock issued from equity financing	243,037	$ 212	242,825
Restricted stock tax vesting (in shares)		296,674
Restricted stock tax vesting	(1,596)		(1,596)
Stock-based compensation	23,101		23,101
Unrealized holding loss on available-for-sale securities	(538)				(538)
Foreign currency translation adjustment	(3,604)				(3,604)
Net loss	(284,002)					(284,002)
Balance (in shares) at Dec. 31, 2017		166,989,790
Balance at Dec. 31, 2017	352,850	$ 1,721	1,400,758	16,076	(2,095)	(1,063,610)
Increase (Decrease) in Stockholders' Equity
Stock issued from exercise of stock options, net (in shares)		1,397,908
Stock issued from exercise of stock options, net	9,144	$ 14	9,130
Stock issued from equity financing (in shares)		20,239,839
Stock issued from equity financing	294,583	$ 202	294,381
Restricted stock tax vesting (in shares)		303,173
Restricted stock tax vesting	(2,832)		(2,832)
Stock-based compensation	29,260		29,260
Reclassification upon ASU 2018-02 adoption					(383)	383
Warrants exercised (in shares)		453,214
Warrants exercised	3,617	$ 5	6,625	(3,013)
Change in fair value of derivatives	2,739		2,739
Unrealized holding loss on available-for-sale securities	9				9
Foreign currency translation adjustment	2,537				2,537
Net loss	$ (348,995)					(348,995)
Balance (in shares) at Dec. 31, 2018	189,383,924	189,383,924
Balance at Dec. 31, 2018	$ 342,912	$ 1,942	1,740,061	13,063	68	(1,412,222)
Increase (Decrease) in Stockholders' Equity
Stock issued from exercise of stock options, net (in shares)		1,967,087
Stock issued from exercise of stock options, net	11,476	$ 20	11,456
Stock issued from equity financing (in shares)		18,720,930
Stock issued from equity financing	188,994	$ 187	188,807
Restricted stock tax vesting (in shares)		477,198
Restricted stock tax vesting	(3,235)		(3,235)
Stock issued for contingent consideration (in shares)		771,804
Stock issued for contingent consideration	9,316	$ 8	9,308
Stock-based compensation	44,430
Warrants exercised (in shares)		101,787
Warrants exercised	812	$ 1	1,487	(676)
Equity component of the convertible notes (in shares)		43,995,139
Equity component of the convertible notes	215,476	$ 440	215,036
Termination of capped call confirmations	19,875		19,875
Unrealized holding loss on available-for-sale securities	467				467
Foreign currency translation adjustment	2,290				2,290
Net loss	$ (356,388)					(356,388)
Balance (in shares) at Dec. 31, 2019	255,417,869	255,417,869
Balance at Dec. 31, 2019	$ 476,425	$ 2,598	$ 2,227,225	$ 12,387	$ 2,825	$ (1,768,610)

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities
Net loss	$ (356,388)	$ (348,995)	$ (284,002)
Adjustments to reconcile net loss to net cash used in operating activities:
Amortization of debt discount and deferred financing	2,546	10,976	9,703
Depreciation and amortization	4,775	4,216	3,593
Stock-based compensation	44,430	29,260	23,101
Loss on exchange of convertible debt	40,624	0	0
Change in fair value of derivatives	0	2,739	(265)
Non-cash changes in the fair value of contingent consideration payable	3,297	3,300	(234,322)
Foreign currency remeasurement (gain) loss	254	3,217	(5,620)
Non-cash deferred taxes	(1,415)	0	(167,305)
Loss on impairment	0	0	465,427
Other	(149)	59	(8)
Changes in operating assets and liabilities:
Accounts receivable	(11,114)	(13,294)	(7,725)
Inventories	(5,114)	(4,205)	(897)
Prepaid expenses and other current assets	(3,287)	2,488	(15,329)
Accounts payable, accrued expenses, and other current liabilities	46,742	17,115	12,563
Other non-current assets and liabilities	(10,117)	(581)	(9)
Deferred reimbursements	(5,500)	(6,250)	(12,600)
Net cash used in operating activities	(250,416)	(299,955)	(213,695)
Investing activities
Sale and redemption of marketable securities	499,047	463,502	323,753
Purchases of marketable securities	(383,882)	(578,394)	(490,468)
Capital expenditures	(20,012)	(6,308)	(4,526)
Net cash provided by (used in) investing activities	95,153	(121,200)	(171,241)
Financing activities
Proceeds from issuance of common stock and warrants, net of issuance costs	188,994	294,584	243,037
Payment of finance leases	(420)
Payment of finance leases		(334)	(308)
Purchase of vested restricted stock units	(3,235)	(2,832)	(1,596)
Proceeds from termination of capped call confirmations	19,875	0	0
Proceeds from exercise of stock options	11,476	9,144	16,301
Proceeds from exercise of warrants	812	3,617	0
Payment of contingent consideration	0	0	(10,000)
Proceeds from loan agreements, net of issuance costs	0	146,596	0
Net cash provided by financing activities	217,502	450,775	247,434
Effect of exchange rate changes on cash, cash equivalents, and restricted cash	1,729	1,518	1,326
Net increase (decrease) in cash, cash equivalents, and restricted cash	63,968	31,138	(136,176)
Cash, cash equivalents, and restricted cash at the beginning of the year	82,375	51,237	187,413
Cash, cash equivalents, and restricted cash at the end of the year	146,343	82,375	51,237
Supplemental disclosures of cash flow information
Tenant improvements paid through lease incentive	19,388	0	0
Cash paid during the period for interest	16,966	7,500	7,424
Contingent consideration paid in shares	9,316	0	0
Capital expenditures unpaid at the end of period	$ 1,865	$ 106	$ 0

Description of Business	12 Months Ended
Description of Business	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	Description of Business Amicus Therapeutics, Inc. (the "Company") is a global, patient-dedicated biotechnology company focused on discovering, developing, and delivering novel medicines for rare diseases. The Company has a portfolio of product opportunities led by the novel medicine for Fabry disease that has achieved widespread global approval, a differentiated biologic for Pompe disease in the clinic, and an industry leading rare disease gene therapy portfolio. The cornerstone of the Company’s portfolio is Galafold^® (also referred to as "migalastat"), the first and only approved oral precision medicine for people living with Fabry disease who have amenable genetic variants. Migalastat is currently approved under the trade name Galafold^® in the United States ("U.S."), European Union ("E.U."), United Kingdom ("U.K."), and Japan, with multiple additional approvals granted and applications pending in several other geographies around the world. The lead biologics program of the Company’s pipeline is Amicus Therapeutics GAA ("AT-GAA", also known as ATB200/AT2221), a novel, clinical-stage, potential best-in-class treatment paradigm for Pompe disease. In February 2019, the U.S. Food and Drug Administration ("FDA") granted Breakthrough Therapy designation to AT-GAA for the treatment of late onset Pompe disease. In the first quarter of 2020, the British Medicines and Healthcare Products Regulatory Agency issued a Promising Innovative Medicine designation for AT-GAA for the treatment of late-onset Pompe disease. The Company has established an industry leading gene therapy portfolio of potential therapies for people living with rare metabolic diseases, through a license with Nationwide Children's Hospital ("NCH") and an expanded collaboration with the University of Pennsylvania ("Penn"). The Company's pipeline includes gene therapy programs in rare, neurologic lysosomal disorders ("LDs"), specifically: CLN6, CLN3, CLN8 and CLN1 Batten disease, Pompe disease, Fabry disease, CDKL5 deficiency disorder ("CDD"), Niemann-Pick Type C ("NPC"), Mucopolysaccharidosis Type IIIB ("MPSIIIB"), as well as a next generation program in Mucopolysaccharidosis Type IIIA ("MPSIIIA"). This expanded collaboration with Penn also provides the Company with exclusive disease-specific access and option rights to develop potentially disruptive new gene therapy platform technologies and programs for most LDs and a broader portfolio of more prevalent rare diseases, including Rett Syndrome, Angelman Syndrome, Myotonic Dystrophy, and select other muscular dystrophies. For additional information, see "— Note 16. Collaboration Agreement." During the second quarter of 2019, the Company completed an underwritten equity offering and issued 18.7 million shares of its common stock at $10.75 per share, inclusive of the fully exercised option to purchase additional shares from the initial offering. This transaction resulted in net proceeds of $189.0 million, after deducting underwriting discounts and commissions and offering expenses. During the first and second quarters of 2019, the Company entered into separate, privately negotiated exchange agreements (the "Exchange Agreements") with a limited number of holders (the "Holders") of the unsecured Convertible Senior Notes due in 2023 ("Convertible Notes"). Under the terms of the Exchange Agreements, the Holders agreed to exchange an aggregate principal amount of $247.2 million of Convertible Notes held by them in exchange for an aggregate of approximately 44.0 million shares of the Company's common stock, par value $0.01 per share. For additional information, see "— Note 12. Debt." The Company had an accumulated deficit of approximately $1.8 billion as of December 31, 2019 and anticipates incurring losses through the fiscal year ending December 31, 2020 and beyond. The Company has historically funded its operations through stock offerings, debt issuances, Galafold^® revenues, collaborations, and other financing arrangements. The current cash position, including expected Galafold^® revenues, is sufficient to fund ongoing Fabry, Pompe, and gene therapy program operations into the first half of 2022. Potential future business development collaborations, pipeline expansion, and investment in manufacturing capabilities could impact the Company's future capital requirements.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Basis of Presentation

The Company has prepared the accompanying Consolidated Financial Statements in accordance with U.S. generally accepted accounting principles ("U.S. GAAP") and include all adjustments necessary for the fair presentation of the Company's financial position for the periods presented.

Consolidation

The Consolidated Financial Statements include the accounts of the Company and its subsidiaries. Intercompany accounts and transactions are eliminated in consolidation.

Foreign Currency Transactions

The functional currency for most of the Company's foreign subsidiaries is their local currency. For non-U.S. subsidiaries that transact in a functional currency other than the U.S. dollar, assets and liabilities are translated at current rates of exchange at the balance sheet date. Income and expense items are translated at the average foreign exchange rates for the period. Adjustments resulting from the translation of the financial statements of the Company's foreign operations into U.S. dollars are excluded from the determination of net income and are recorded in accumulated other comprehensive income, a separate component of stockholders' equity.

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting periods. Actual results could differ from those estimates.

Cash, Cash Equivalents, Marketable Securities, and Restricted Cash

The Company considers all highly liquid investments purchased with a maturity of three months or less at the date of acquisition, to be cash equivalents. Marketable securities consist of fixed income investments with a maturity of greater than three months and other highly liquid investments that can be readily purchased or sold using established markets. These investments are classified as available-for-sale and are reported at fair value on the Company’s Consolidated Balance Sheets. Unrealized holding gains and losses are reported within comprehensive income (loss) in the Statements of Comprehensive Loss. Fair value is based on available market information including quoted market prices, broker or dealer quotations or other observable inputs.

Restricted cash consists primarily of funds held to satisfy the requirements of certain agreements that are restricted in their use and is included in non-current assets on the Company’s Consolidated Balance Sheets.

Concentration of Credit Risk

The Company's financial instruments that are exposed to concentration of credit risk consist primarily of cash, cash equivalents, and marketable securities. The Company maintains its cash and cash equivalents in bank accounts, which, at times, exceed federally insured limits. The Company invests its marketable securities in high-quality commercial financial instruments. The Company has not recognized any losses from credit risks on such accounts during any of the periods presented. The Company believes it is not exposed to significant credit risk on its cash, cash equivalents, or marketable securities.

The Company is subject to credit risk from its accounts receivable related to its product sales of Galafold^®. The Company's accounts receivable at December 31, 2019 have arisen from product sales primarily in Europe and the U.S. The Company will periodically assess the financial strength of its customers to establish allowances for anticipated losses, if any. For accounts receivable that have arisen from named patient sales, the payment terms are predetermined, and the Company evaluates the creditworthiness of each customer on a regular basis. As of December 31, 2019, the Company recorded an allowance for doubtful accounts of $0.1 million.

Property and Equipment

Property and equipment are stated at cost, less accumulated depreciation. Depreciation is calculated over the estimated useful lives of the respective assets, which range from three to five years, or the lesser of the related initial term of the lease or useful life for leasehold improvements.

The initial cost of property and equipment consists of its purchase price and any directly attributable costs of bringing the asset to its working condition and location for its intended use. Expenditures incurred after the fixed assets have been put into operation, such as repairs and maintenance, are charged to income in the period in which the costs are incurred. Major replacements, improvements, and additions are capitalized in accordance with Company policy.

Revenue Recognition

The Company’s net product sales consist of sales of Galafold^® for the treatment of Fabry disease. The Company has recorded revenue on sales where Galafold^® is available either on a commercial basis or through a reimbursed early access program ("EAP"). Orders for Galafold^® are generally received from distributors and pharmacies, with the ultimate payor often a government authority. In 2019, one customer accounted for 22% of net product sales and 11% of accounts receivable from product sales.

The Company recognizes revenue when its performance obligations to its customers have been satisfied, which occurs at a point in time when the pharmacies or distributors obtain control of Galafold^®. The transaction price is determined based on fixed consideration in the Company’s customer contracts and is recorded net of estimates for variable consideration, which are third-party discounts and rebates. The identified variable consideration is recorded as a reduction of revenue at the time revenues from sales of Galafold^® are recognized. The Company recognizes revenue to the extent that it is probable that a significant revenue reversal will not occur in a future period. These estimates may differ from actual consideration received. The Company evaluates these estimates each reporting period to reflect known changes.

The following table summarizes the Company's net product sales from Galafold^® disaggregated by geographic area:



	For the Year
(in thousands)	2019		2018		2017
U.S.	$	52,478	$	7,223	$	—
Ex-U.S.	129,759		84,022		36,930
Total net product sales	$	182,237	$	91,245	$	36,930

Inventories and Cost of Goods Sold

Inventories are stated at the lower of cost and net realizable value, determined by the first-in, first-out method. Inventories are reviewed periodically to identify slow-moving or obsolete inventory based on projected sales activity as well as product shelf-life. In evaluating the recoverability of inventories produced, the probability that revenue will be obtained from the future sale of the related inventory is considered and inventory value is written down for inventory quantities in excess of expected requirements. Expired inventory is disposed of and the related costs are recognized as cost of product sales in the Consolidated Statements of Operations.

Cost of goods sold includes the cost of inventory sold, manufacturing and supply chain costs, product shipping and handling costs, provisions for excess and obsolete inventory, as well as royalties payable.

Fair Value Measurements

The Company records certain asset and liability balances under the fair value measurements as defined by the FASB guidance. Current FASB fair value guidance emphasizes that fair value is a market-based measurement, not an entity-specific measurement. Therefore, a fair value measurement should be determined based on the assumptions that market participants would use in pricing the asset or liability. As a basis for considering market participant assumptions in fair value measurements, current FASB guidance establishes a fair value hierarchy that distinguishes between market participant assumptions based on market data obtained from sources independent of the reporting entity (observable inputs that are classified within Levels 1 and 2 of the hierarchy) and the reporting entity's own assumptions that market participants assumptions would use in pricing assets or liabilities (unobservable inputs classified within Level 3 of the hierarchy).

Level 1 inputs utilize quoted prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access at measurement date. Level 2 inputs are inputs other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly. Level 2 inputs may include quoted prices for similar assets and liabilities in active markets, as well as inputs that are observable for the asset or liability (other than quoted prices), such as interest rates, foreign exchange rates, and yield curves that are observable at commonly quoted intervals. Level 3 inputs are unobservable inputs for the asset or liability, which is typically based on an entity's own assumptions, as there is little, if any, related market activity. In instances where the determination of the fair value measurement is based on inputs from different levels of the fair value hierarchy, the level in the fair value hierarchy within which the entire fair value measurement falls is based on the lowest level input that is significant to the fair value measurement in its entirety. The Company's assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment and considers factors specific to the asset or liability.

Contingent Liabilities

On an ongoing basis, the Company may be involved in various claims and legal proceedings. On a quarterly basis, the Company reviews the status of each significant matter and assesses its potential financial exposure. If the potential loss from any claim, asserted or unasserted, or legal proceeding is considered probable and the amount can be reasonably estimated, the Company will accrue a liability for the estimated loss. Because of uncertainties related to claims and litigation, accruals will be based on the Company's best estimates based on available information. On a periodic basis, as additional information becomes available, or based on specific events such as the outcome of litigation or settlement of claims, the Company may reassess the potential liability related to these matters and may revise these estimates, which could result in material adverse adjustments to the Company's operating results.

Research and Development Costs

Research and development costs are expensed as incurred. Research and development expense consist primarily of costs related to personnel, including salaries and other personnel related expenses, consulting fees, and the cost of facilities and support services used in drug development. Assets acquired that are used for research and development and have no future alternative use are expensed as in-process research and development.

Interest Income and Interest Expense

Interest income consists of interest earned on the Company's cash, cash equivalents, and marketable securities. Interest expense consists of interest incurred on debt and finance leases.

Income Taxes

The Company accounts for income taxes under the liability method. Under this method deferred income tax liabilities and assets are determined based on the difference between the financial statement carrying amounts and tax basis of assets and liabilities and for operating losses and tax credit carry forwards, using enacted tax rates in effect in the years in which the differences are expected to reverse. A valuation allowance is recorded if it is "more likely than not" that a portion or all of a deferred tax asset will not be realized.

Other Comprehensive Income (Loss)

Components of other comprehensive income (loss) include unrealized gains and losses on available-for-sale securities and gain (loss) on foreign currency transactions and are included in the Statements of Comprehensive Loss.

Leases

The Company primarily enters into lease agreements for office space, equipment, and vehicles. The leases have varying terms, some of which could include options to renew, extend, and early terminate. The Company determines if an arrangement is a lease at contract inception. Operating leases are included in right-of-use ("ROU") assets and lease liabilities on the Consolidated Balance Sheets.

ROU assets represent the Company's right to control the use of an explicitly or implicitly identified fixed asset for a period of time and lease liabilities represent the Company's obligation to make lease payments arising from the lease. Control of an underlying asset is conveyed to the Company if the Company obtains the rights to direct the use of and to obtain substantially all of the economic benefits from using the underlying asset. ROU assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. The Company uses its incremental borrowing rate based on the information available at commencement date in determining the present value of lease payments.

Lease payments included in the measurement of the lease liability are comprised of fixed payments. Variable lease payments are excluded from the ROU asset and lease liability and are recognized in the period in which the obligation for those payments is incurred. Variable lease payments are presented in the Consolidated Statements of Operations in the same line item as expenses arising from fixed lease payments for operating leases. The Company has lease agreements that include lease and non-lease components, which the Company accounts for as a single lease component for all underlying asset categories.

The lease term for all of the Company's leases include the non-cancellable period of the lease plus any additional periods covered by either a Company option to extend (or not to terminate) the lease that the Company is reasonably certain to exercise, or an option to extend (or not to terminate) the lease controlled by the lessor.

Leases with an initial term of 12 months or less are not recorded on the Consolidated Balance Sheets. The Company recognizes lease expense for these leases on a straight-line basis over the lease term. The Company applies this policy to all underlying asset categories.

The information presented for the periods prior to January 1, 2019 has not been restated and is reported under the accounting standard in effect for those periods. For additional information, see " -Note 13. Leases" and "-Note 2. Summary of Significant Accounting Policies, Recent Accounting Developments - Guidance Adopted in 2019."

Nonqualified Cash Deferral Plan

The Company's Cash Deferral Plan (the "Deferral Plan"), provides certain key employees and members of the Board of Directors as selected by the Compensation Committee of the Board of Directors of the Company (the "Compensation Committee"), with an opportunity to defer the receipt of such participant's base salary, bonus, and director's fees, as applicable. The Deferral Plan is intended to be a nonqualified deferred compensation plan that complies with the provisions of Section 409A of the Internal Revenue Code (the "Code"). All of the investments held in the Deferral Plan are classified as investments held-to-maturity and recorded at fair value with changes in the investments' fair value recognized as earnings in the period they occur. The corresponding liability for the Deferral Plan is included in other non-current liability in the Consolidated Balance Sheets.

Equity-based Compensation

At December 31, 2019, the Company had three equity-based employee compensation plans, which are described more fully in "— Note 9. Stockholders' Equity." The Company applies the fair value method of measuring equity-based compensation, which requires a public entity to measure the cost of employee services received in exchange for an award of equity instruments based on the grant-date fair value of the award.

Loss per Common Share

The Company calculates net loss per share as a measurement of the Company's performance while giving effect to all dilutive potential common shares that were outstanding during the reporting period. The Company had a net loss for all periods presented; accordingly, the inclusion of common stock options, unvested RSUs, and warrants would be anti-dilutive. Therefore, the weighted average shares used to calculate both basic and diluted earnings per share are the same. See "— Note 17. Basic and Diluted Net Loss per Common Share" for further discussion on net loss per share.

Segment Information

The Company currently operates in one business segment focused on the discovery, development, and commercialization of advanced therapies to treat a range of devastating rare and orphan diseases. The Company is not organized by market and is managed and operated as one business. A single management team reports to the chief operating decision maker who comprehensively manages the entire business. The Company does not operate any separate lines of business or separate business entities with respect to its products. Accordingly, the Company does not accumulate discrete financial information with respect to separate service lines, and thus there is one reporting unit.

Business Combinations

The Company assigns fair value to the tangible and intangible assets acquired and liabilities assumed based upon their estimated fair values on the acquisition date from acquired businesses. The purchase price allocation process requires management to make significant estimates and assumptions, especially at the acquisition date with respect to intangible assets and in-process research and development ("IPR&D"). In connection with the purchase price allocations for acquisitions, the Company estimates the fair value of contingent payments utilizing a probability-based income approach inclusive of an estimated discount rate.

Contingent Consideration Payable

Contingent consideration payments in asset acquisitions are recognized when the contingency is resolved and the consideration is paid or becomes payable. This does not apply in circumstances when the contingent consideration meets the definition of a derivative, in which case the amount becomes part of the basis in the asset acquired. Upon recognition of the contingent consideration payment, the amount is included in the cost of the acquired asset or group of assets. The Company determines the fair value of contingent acquisition consideration payable on the acquisition date using a probability-based income approach utilizing an appropriate discount rate. Contingent acquisition consideration payable is shown as a non-current liability on the Company's Consolidated Balance Sheets. The fair value of the contingent consideration payable will be determined each period end and the resulting change will be recorded on the Consolidated Statements of Operations.

Intangible Assets and Goodwill

The Company records goodwill in a business combination when the total consideration exceeds the fair value of the net tangible and identifiable intangible assets acquired. Purchased IPR&D is accounted for as an indefinite lived intangible asset until the underlying project is completed, at which point the intangible asset will be accounted for as a definite lived intangible asset, or abandoned, at which point the intangible asset will be written off or partially impaired. Goodwill and indefinite lived intangible assets are assessed annually for impairment and whenever events or circumstances indicate that the carrying amount of an asset may not be recoverable. If it is determined that the full carrying amount of an asset is not recoverable, an impairment loss is recorded in the amount by which the carrying amount of the asset exceeds its fair value. No indicators of impairment were noted during the years ended December 31, 2019 and December 31, 2018.

Recent Accounting Developments - Guidance Adopted in 2019

ASU 2016-02 - In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) ("ASU 2016-02"). ASU 2016-02 requires the recognition of lease assets and lease liabilities on the balance sheet for all lease obligations and disclosing key information about leasing arrangements. ASU 2016-02 requires the recognition of lease assets and lease liabilities by lessees for those leases classified as operating leases under previous generally accepted accounting principles. In August 2018, the FASB issued ASU 2018-11, Leases (Topic 842): Targeted Improvements, ("ASU 2018-11"). ASU 2018-11 provided entities with an additional transition method for adoption, whereby, an entity initially applies the new leases standard at the adoption date and recognizes a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. Effective January 1, 2019 the Company adopted ASU 2016-02, along with the amendments issued in 2017 and 2018, and elected the transition method in ASU 2018-11. The Company elected the package of transition provisions available for expired or existing contracts, which allowed the Company to carry forward its historical assessments of (i) whether contracts are or contain leases, (ii) lease classification and (iii) initial direct costs. In addition, the Company applied the short-term lease recognition exemption for leases with terms at inception not greater than 12 months and will apply the practical expedient not to separate lease and non-lease components for new and modified leases commencing after adoption. The information presented for the periods prior to January 1, 2019 has not been restated and is reported under the accounting standard in effect for those periods. Upon adoption, the Company recorded a lease liability with a corresponding right-of-use asset of $17.6 million. The adoption did not have a material impact on the Consolidated Statements of Operations and the Consolidated Statements of Cash Flows.

Recent Accounting Developments - Guidance Not Yet Adopted

ASU 2019-12 - In December 2019, the FASB issued ASU 2019-15, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes ("ASU 2019-12"). This new guidance removes specific exceptions to the general principles in Topic 740. It eliminates the need for an organization to analyze whether the following apply in a given period: (i) exception to the incremental approach for intraperiod tax allocation; (ii) exceptions to accounting for basis differences when there are ownership changes in foreign investments; and (iii) exception in interim period income tax accounting for year-to-date losses that exceed anticipated losses. ASU 2019-12 also improves financial statement preparers’ application of income tax-related guidance and simplifies the following: (i) franchise taxes that are partially based on income; (ii) transactions with a government that result in a step up in the tax basis of goodwill; (iii) separate financial statements of legal entities that are not subject to tax; and (iv) enacted changes in tax laws in interim periods. ASU 2019 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. Early adoption is permitted for public business entities for periods for which financial statements have not yet been issued. An entity that elects early adoption in an interim period should reflect any adjustments as of the beginning of the annual period that includes that interim period. Additionally, an entity that elects early adoption should adopt all the amendments in the same period. The Company is currently assessing the impact that this standard will have on its Consolidated Financial Statements upon adoption.

ASU 2018-15 - In August 2018, the FASB issued ASU 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): ("ASU 2018-15"), relating to a customer’s accounting for implementation, set-up, and other upfront costs incurred in a cloud computing arrangement that is hosted by a vendor. Under the new guidance, a customer will apply the same criteria for capitalizing implementation costs as it would for an arrangement that has a software license. The new guidance does not affect the accounting for the service element of a hosting arrangement that is a service contract. The new guidance also prescribes the balance sheet, income statement and cash flow classification of the capitalized software costs and related amortization expense and requires additional quantitative and qualitative disclosures. ASU 2018-15 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019 for public companies. The Company will adopt this guidance prospectively on January 1, 2020, and it believes the adoption of this guidance will not have a material impact on its Consolidated Financial Statements or related disclosures.

ASU 2018-13 - In August 2018, the FASB issued ASU 2018-03, Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement ("ASU 2018-13"). The amendments modify the disclosure requirements in Topic 820. ASU 2018-13 is effective for all entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. The amendments on (i) changes in unrealized gains and losses, (ii) the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements, and (iii) the narrative description of measurement uncertainty should be applied prospectively for only the most recent interim or annual period presented in the initial fiscal year of adoption. All other amendments should be applied retrospectively to all periods presented upon their effective date. The Company will adopt this guidance on January 1, 2020, and it believes the adoption of this guidance will not have a material impact on its Consolidated Financial Statements or related disclosures.

ASU 2017-04 - In January 2017, the FASB issued ASU 2017-04, Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment ("ASU 2017-04"). ASU 2017-04 simplifies the recognition and measurement of a goodwill impairment loss by eliminating Step 2 of the quantitative goodwill impairment test. The guidance requires a one-step impairment test in which an entity compares the fair value of a reporting unit with its carrying amount and recognizes an impairment charge for the amount by which the carrying amount exceeds the reporting unit's fair value, if any. ASU 2017-04 is effective for fiscal years beginning after December 15, 2019 and should be applied on a prospective basis. The Company will adopt this guidance on January 1, 2020, and it believes the adoption of this guidance will not have a material impact on its Consolidated Financial Statements or related disclosures.

ASU 2016-13 - In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments ("ASU 2016-13"). ASU 2016-13 requires financial assets measured at amortized cost basis to be presented at the net amount expected to be collected and amends guidance on the impairment of financial instruments. ASU 2016-13 is effective for public companies who are SEC filers for fiscal years beginning after December 15, 2019, including interim periods within those years. The Company will adopt this guidance on January 1, 2020, and it believes the adoption of this guidance will not have a material impact on its Consolidated Financial Statements or related disclosures.

Acquisitions	12 Months Ended
Acquisitions	Dec. 31, 2019
Business Combinations [Abstract]
Acquisitions	Acquisitions Acquisition of Celenex In September 2018, the Company expanded its pipeline by acquiring the rights and related intellectual property of ten gene therapy programs through its acquisition of Celenex, Inc., ("Celenex"). Celenex is a private, clinical stage gene therapy company whose lead programs are ten gene therapy programs including CLN6 and CLN3, which are in clinical stage, and several programs in pre-clinical stage. Pursuant to the terms of the agreement, the Company acquired Celenex for cash consideration of $100 million. The Company has also agreed to pay up to an additional $15 million in connection with the achievement of certain development milestones, $262 million in connection with the achievement of certain regulatory approval milestones across multiple programs and up to $75 million in tiered sales milestone payments. Celenex has an exclusive license agreement with Nationwide Children’s Hospital ("NCH"). Under this license agreement, NCH is eligible to receive development and sales-based milestones of up to $7.8 million for each product. The Company evaluated the Celenex transaction and concluded that the transaction did not meet the definition of a business and was an asset acquisition. Given the fact that the license has no alternative future use, the $100.0 million upfront payment was expensed to research and development expense in the Consolidated Statements of Operations for the year ended December 31, 2018. Acquisition of MiaMed, Inc. In July 2016, the Company entered into an Agreement and Plan of Merger (the "MiaMed Agreement") with MiaMed, Inc., ("MiaMed"). MiaMed is a pre-clinical biotechnology company focused on developing protein replacement therapy for CDD and related diseases. Under the terms of the MiaMed Agreement, the former holders of MiaMed's capital stock received an aggregate of $6.5 million, comprised of (i) approximately $1.8 million in cash (plus MiaMed's cash and cash equivalents at closing and less any of MiaMed's unpaid third-party fees and expenses related to the transaction), and (ii) 825,603 shares of the Company's common stock. In addition, the Company also agreed to pay up to an additional $83.0 million in connection with the achievement of certain clinical, regulatory, and commercial milestones, for a potential aggregate deal value of $89.5 million. The Company evaluated the transaction and concluded that it only acquired inputs and did not acquire any processes. The Company will need to develop its own processes in order to produce an output. Therefore, the Company accounted for the transaction as an asset acquisition and accordingly $6.5 million was expensed to research and development expense in the Consolidated Statements of Operation for the year ended December 31, 2016. Acquisition of Scioderm, Inc. In September 2015, the Company acquired Scioderm Inc., ("Scioderm"), a privately-held biopharmaceutical company focused on developing innovative therapies for treating the rare disease, Epidermolysis Bullosa ("EB"). The acquisition potentially leveraged the Scioderm development team's EB expertise with the Company's global clinical infrastructure to advance SD-101toward regulatory approvals and the Company's commercial, patient advocacy, and medical affairs infrastructure to support a successful global launch. The acquisition of Scioderm was accounted for as a purchase of a business in accordance with ASC 805 Business Combinations. At the end of the first quarter of 2017, the Company achieved 100% enrollment in the Phase 3 clinical study of SD-101 and the milestone payment of $10 million due for this event, was paid in April 2017. On September 13, 2017, the Company reported that top-line data from the randomized, double-blind, placebo-controlled Phase 3 clinical study ("ESSENCE, SD-5") to assess the efficacy and safety of the novel topical wound-healing agent SD-101 did not meet the primary endpoints or secondary endpoints in participants with EB. Based on these top-line data, the Company has no current plans to invest in any additional clinical studies or commercial preparation activities for SD-101. This event led the Company to assess the carrying amount of the program's tangible and intangible assets against their respective fair values. Based on the assessment, the Company recognized a loss on impairment of intangible assets in the amount of $463.7 million and $1.7 million in fixed assets recorded within loss on impairment of assets within the Consolidated Statements of Operations. Since the study did not meet the primary and secondary endpoints, the Company concluded that they will not make the potential milestone payments indicated in the Asset Purchase Agreement to the former Scioderm holders. Accordingly, the Company recognized a gain of $254.7 million in changes in fair value of contingent consideration payable in the third quarter of 2017, in order to decrease the liability to zero. The Company also recognized $0.4 million in selling, general, and administrative costs and $8.1 million in research and development expenses related to the wind-down of operations for the Phase 3 ESSENCE study and ongoing extension studies SD-004 and SD-006, as well as income tax benefit of $164.7 million due to the reduction of the deferred tax liability related to Scioderm IPR&D, in the Consolidated Statements of Operations in the third quarter of 2017. Acquisition of Callidus Biopharma, Inc. In November 2013, the Company acquired Callidus Biopharma, Inc., ("Callidus"), a privately-held biologics company focused on developing best-in-class ERTs for LDs with its lead ERT ATB200 for Pompe disease in late preclinical development. The fair value of the contingent acquisition consideration payments was estimated by applying a probability-based income approach utilizing an appropriate discount rate. Key assumptions include discount rate and various probability factors. This estimation was based on significant inputs that are not observable in the market, referred to as Level 3 inputs. Some of the more significant assumptions used in the valuation include (i) the probability and timing related to the achievement of certain developmental milestones and (ii) and the discount rate. See "— Note 11. Assets and Liabilities Measured at Fair Value", for additional discussion regarding fair value measurements of the contingent acquisition consideration payable. The Company determined the fair value of the contingent consideration to be $22.7 million at December 31, 2019, which is payable beyond the next twelve months, resulting in an increase in the contingent consideration payable and related expense of $3.3 million in the year ended December 31, 2019. The expense is recorded in the Consolidated Statement of Operations within the changes in fair value of contingent consideration line item. During the fourth quarter of 2018, the Company reached a clinical milestone for Callidus, which was the dosing of the first patient in a Phase 3 study. The milestone payment for this event was $9.0 million which was paid in the Company's stock during the first quarter of 2019. For further information, see "— Note 4. Goodwill and Intangible Assets."

Goodwill and Intangible Assets

12 Months Ended

Dec. 31, 2019

Goodwill and Intangible Assets Disclosure [Abstract]

Goodwill and Intangible Assets

In connection with the acquisitions, the Company initially recognized IPR&D of $486.7 million and goodwill of $197.8 million. Intangible assets related to IPR&D assets are considered to be indefinite-lived until the completion or abandonment of the associated research and development efforts. During the period the assets are considered indefinite-lived, they will not be amortized but will be tested for impairment on an annual basis and between annual tests if the Company becomes aware of any events occurring or changes in circumstances that would indicate a reduction in the fair value of the IPR&D assets below their respective carrying amounts.

Goodwill and intangible assets are assessed annually for impairment on October 1 and whenever events or circumstances indicate that the carrying amount of an asset may not be recoverable. If it is determined that the full carrying amount of an asset is not recoverable, an impairment loss is recorded in the amount by which the carrying amount of the asset exceeds its fair value.

As discussed in "— Note 3. Acquisitions", in September 2017, the Company reported that top-line data from the randomized, double-blind, placebo-controlled Phase 3 clinical study ("ESSENCE, SD-005") to assess the efficacy and safety of the novel topical wound-healing agent SD-101 did not meet the primary endpoints or secondary endpoints in participants with EB. This event led to an assessment to determine if an impairment had occurred for goodwill and IPR&D. Based on tests for impairment, the Company determined that IPR&D had been impaired, however goodwill was not impaired based on qualitative and market capitalization tests performed. The loss on impairment of IPR&D of $463.7 million was recorded within loss on impairment of assets in the Consolidated Statements of Operations for the year ended December 31, 2017.

The following table represents the changes in IPR&D for the years ended December 31, 2019 and 2018, respectively:



	(in millions)
Balance at December 31, 2017	$	23.0
Change in IPR&D	—
Balance at December 31, 2018	$	23.0
Change in IPR&D	—
Balance at December 31, 2019	$	23.0

The following table represents the changes in Goodwill for the years ended December 31, 2019 and 2018, respectively:



	(in millions)
Balance at December 31, 2017	$	197.8
Change in goodwill	—
Balance at December 31, 2018	$	197.8
Change in goodwill	—
Balance at December 31, 2019	$	197.8

Cash, Cash Equivalents, Marketable Securities, and Restricted Cash

12 Months Ended

Dec. 31, 2019

Cash, Cash Equivalents, and Short-term Investments [Abstract]

Cash, Cash Equivalents, Marketable Securities, and Restricted Cash

As of December 31, 2019, the Company held $142.8 million in cash and cash equivalents and $309.9 million of available- for-sale debt securities which are reported at fair value on the Company’s Consolidated Balance Sheets. Unrealized holding gains and losses are reported within accumulated other comprehensive loss in the Statements of Comprehensive Loss. If a decline in the fair value of a marketable security below the Company’s cost basis is determined to be other than temporary, such marketable security is written down to its estimated fair value as a new cost basis and the amount of the write-down is included in earnings as an impairment charge.

The Company regularly invests excess operating cash in deposits with major financial institutions, money market funds, notes issued by the U.S. government, as well as fixed income investments and U.S. bond funds, both of which can be readily purchased and sold using established markets. The Company believes that the market risk arising from its holdings of these financial instruments is mitigated as many of these securities are either government backed or of the highest credit rating. Investments that have original maturities greater than three months but less than one year are classified as current.

Cash, cash equivalents, and marketable securities are classified as current unless mentioned otherwise below and consisted of the following:



	As of December 31, 2019
(in thousands)	Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Cash and cash equivalents	$	142,837	$	—	$	—		$	142,837
Corporate debt securities	145,875		121		(5		)	145,991
Commercial paper	73,659		53		(2		)	73,710
Asset-backed securities	77,731		79		—			77,810
U.S. government agency bonds	11,999		2		(10		)	11,991
Money market	350		—		—			350
Certificates of deposit	51		—		—			51
	$	452,502	$	255	$	(17	)	$	452,740
Included in cash and cash equivalents	$	142,837	$	—	$	—		$	142,837
Included in marketable securities ⁽¹⁾	309,665		255		(17		)	309,903
Total cash, cash equivalents, and marketable securities	$	452,502	$	255	$	(17	)	$	452,740

______________________________

⁽¹⁾As of December 31, 2019, $9.5 million of marketable securities have maturity dates greater than 12 months and are available to convert into cash, if needed.



	As of December 31, 2018
(in thousands)	Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Cash and cash equivalents	$	79,749	$	—	$	—		$	79,749
Corporate debt securities	240,969		7		(250		)	240,726
Commercial paper	115,245		—		(104		)	115,141
Asset-backed securities	68,215		4		(84		)	68,135
Money market	350		—		—			350
Certificates of deposit	51		—		—			51
	$	504,579	$	11	$	(438	)	$	504,152
Included in cash and cash equivalents	$	79,749	$	—	$	—		$	79,749
Included in marketable securities	424,830		11		(438		)	424,403
Total cash, cash equivalents, and marketable securities	$	504,579	$	11	$	(438	)	$	504,152

For the year ended December 31, 2019 there were no realized gains or losses. For the fiscal year ended December 31, 2018, there were nominal realized gains. The cost of securities sold is based on the specific identification method.

Unrealized loss positions in the available-for-sale debt securities as of December 31, 2019 and 2018 reflect temporary impairments that have been in a loss position for less than twelve months and as such are recognized in other comprehensive gain (loss). The fair value of these available-for-sale debt securities in unrealized loss positions was $42.6 million and $403.1 million as of December 31, 2019 and 2018, respectively.

The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the Consolidated Balance Sheets that sum to the total of the same such amounts shown in the Consolidated Statements of Cash Flows.



(in thousands)	December 31, 2019		December 31, 2018		December 31, 2017
Cash and cash equivalents	$	142,837	$	79,749	$	49,060
Restricted cash	3,506		2,626		2,177
Cash, cash equivalents, and restricted cash shown in the Consolidated Statements of Cash Flows	$	146,343	$	82,375	$	51,237

Inventories

12 Months Ended

Dec. 31, 2019

Inventory Disclosure [Abstract]

Inventories

Inventories consist of raw materials, work in process, and finished goods related to the manufacture of Galafold^®. The following table summarizes the components of inventories:



(in thousands)	December 31, 2019		December 31, 2018
Raw materials	$	6,544	$	1,291
Work-in-process	3,660		3,485
Finished goods	3,837		3,614
Total inventories	$	14,041	$	8,390

The Company recorded a reserve for inventory of $0.2 million as of December 31, 2019 and 2018, respectively.

Property and Equipment

12 Months Ended

Dec. 31, 2019

Property, Plant and Equipment [Abstract]

Property and Equipment

Property and equipment consist of the following:



	December 31,
(in thousands)	2019			2018
Property and equipment consist of the following:
Computer equipment	$	6,185		$	4,691
Computer software	1,607			1,298
Research equipment	14,568			8,445
Furniture and fixtures	5,157			4,876
Leasehold improvements	30,294			7,425
Vehicles	124			209
Land	3,190			—
Construction in progress	4,184			102
Gross property and equipment	65,309			27,046
Less accumulated depreciation	(17,604		)	(15,671		)
Net property and equipment	$	47,705		$	11,375

Depreciation expense was $4.5 million and $4.2 million for the years ended December 31, 2019 and 2018, respectively.

Accounts Payable, Accrued Expenses, and Other Current Liabilities

12 Months Ended

Dec. 31, 2019

Payables and Accruals [Abstract]

Accounts Payable, Accrued Expenses, and Other Current Liabilities

Accounts payable, accrued expenses, and other current liabilities consist of the following:



	December 31,
(in thousands)	2019		2018
Accounts payable	$	21,722	$	6,606
Accrued professional fees	7,832		2,276
Accrued contract manufacturing & contract research costs	17,800		5,890
Accrued compensation and benefits	27,156		21,731
Accrued program fees	17,016		16,674
Accrued royalties	5,196		4,463
Accrued interest	3,679		4,189
Accrued milestones	4,000		9,000
Accrued sales rebates and discounts	5,900		3,636
Accrued taxes	7,300		1,330
Other	2,772		4,830
	$	120,373	$	80,625

Stockholders' Equity	12 Months Ended
Stockholders' Equity	Dec. 31, 2019
Equity [Abstract]
Stockholders' Equity	Stockholders' Equity Common Stock and Warrants As of December 31, 2019, the Company was authorized to issue 500 million shares of common stock. Dividends on common stock will be paid when, and if, declared by the board of directors. Each holder of common stock is entitled to vote on all matters that are appropriate for stockholder voting and is entitled to one vote for each share held. In March 2019, 101,787 warrants were exercised at $7.98 per share of common stock resulting in gross cash proceeds of $0.8 million. As discussed in "— Note 1. Business" during the second quarter of 2019, the Company completed an underwritten equity offering and issued 18.7 million shares of its common stock at $10.75 per share, inclusive of the fully exercised option to purchase additional shares from the initial offering. This transaction resulted in net proceeds of $189.0 million, after deducting underwriting discounts and commissions and offering expenses. As discussed in "— Note 11. Assets and Liabilities Measured at Fair Value", the Company reached a clinical milestone, which was the dosing of the first patient in a Phase 3 study, related to the contingent consideration from the acquisition of Callidus. The milestone for this event was $9.0 million, which was paid in Company common stock in the first quarter of 2019 and resulted in a $9.3 million impact on stockholder's equity. As discussed in ''— Note 12. Debt'', during the first and second quarters of 2019, the Company entered into separate, privately negotiated Exchange Agreements with the Holders of the Convertible Notes. Under the terms of the Exchange Agreements, the Holders agreed to exchange an aggregate principal amount of $247.2 million of Convertible Notes held by them in exchange for an aggregate of approximately 44.0 million shares of Company's common stock, par value $0.01 per share. In February 2018, the Company completed an underwritten offering of 20.2 million shares of its common stock at $15.50 per share, inclusive of the fully exercised option to purchase additional shares from the initial offering. This transaction resulted in net proceeds of $294.6 million, after deducting underwriting discounts and commissions and offering expenses. In April 2018, 453,214 warrants were exercised at $7.98 per share of common stock resulting in gross cash proceeds of $3.6 million. In June 2018, the Company’s stockholders approved an amendment to the Company’s Restated Certificate of Incorporation to increase the number of shares of common stock, par value $0.01 per share, that the Company is authorized to issue from 250 million shares to 500 million shares. In July 2017, the Company completed an underwriting offering of 21.1 million shares of its common stock at $12.25 per share. This transaction resulted in net proceeds of $243.0 million, after deducting underwriting discounts and commissions and offering expenses. Nonqualified Cash Plan The Company's Deferral Plan, (the "Deferral Plan") provides certain key employees and members of the Board of Directors as selected by the Compensation Committee, with an opportunity to defer the receipt of such participant's base salary, bonus, and director's fees, as applicable. The Deferral Plan is intended to be a nonqualified deferred compensation plan that complies with the provisions of Section 409A of the Internal Revenue Code of 1986 as amended. The Company had a deferred compensation investment balance of $4.4 million and $2.7 million as of December 31, 2019 and 2018, respectively, with corresponding approximate amounts of liability. Deferral Plan investment assets are classified as trading securities and are recorded at fair value with changes in the investments' fair value recognized in AOCI in the period they occur. Deferred compensation liability amounts under the Deferral Plan are included in other long-term liabilities. Equity Incentive Plans The Company’s Equity Incentive Plans consist of the Amended and Restated 2007 Equity Incentive Plan (the ‘‘Plan’’) and the 2007 Director Option Plan (the ‘‘2007 Director Plan’’). The Plan provides for the granting of restricted stock and options to purchase common stock in the Company to employees, directors, advisors, and consultants at a price to be determined by the Company’s Board of Directors. The Plan is intended to encourage ownership of stock by employees and consultants of the Company and to provide additional incentives for them to promote the success of the Company’s business. The 2007 Director Plan is intended to promote the recruiting and retention of highly qualified eligible directors and strengthen the commonality of interest between directors and stockholders by encouraging ownership of common stock of the Company. Under the provisions of each plan, no option will have a term in excess of 10 years. The Board of Directors, or its committee, is responsible for determining the individuals to be granted options, the number of options each individual will receive, the option price per share, and the exercise period of each option. Options granted pursuant to the Plan generally vest 25% on the first year anniversary date of grant plus an additional 1/48th for each month thereafter and may be exercised in whole or in part for 100% of the shares vested at any time after the date of grant. Options under the 2007 Director Plan may be granted to new directors upon joining the Board of Directors and vest in the same manner as options under the Plan. In addition, options are granted to independent directors at each annual meeting of stockholders and vest on the date of the annual meeting of stockholders of the Company in the year following the year during which the options were granted. As of December 31, 2019, the Company has reserved up to 10,667,216 shares for issuance under the Plan and the 2007 Director Plan.

Share based Compensation

12 Months Ended

Dec. 31, 2019

Share-based Payment Arrangement [Abstract]

Share based Compensation

The Company’s Equity Incentive Plans consist of the Plan and the 2007 Director Plan. The Plan provides for the granting of restricted stock units and options to purchase common stock in the Company to employees, directors. advisors, and consultants at a price to be determined by the Company’s Board of Directors. The Plan is intended to encourage ownership of stock by employees and consultants of the Company and to provide additional incentives for them to promote the success of the Company’s business. The 2007 Director Plan is intended to promote the recruiting and retention of highly qualified eligible directors and strengthen the commonality of interest between directors and stockholders by encouraging ownership of common stock of the Company. The Board of Directors, or its committee, is responsible for determining the individuals to be granted options, the number of options each individual will receive, the option price per share, and the exercise period of each option.

On December 21, 2018, the Board of Directors of the Company approved an amendment (the "Amendment") to the Plan. The Amendment provides for certain benefits to qualifying Plan Participants who separate from service with the Company due to death, disability or "Retirement" (as such term is defined under the Plan) ("Qualified Participants"). Options granted under the Plan ("Options") to a Qualified Participant shall continue to vest until the 2nd anniversary of the Qualified Participant’s separation and all vested Options held by such Qualified Participant shall remain exercisable until the earlier of the 4th anniversary of the Qualified Participant’s separation or the original expiration date of the Option. Options that are not exercised during this exercise period shall be forfeited. Time-based restricted stock units and restricted stock granted to a Qualified Participant under the Plan that was scheduled to vest within the two year period following the Qualified Participant's separation shall accelerate and be delivered upon such separation. Any time-based restricted stock units or restricted stock that would have vested after such two year period will be forfeited upon the Qualified Participant's separation. Also, per the Amendment, any performance-based restricted stock units under the Plan ("PRSUs") received by the Qualified Participant, shall remain eligible to vest after the Qualified Participant’s separation based on the actual performance of the Company through the end of the performance period applicable to any such PRSU.

Stock Option Grants

The Company uses the fair value method of measuring stock-based compensation, using the fair value of each equity award granted. The Company chose the ‘‘straight-line’’ attribution method for allocating compensation costs and recognized the fair value of each stock option on a straight-line basis over the vesting period of the related awards.

The Company uses the Black-Scholes option pricing model when estimating the grant date fair value for stock-based awards. Use of a valuation model requires management to make certain assumptions with respect to selected model inputs. Expected volatility was based on our historical volatility since our initial public offering in May 2007. Beginning in the third quarter of 2017, the average expected life is determined using our actual historical data versus a ‘‘simplified’’ method used in prior quarters. The ‘‘simplified’’ method of estimating the Company did not have sufficient reliable exercise data to justify a change from the use of the ‘‘simplified’’ method of estimating the expected exercise term of employee stock option grants. The impact from this change was not material. The risk-free interest rate is based on U.S. Treasury, zero-coupon issues with a remaining term equal to the expected life assumed at the date of grant. Forfeitures are estimated based on voluntary termination behavior, as well as a historical analysis of actual option forfeitures.

The fair value of the stock options granted is estimated on the date of grant using a Black-Scholes option pricing model with the following weighted-average assumptions:



	Years Ended December 31,
	2019			2018			2017
Expected stock price volatility	74.1		%	78.6		%	82.8		%
Risk free interest rate	2.4		%	2.4		%	2.0		%
Expected life of options (years) ⁽¹⁾	5.68			5.62			6.18
Expected annual dividend per share	$	0.00		$	0.00		$	0.00

______________________________________

⁽¹⁾The average expected life is determined using actual historical data.

The weighted average grant-date fair value per share of options granted during 2019, 2018, and 2017 were $6.67, $10.19, and $5.09, respectively.

A summary of the Company's stock options for the year ended December 31, 2019 were as follows:



	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Years	Aggregate Intrinsic Value
	(in thousands)					(in millions)
Options outstanding, December 31, 2016	15,497.5		$	7.37
Granted	3,695.3		$	7.17
Exercised	(2,878.7	)	$	5.67
Forfeited	(1,133.0	)	$	9.55
Options outstanding, December 31, 2017	15,181.1		$	7.48
Granted	2,348.0		$	14.96
Exercised	(1,398.0	)	$	6.54
Forfeited	(313.1	)	$	9.55
Expired	(8.0	)	$	10.76
Options outstanding, December 31, 2018	15,810.0		$	8.63
Granted	4,091.0		$	10.29
Exercised	(1,967.0	)	$	5.83
Forfeited	(879.0	)	$	11.07
Expired	(331.0	)	$	13.38
Options outstanding, December 31, 2019	16,724.0		$	9.15	6.4	$	30.8
Vested and unvested expected to vest, December 31, 2019	16,111.2		$	9.08	6.3	$	30.6
Exercisable at December 31, 2019	10,646.5		$	8.33	5.1	$	27.0

The aggregate intrinsic value of options exercised during the years ended December 31, 2019, 2018 and 2017 was $11.8 million, $11.9 million, and $20.8 million respectively. Cash proceeds from stock options exercised during the years ended December 31, 2019, 2018, and 2017 were $11.5 million, $9.1 million, and $16.3 million, respectively. As of December 31, 2019, the total unrecognized compensation cost related to non-vested stock options granted was $32.4 million and is expected to be recognized over a weighted average period of 2.5 years.

Restricted Stock Units and Performance-Based Restricted Stock Units (collectively "RSU's")

RSUs awarded under the Plan are generally subject to graded vesting and are contingent on an employee’s continued service. RSUs are generally subject to forfeiture if employment terminates prior to the release of vesting restrictions. The Company expenses the cost of the RSUs, which is determined to be the fair market value of the shares of common stock underlying the RSUs at the date of grant, ratably over the period during which the vesting restrictions lapse. A summary of non-vested RSU activity under the Plan for the year ended December 31, 2019 is as follows:



	Number of Share		Weighted Average Grant Date Fair Value		Weighted Average Remaining Years	Aggregate Intrinsic Value
	(in thousands)					(in millions)
Non-vested units as of December 31, 2017	2,575.1		$	5.85
Granted	1,811.9		$	16.11
Vested	(530.0	)	$	6.01
Forfeited	(145.0	)	$	9.65
Non-vested units as of December 31, 2018	3,712.0		$	10.59
Granted	3,526.0		$	10.92
Vested	(921.0	)	$	8.49
Forfeited	(525.0	)	$	10.52
Non-vested units as of December 31, 2019	5,792.0		$	11.18	2.4	$	56.4

For the year ended December 31, 2019, 920,782 RSUs have vested and all non-vested units are expected to vest over their normal term. As of December 31, 2019, there was $39.8 million of total unrecognized compensation cost related to unvested RSUs with service-based vesting conditions. These costs are expected to be recognized over a weighted average period of 2.4 years.

Compensation Expense Related to Equity Awards

The following table summarizes information related to compensation expense recognized in the Consolidated Statements of Operations related to the equity awards:



	Years Ended December 31,
(in thousands)	2019		2018		2017
Equity compensation expense recognized in:
Research and development expense	$	17,575	$	11,740	$	10,328
Selling, general, and administrative expense	26,855		17,520		12,773
Total equity compensation expense	$	44,430	$	29,260	$	23,101

Assets and Liabilities Measured at Fair Value

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Assets and Liabilities Measured at Fair Value

The Company's financial assets and liabilities are measured at fair value and classified within the fair value hierarchy which is defined as follows:

Level 1 — Quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date.

Level 2 — Inputs other than quoted prices in active markets that are observable for the asset or liability, either directly or indirectly.

Level 3 — Inputs that are unobservable for the asset or liability.

A summary of the fair value of the Company's recurring assets and liabilities aggregated by the level in the fair value hierarchy within which those measurements fall as of December 31, 2019 are identified in the following table:



(in thousands)	Level 2		Total
Assets:
Commercial paper	$	73,710	$	73,710
Asset-back securities	77,810		77,810
Corporate debt securities	145,991		145,991
U.S. Government Agency Bonds	11,991		11,991
Money market funds	4,768		4,768
	$	314,270	$	314,270



(in thousands)	Level 2		Level 3		Total
Liabilities:
Contingent consideration payable	$	—	$	22,681	$	22,681
Deferred compensation plan liability	4,419		—		4,419
	$	4,419	$	22,681	$	27,100



(in thousands)	Level 2		Total
Assets:
Commercial paper	$	115,141	$	115,141
Asset-back securities	68,135		68,135
Corporate debt securities	240,726		240,726
Money market funds	3,082		3,082
	$	427,084	$	427,084



(in thousands)	Level 2		Level 3		Total
Liabilities:
Contingent consideration payable	$	—	$	19,700	$	19,700
Deferred compensation plan liability	2,732		—		2,732
	$	2,732	$	19,700	$	22,432

The Company’s Convertible Notes falls into the Level 2 category within the fair value level hierarchy. The fair value was determined using broker quotes in a non-active market for valuation. The fair value of the Convertible Notes at December 31, 2019 was approximately $5.0 million.

The Company’s Senior Secured Term Loan fall into the Level 2 category within the fair value level hierarchy and the fair value was determined using quoted prices for similar liabilities in active markets, as well as inputs that are observable for the liability (other than quoted prices), such as interest rates that are observable at commonly quoted intervals. The carrying value of the Senior Secured Term Loan approximates the fair value.

The Company did not have any Level 3 assets as of December 31, 2019 or December 31, 2018.

Cash, Money Market Funds and Marketable Securities

The Company classifies its cash within the fair value hierarchy as Level 1 as these assets are valued using quoted prices in an active market for identical assets at the measurement date. The Company considers its investments in marketable securities as available-for-sale and classifies these assets and the money market funds within the fair value hierarchy as Level 2 primarily utilizing broker quotes in a non-active market for valuation of these securities. No changes in valuation techniques or inputs occurred during the year ended December 31, 2019. No transfers of assets between Level 1 and Level 2 of the fair value measurement hierarchy occurred during the year ended December 31, 2019.

Contingent Consideration Payable

The contingent consideration payable resulted from the acquisition of Callidus, as discussed in "— Note 3. Acquisitions." The most recent valuation was determined using a probability weighted discounted cash flow valuation approach. Using this approach, expected future cash flows are calculated over the expected life of the agreement, are discounted, and then exercise scenario probabilities are applied. The valuation is performed quarterly. Gains and losses are included in the Consolidated Statements of Operations.

The contingent consideration payable for Callidus has been classified as a Level 3 recurring liability as its valuation requires substantial judgment and estimation of factors that are not currently observable in the market. If different assumptions were used for the various inputs to the valuation approach, the estimated fair value could be significantly higher or lower than the fair value the Company determined. The Company may be required to record losses in future periods.

The following significant unobservable inputs were used in the valuation of the contingent consideration payable of Callidus for the ATB-200 Pompe program:



Contingent Consideration Liability	Fair value as of December 31, 2019		Valuation Technique	Unobservable Input	Range
	(in thousands)
				Discount rate	9.6%
Clinical and regulatory milestones	$	22,390	Probability weighted discounted cash flow	Probability of achievement of milestones	75% - 78%
				Projected year of payments	2021 - 2022

Contingent consideration liabilities are remeasured to fair value each reporting period using discount rates, probabilities of payment, and projected payment dates. Projected contingent payment amounts related to clinical and regulatory based milestones are discounted back to the current period using a discounted cash flow model. Increases in discount rates and the time to payment may result in lower fair value measurements. Increases or decreases in any of those inputs together, or in isolation, may result in a significantly lower or higher fair value measurement. There is no assurance that any of the conditions for the milestone payments will be met.

The Company reached a clinical milestone, which was the dosing of the first patient in a Phase 3 study, related to the contingent consideration from the acquisition of Callidus. The milestone for this event was $9.0 million, which was paid in Company common stock in the first quarter of 2019, resulting in $9.3 million impact on stockholder's equity.

The following table shows the change in the balance of contingent consideration payable for the year ended December 31, 2019 and 2018, respectively:



	Year ended December 31,
(in thousands)	2019			2018
Balance, beginning of the period	$	19,700		$	25,400
Milestones payable, included in accrued expenses	—			(9,000		)
Changes in fair value during the period, included in the Consolidated Statements of Operations	3,297			3,300
Adjustment for contingent consideration paid in stock	(316		)	—
Balance, end of the period	$	22,681		$	19,700

Deferred Compensation Plan - Investment and Liability

The Deferred Compensation Plan (the "Deferral Plan") provides certain key employees and members of the Board of Directors with an opportunity to defer the receipt of such participant’s base salary, bonus and director’s fees, as applicable. Deferral Plan assets are classified as trading securities and recorded at fair value with changes in the investment’s fair value recognized in the period they occur. The asset investments consist of market exchanged mutual funds. The Company considers its investments in marketable securities as available-for-sale and classifies these assets and related liability within the fair value hierarchy as Level 2, primarily utilizing broker quotes in a non-active market for valuation of these securities.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Debt

12 Months Ended

Dec. 31, 2019

Debt Disclosure [Abstract]

Debt

Senior Secured Term Loan due 2023

In September 2018, the Company entered into a loan agreement with BioPharma Credit PLC as the lender. The loan agreement provides for a $150 million senior secured term loan ("Senior Secured Term Loan") with an interest rate equal to the 3-month LIBOR plus 7.50% per annum and matures in 5 years from the maturity date. The Senior Secured Term Loan will be repaid in four quarterly payments equal to 12.50% thereof starting on the forty-eight month anniversary of the date of the first credit extension with the balance due on the Maturity Date. Interest is payable quarterly in arrears. The Senior Secured Term Loan contains certain customary representations and warranties, affirmative and negative covenants, and events of default applicable to the Company and certain of its subsidiaries but does not include any financial covenants relating to the achievement or maintenance of revenue or cash flow. If an event of default occurs and is continuing, the lender may declare all amounts outstanding under the Senior Secured Term Loan to be immediately due and payable. The Company received net proceeds of $146.6 million in September 2018, after deducting fees and estimated expenses.

Convertible Notes due 2023

In December 2016, the Company issued at par value $250 million aggregate principal amount of Convertible Notes, which included the exercise in full of the $25 million over-allotment option granted to the initial purchasers of the Convertible Notes in a private offering to qualified institutional buyers pursuant to Rule 144A under the Securities Act (the "Note Offering"). Interest is payable semiannually on June 15 and December 15 of each year, beginning on June 15, 2017. The Convertible Notes will mature on December 15, 2023, unless earlier repurchased, redeemed, or converted in accordance with their terms. The Convertible Notes are convertible at the option of the Holders, under certain circumstances and during certain periods, into cash, shares of the Company’s common stock or a combination thereof. The net proceeds from the Note Offering were $243.0 million, after deducting fees and estimated expenses. In addition, the Company used approximately $13.5 million of the net proceeds from the issuance of the Convertible Notes to pay the cost of the capped call transactions ("Capped Call Confirmations") that the Company entered into in connection with the issuance of the Convertible Notes. In accounting for the issuance of the Convertible Notes, the Company separated the Convertible Notes into liability and equity components based on their relative values. The Convertible Notes were initially convertible into approximately 40.8 million shares of the Company’s common stock under certain circumstances prior to maturity at a conversion rate of 163.3987 shares per $1,000 principal amount of Convertible Notes, which represents a conversion price of approximately $6.12 per share of common stock, subject to adjustment under certain conditions. Holders may convert their Convertible Notes at their option at specified times prior to the maturity date of December 15, 2023, only if:

•

during any fiscal quarter commencing after March 31, 2017, if the last reported sale price of the Company’s common stock for at least 20 trading days in the period of 30 consecutive trading days ending on the last trading day of the immediately preceding fiscal quarter is equal to or more than 130% of the conversion price of the Convertible Notes on the last day of such preceding fiscal quarter;

•

a holder submits its Convertible Notes for conversion during the five business day period following any five consecutive trading day period in which the trading price for the Convertible Notes, per $1,000 principal amount of the Convertible Notes, for each such trading day was less than 98% of the product of the last reported sale price of the Company’s common stock and the conversion rate of the Convertible Notes on such date;

•

the Company issues to all or substantially all of the holders of common stock rights options or warrants entitling then them for a period of not more than 60 calendar days after the date of such issuance to subscribe for or purchase shares of the common stock, at a price per share less than the average of the Last Reported Sale Prices of the common stock for the 10 consecutive Trading Day period ending on, and including, the Trading Day immediately preceding the date of announcement of such issuance or distributes to all or substantially all holders of the common stock the Company’s assets, debt securities or rights to purchase the Company’s securities which distribution has a per share value of exceeding 10% of the Last Reported Sale Price of the common stock on the Trading Day immediately preceding the date of announcement of such distribution;


•	the Company enters into specified corporate transactions; or


•	the Company has had a call for redemption, the holder can convert up until the second trading day immediately preceding the redemption date.

The Convertible Notes will be convertible, at the option of the note holders, regardless of whether any of the foregoing conditions have been satisfied, on or after September 15, 2023 at any time prior to the close of business on the second scheduled trading day immediately preceding the stated maturity date of December 15, 2023.

On February 15, 2018, the Company entered into an underwriting agreement relating to an underwritten public offering of 19.4 million shares of the Company’s common stock. Under the terms of the underwriting agreement, the Company granted the underwriters an option, exercisable for 30 days after February 16, 2018, to purchase up to an additional 2.9 million shares of the Company’s common stock, which was exercised with respect to 885,000 shares of the Company’s common stock.

Subsequent to the underwritten public offering on February 15, 2018, the Company did not have sufficient unissued authorized shares to cover a conversion of the Convertible Notes. As a result, the Company accounted for the portion of the bifurcated conversion feature and of the Capped Call Confirmations that would not be able to be net share settled as a current derivative liability and as a derivative asset, respectively. The fair value of the derivative liability for the conversion feature and derivative asset for the Capped Call Confirmations at February 15, 2018 was determined to be $507.4 million and $13.6 million, respectively, of which the portion that was determined to not be able to be net share settled was recorded with a corresponding impact to additional-paid-in-capital. Subsequent changes to fair value of the derivatives were recorded in the second quarter of 2018 through earnings on the Company’s Consolidated Statements of Operations resulting in a change in fair value of derivatives for the year ended December 31, 2018 of $2.7 million.

Following the approval by the stockholders of the Company on June 7, 2018, to increase the authorized shares of common stock to 500,000,000, the Company has sufficient unissued authorized shares to cover a conversion of the Convertible Notes. As a result, the derivative liability and derivative asset were reclassified into additional-paid-in-capital. The fair value of the derivative liability for the conversion feature and derivative asset for the Capped Call Confirmations at June 7, 2018 was determined to be $88.3 million and $2.4 million, respectively.

The Capped Call Confirmations were expected generally to reduce the potential dilution to the common stock upon any conversion of the Convertible Notes and/or offset the cash payments the Company is required to make in excess of the principal amount upon conversion of the Convertible Notes in the event that the market price of the common stock was greater than the strike price of the Capped Call Confirmations (which initially corresponded to the initial conversion price of the Convertible Notes and is subject to certain adjustments under the terms of the Capped Call Confirmations), with such reduction and/or offset subject to a cap based on the cap price of the Capped Call Confirmations. The Capped Call Confirmations had an initial cap price of $7.20 per share, which represented a premium of approximately 50% over the closing price of the Company’s common stock on The NASDAQ Global Market on December 15, 2016 and was subject to certain adjustments under the terms of the Capped Call Confirmations. The Capped Call Confirmations covered, subject to anti-dilution adjustments substantially similar to those applicable to the Convertible Notes, the number of shares of common stock that underlay the Convertible Notes. The Capped Call Confirmations did not meet the criteria for separate accounting as a derivative as they were indexed to the Company’s common stock. The premiums paid for the Capped Call Confirmations were included as a net reduction to additional paid-in capital.

During the first and second quarters of 2019, the Company entered into separate, privately negotiated Exchange Agreements with the Holders of the Convertible Notes. Under the terms of the Exchange Agreements, the Holders agreed to exchange an aggregate principal amount of $247.2 million of Convertible Notes held by them in exchange for an aggregate of approximately 44.0 million shares of Company common stock, par value $0.01 per share. In addition, pursuant to the Exchange Agreements, the Company made aggregate cash payments of $1.3 million to the Holders to satisfy accrued and unpaid interest to the closing date of the transactions, along with cash in lieu of fractional shares. These transactions resulted in $215.0 million in additional paid-in-capital and common stock of $0.4 million on the Consolidated Balance Sheets as of December 31, 2019. Additionally, the Company recognized a net loss on the exchange of debt of $40.6 million on the Consolidated Statements of Operations during the year ended December 31, 2019. During the second half of the year there were no additional debt conversion transactions.

During the first and second quarter of 2019, the Company terminated the Capped Call Confirmations related to the exchange of the Convertible Notes for proceeds of approximately $19.9 million.

The last reported sale price of the Company’s common stock was equal to or more than 130% of the conversion price of the Convertible Notes for at least 20 trading days of the 30 consecutive trading days ending on the last day of the year. As a result, the Convertible Notes are currently convertible into the Company’s common stock.

The Convertible Notes and Senior Secured Term Loan consist of the following:



	As of December 31,
(in thousands)	2019			2018
Principal	$	152,825		$	400,000
Less: debt discount ⁽¹⁾	(2,974		)	(74,145		)
Less: deferred financing ⁽¹⁾	(346		)	(4,115		)
Net carrying value of the debt	$	149,505		$	321,740

______________________________


⁽¹⁾	Included in the Consolidated Balance Sheets within Convertible Notes and Senior Secured Term Loan and amortized to interest expense over the remaining life of the Convertible Notes and Senior Secured Term Loan using the effective interest rate method.

The following table sets forth interest expense recognized related to the Convertible Notes and Senior Secured Term Loan for the years ended December 31, 2019 and 2018 respectively:



(in thousands)	2019			2018
Contractual interest expense	$	16,483		$	11,426
Amortization of debt discount	$	2,381		$	10,421
Amortization of deferred financing	$	165		$	555
Effective interest rate of the liability component, Convertible debt	10.63		%	10.85		%
Effective interest rate of the liability component, Senior Secured Term Loan	10.16		%	10.48		%

Leases

12 Months Ended

Dec. 31, 2019

Leases [Abstract]

Leases

The Company currently has operating leases for office and research laboratory space, equipment, and vehicles under agreements expiring at various dates through 2044, which include renewal options on leases which the Company is reasonably certain to exercise.

For the year ended December 31, 2019, operating lease expense was $10.8 million. For the year ended December 31, 2019, the Company paid $4.9 million for amounts included in the measurement of operating lease liabilities and recorded $21.8 million of right-of-use assets and $19.4 million of tenant improvements paid through lease incentives in exchange for new operating lease liabilities.

Commitments under finance leases are not significant.

Supplemental balance sheet information related to operating leases was as follows:



(in thousands, except year and discount rate amounts)	December 31, 2019
Operating lease ROU asset	$	33,315

Current portion of the operating lease liabilities	$	7,189
Non-current portion of the operating lease liabilities	53,531
Total operating lease liability	$	60,720

Weighted-average remaining lease terms (years)	18.2
Weighted-average discount rate	13.1		%

At December 31, 2019, the future minimum operating lease payments were as follows:



(in thousands)	Operating Lease
2020	$	9,738
2021	10,787
2022	10,459
2023	10,809
2024	10,582
Thereafter	163,266
Total lease payments	215,641
Less lease incentives	(28,939		)
Less imputed interest	(125,982		)
Total operating lease liability	$	60,720

At December 31, 2018, the future minimum operating lease payments were as follows:



(in thousands)	Operating Lease
2019	$	6,244
2020	4,063
2021	3,560
2022	3,371
2023	3,611
Thereafter	10,038
Total lease payments	$	30,887

Rent expense, including fees for utilities and common area maintenances under ASC 840 for the years ended December 31, 2018 and 2017 were $5.7 million and $3.9 million, respectively.

Income Taxes

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Income Taxes

For financial reporting purposes, income (loss) before income taxes includes the following components:



	Years Ended December 31,
(in thousands)	2019			2018			2017
United States	$	(393,955	)	$	(309,183	)	$	(440,696	)
Foreign	38,045			(39,906		)	(8,425		)
Total	$	(355,910	)	$	(349,089	)	$	(449,121	)

Following were the components of income tax expense (benefit) for the years ended December 31, 2019, 2018, and 2017:



(in thousands)	2019			2018			2017
Current
Federal	$	—		$	—		$	—
State	—			6			9
Foreign	2,877			(100		)	2,276
Deferred
Federal	(984		)	—			(150,015		)
State	(1,415		)	—			(17,389		)
Foreign	—			—			—
Total	$	478		$	(94	)	$	(165,119	)

A reconciliation of the statutory tax rates and the effective tax rates for the years ended December 31, 2019, 2018 and 2017 are as follows:



	Years Ended December 31,
	2019		2018		2017
Statutory rate	(21	)%	(21	)%	(34	)%
State taxes, net of federal benefit	—		(4	)	(5	)
Nondeductible IPR&D	—		6		(1	)
Contingent consideration	—		1		(18	)
Tax credits	(16	)	(10	)	(2	)
Foreign income tax rate differential	9		2		5
Impact of 2017 Act	—		—		27
Nondeductible debt conversion	(1	)	—		—
Other	—		—		5
Valuation allowance	29		26		(14	)
Net	—	%	—	%	(37	)%

On December 22, 2017, the U.S. government enacted the Tax Cuts and Jobs Act ("Tax Act"). The Tax Act significantly revises U.S. tax law by, among other provisions, lowering the U.S. federal statutory income tax rate to 21%, imposing a mandatory one-time transition tax on previously deferred foreign earnings, and eliminating or reducing certain income tax deductions.

ASC 740, Income Taxes, requires the effects of changes in tax laws to be recognized in the period in which the legislation is enacted. However, due to the complexity and significance of the Tax Act's provisions, the SEC staff issued SAB 118, which allows companies to record the tax effects of the Tax Act on a provisional basis based on a reasonable estimate, and then, if necessary, subsequently adjust such amounts during a limited measurement period as more information becomes available. The measurement period ends when a company has obtained, prepared, and analyzed the information necessary to finalize its accounting, but cannot extend beyond one year from enactment. The Tax Act did not have a material impact on the Company's financial statements because its deferred temporary differences are fully offset by a valuation allowance. The Company did not have any significant offshore earnings from which to record the mandatory transition tax. During 2018 the Company operated in a consolidated loss position in its foreign operations and did not have a one-time tax on accumulated earnings of foreign subsidiaries.

As of December 31, 2017, the Company provisionally recorded certain impacts of the Tax Act including the adjustment to our net deferred tax liability arising from the reduction in the federal tax rate as well as the impact of mandatory deemed repatriation. Adjustments to these provisional amounts that we recorded in 2018 did not have a significant impact on the Company's Consolidated Financial Statements. The Company's accounting for the effects of the enactment of the Tax Act are now complete.

The Company recorded an income tax expense of $2.9 million in 2019 for taxes in foreign jurisdictions and a $2.4 million tax benefit in 2019 for taxes in U.S. federal and state jurisdictions.

The Company did not recognize interest or penalties related to income tax during the period ended December 31, 2019 and did not accrue for interest or penalties as of December 31, 2019. The Company does not have an accrual for uncertain tax positions as of December 31, 2019. Tax returns for years 2015 through 2018 are open to examination by tax authorities. The Company is also subject to examination in any period for which it has net operating losses.

Deferred income taxes reflect the net effect of temporary difference between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. The significant components of the deferred tax assets and liabilities are as follows:



	For Years Ended December 31,
(in thousands)	2019			2018
Deferred tax assets
Intellectual property	$	46,521		$	48,339
Amortization/depreciation	2,329			3,732
Research tax credit	141,669			96,509
Net operating loss carry forwards	286,850			248,398
Deferred reimbursement	2,230			4,401
Non-cash stock issue	19,058			16,850
Interest carry forward limitation	2,224			1,032
Other	15,986			10,852
Gross deferred tax assets	516,867			430,113
Deferred tax liabilities
Business acquisition	(5,051		)	(6,465		)
Royalty payable	(46,521		)	(48,339		)
Convertible notes	(653		)	(16,666		)
Advanced R&D payments	(2,611		)	(2,103		)
Other	(725		)	—
Total net deferred tax assets	461,306			356,540
Less: valuation allowance	(466,357		)	(363,005		)
Net deferred tax liability	$	(5,051	)	$	(6,465	)

The Company records a valuation allowance for temporary differences for which it is more likely than not that the Company will not receive future tax benefits. At December 31, 2019 and 2018, the Company recorded valuation allowances of $466.4 million and $363.0 million, respectively, representing an increase in the valuation allowance of $103.4 million in 2019, due to the uncertainty regarding the realization of such deferred tax assets, to offset the benefits of net operating losses generated during those years. The deferred tax liability related to business acquisitions pertains to the basis difference in IPR&D acquired by the Company. The Company's policy is to record a deferred tax liability related to acquired IPR&D that may eventually be realized either upon amortization of the asset when the research is completed, and a product is successfully launched or the write-off of the asset if it is abandoned or unsuccessful.

As of December 31, 2019, the Company had federal, state, and foreign net operating loss carry forwards ("NOLs") of approximately $1,036 million, $897.8 million, and $30.6 million, respectively. The federal carry forward for losses generated prior to 2018 will expire in 2029 through 2037. Federal net operating losses incurred in 2018 and onward have an indefinite expiration under the 2017 Tax Act. Most of the state carry forwards generated prior to 2009 have expired through 2016. The remaining state carry forwards including those generated in 2009 through 2019 will expire in 2029 through 2039. The foreign NOLs are subject to differing expirations beginning in 2026. Utilization of NOLs may be subject to a substantial limitation pursuant to Section 382 of the Internal Revenue Code of 1986, as amended ( the "Code") as well as similar state statutes in the event of an ownership change. Such ownership changes have occurred in the past and could occur again in the future. Under Section 382 of the Internal Revenue Code of 1986, as amended, or Section 382, if a corporation undergoes an "ownership change," generally defined as a greater than 50% change (by value) in its equity ownership over a three-year period, the corporation's ability to use its pre-change NOLs and other pre-change tax attributes (such as research and development tax credits) to offset its post-change income may be limited. We may experience ownership changes in the future as a result of shifts in our stock ownership some of which are outside our control. We completed a detailed study of our NOLs and determined that there was not an ownership change in excess of 50%. Ownership changes in future periods may place additional limits on our ability to utilize net operating loss and tax credit carry forwards. In addition, at the state level, there may be periods during which the use of NOLs is suspended or otherwise limited, which could accelerate or permanently increase state taxes owed.

The Company also has research and experimentation and orphan drug credit carryforwards of approximately $27.6 million and $114.0 million, respectively, which will expire in the years 2021 through 2039. Deferred tax assets for these carryforwards are subject to a full valuation allowance.

Collaborative Agreements

12 Months Ended

Dec. 31, 2019

Collaborative Agreements

Collaborative Agreements

Penn

In October 2018, the Company expanded its gene therapy portfolio through a collaboration agreement with Penn to pursue research and development of novel gene therapies for four additional indications, including Pompe disease, Fabry disease, CDD and one additional undisclosed rare metabolic disorder.

In May 2019, the Company further expanded the collaboration from three to six programs for rare genetic diseases and now includes specifically: NPC, MPS IIIB, as well as a next generation program in MPS IIIA. This expanded collaboration with Penn also provides the Company with exclusive disease-specific access and option rights to develop potentially disruptive new gene therapy platform technologies and programs for most LDs and a broader portfolio of rare diseases, including Rett Syndrome, Angelman Syndrome, Myotonic Dystrophy, and select other muscular dystrophies. Under the expanded collaboration agreement with Penn, Penn is eligible to receive certain milestone, royalty and discovery research payments with respect to licensed products for each indication. Milestone payments are payable following the achievement of certain development and commercial milestone events in each indication, up to an aggregate of $86.5 million per indication. Royalty payments are based on net sales of licensed products on a licensed product-by-licensed product and country- by-country basis. The Company will provide $10.0 million each year during the five-year agreement to fund the discovery research program. In connection with the collaboration agreement, the Company made an upfront payment of $7 million in cash to Penn that was expensed to research and development expense in the Consolidated Statements of Operations.

GlaxoSmithKline

In November 2013, Amicus entered into the Revised Agreement with GlaxoSmithKline ("GSK"), pursuant to which Amicus has obtained global rights to develop and commercialize Galafold^® as a monotherapy and in combination with ERT for Fabry disease. The Revised Agreement amends and replaces in its entirety the earlier agreement entered into between Amicus and GSK in July 2012 ("Expanded Collaboration Agreement"). Under the terms of the Revised Agreement, there was no upfront payment from Amicus to GSK. For Galafold^® monotherapy, GSK is eligible to receive post-approval and sales-based milestones up to $40 million, as well as tiered royalties in the mid-teens in eight major markets outside the U.S. For the year ended December 31, 2019, the Company incurred approximately $15.5 million of royalty expenses under the revised agreement with GSK.

Under the terms of the Revised Agreement, GSK will no longer jointly fund development costs for all formulations of Galafold^®.

In evaluating the impact of both the Expanded Collaboration Agreement and the Revised Agreement, the Company applied the accounting guidance regarding the impact of potential future payments it may make in its role as a vendor (i.e., Amicus) to its customer (i.e., GSK) and evaluated if these potential future payments could be a reduction of revenue from GSK. If the potential future payments to GSK are as follows:


•	a payment for an identifiable benefit, and


•	the identifiable benefit is separable from the existing relationship between the Company and GSK, and


•	the identifiable benefit can be obtained from a party other than GSK, and


•	the Company can reasonably estimate the fair value of the identifiable benefit,

then the potential future payments would be treated separately from the collaboration and research revenue. However, if all these criteria are not satisfied, then the potential future payments are treated as a reduction of revenue.

Accordingly, the Company did not believe that, for accounting purposes, the new U.S. licensing rights to Galafold^® obtained from GSK under the Expanded Collaboration Agreement, nor the ex U.S. licensing rights to Galafold^® obtained from GSK under the Revised Agreement, represented a separate, identifiable benefit from the licenses in the Original Collaboration Agreement entered into between Amicus and GSK in 2010. The contingent amounts payable to GSK were not sufficiently separable from GSK's original license and the research and development reimbursements such that Amicus could not have entered into a similar exchange transaction with another party. Additionally, the Company cannot reasonably estimate the fair value of the worldwide licensing rights to Galafold^®.

The Company determined that the potential future payments to GSK would be treated as a reduction of revenue and that the total amount of revenue to be received under the arrangement is no longer fixed or determinable as the contingent milestone payments are subject to significant uncertainty.

As a result, the Company no longer recognized any of the upfront license fees and premiums on the equity purchase from GSK until such time as the arrangement consideration becomes fixed or determinable, because an indeterminable amount may ultimately be payable back to GSK. These amounts (the balance of the unrecognized upfront license fee and the premium on the equity purchases) are classified as deferred reimbursements on the balance sheet.

For the year ended December 31, 2019, under the GSK collaboration agreements, we paid $1.5 million in sales-based milestones. As of December 31, 2019, the Company recognized another $4.0 million for sales-based milestones that were met, invoiced and recorded in accounts payable, accrued expenses and other current liabilities and $10.2 million was recorded as deferred reimbursements in the Consolidated Balance Sheets. Additionally, the Company recognized a liability of $5.2 million related to royalties payable to GSK in accounts payable and accrued expenses in the Consolidated Balance Sheets.

The recognition of Research Revenue was also affected by the determination that the overall total arrangement consideration was no longer fixed and determinable, despite the fact that the research activities continued and that the research expense reimbursements by GSK to Amicus were received as the research activities related to the reimbursement had been completed. Therefore, the research reimbursements from GSK were recorded as deferred reimbursements on the balance sheet and would not be recognized until the total arrangement consideration becomes fixed and determinable.

As a result, all revenue recognition was suspended until the total arrangement consideration would become fixed and determinable. In addition, future milestone payments made by the Company will be applied against the balance of this deferred reimbursements account. Revenue recognition for research expense reimbursements, the original upfront license fee, and the equity premiums will resume once the total arrangement consideration becomes fixed and determinable which will occur when the balance of the deferred reimbursements account is sufficient to cover all the remaining contingent milestone payments.

Basic and Diluted Net Loss per Common Share

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

Basic and Diluted Net Loss per Common Share

The following table provides a reconciliation of the numerator and denominator used in computing basic and diluted net loss attributable to common stockholders per common share:



	Years Ended December 31,
(in thousands, except per share amounts)	2019			2018			2017
Numerator:
Net loss attributable to common stockholders	$	(356,388	)	$	(348,995	)	$	(284,002	)
Denominator:
Weighted average common shares outstanding — basic and diluted	240,421,001			185,790,021			153,355,144

Dilutive common stock equivalents would include the dilutive effect of common stock options, convertible debt units, RSUs and warrants for common stock equivalents. Potentially dilutive common stock equivalents were excluded from the diluted earnings per share denominator for all periods because of their anti-dilutive effect. For the year ended December 31, 2019 there were 462 thousand potential common shares outstanding as a result of the Convertible Debt that were excluded from the diluted net loss per share calculation because their effect would have been anti-dilutive.

The table below presents potential shares of common stock that were excluded from the computation as they were anti-dilutive using the treasury stock method:



	Year ended December 31,
(in thousands)	2019	2018	2017
Options to purchase common stock	16,724	15,810	15,181
Convertible debt	462	40,850	40,850
Outstanding warrants, convertible to common stock	2,555	2,657	3,110
Unvested restricted stock units	5,792	3,712	2,575
Vested restricted stock units, unissued	186	91	50
Total number of potentially issuable shares	25,719	63,120	61,766

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Data (Unaudited)



	Quarters Ended
(in thousands except per share data)	March 31			June 30			September 30			December 31
2019
Net product sales	$	34,046		$	44,130		$	48,768		$	55,293
Net loss	$	(120,299	)	$	(84,551	)	$	(61,809	)	$	(89,729	)
Basic and diluted net loss per common share ⁽¹⁾	$	(0.56	)	$	(0.36	)	$	(0.24	)	$	(0.35	)
2018
Net product sales	$	16,696		$	21,309		$	20,596		$	32,644
Net loss	$	(49,916	)	$	(61,833	)	$	(159,163	)	$	(78,083	)
Basic and diluted net loss per common share ⁽¹⁾	$	(0.28	)	$	(0.33	)	$	(0.84	)	$	(0.43	)

______________________________

⁽¹⁾Per common share amounts for the quarters and full years have been calculated separately. Accordingly, quarterly amounts do not add to the annual amounts because of differences on the weighted-average common shares outstanding during each period principally due to the effect of the Company issuing shares of its common stock during the year.

Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The Company has prepared the accompanying Consolidated Financial Statements in accordance with U.S. generally accepted accounting principles ("U.S. GAAP") and include all adjustments necessary for the fair presentation of the Company's financial position for the periods presented.
Consolidation	Consolidation The Consolidated Financial Statements include the accounts of the Company and its subsidiaries. Intercompany accounts and transactions are eliminated in consolidation.
Foreign Currency Transactions	Foreign Currency Transactions The functional currency for most of the Company's foreign subsidiaries is their local currency. For non-U.S. subsidiaries that transact in a functional currency other than the U.S. dollar, assets and liabilities are translated at current rates of exchange at the balance sheet date. Income and expense items are translated at the average foreign exchange rates for the period. Adjustments resulting from the translation of the financial statements of the Company's foreign operations into U.S. dollars are excluded from the determination of net income and are recorded in accumulated other comprehensive income, a separate component of stockholders' equity.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting periods. Actual results could differ from those estimates
Cash, Cash Equivalents, Marketable Securities, and Restricted Cash	Cash, Cash Equivalents, Marketable Securities, and Restricted Cash The Company considers all highly liquid investments purchased with a maturity of three months or less at the date of acquisition, to be cash equivalents. Marketable securities consist of fixed income investments with a maturity of greater than three months and other highly liquid investments that can be readily purchased or sold using established markets. These investments are classified as available-for-sale and are reported at fair value on the Company’s Consolidated Balance Sheets. Unrealized holding gains and losses are reported within comprehensive income (loss) in the Statements of Comprehensive Loss. Fair value is based on available market information including quoted market prices, broker or dealer quotations or other observable inputs. Restricted cash consists primarily of funds held to satisfy the requirements of certain agreements that are restricted in their use and is included in non-current assets on the Company’s Consolidated Balance Sheets.
Concentration of Credit Risk	Concentration of Credit Risk The Company's financial instruments that are exposed to concentration of credit risk consist primarily of cash, cash equivalents, and marketable securities. The Company maintains its cash and cash equivalents in bank accounts, which, at times, exceed federally insured limits. The Company invests its marketable securities in high-quality commercial financial instruments. The Company has not recognized any losses from credit risks on such accounts during any of the periods presented. The Company believes it is not exposed to significant credit risk on its cash, cash equivalents, or marketable securities. The Company is subject to credit risk from its accounts receivable related to its product sales of Galafold^®. The Company's accounts receivable at December 31, 2019 have arisen from product sales primarily in Europe and the U.S. The Company will periodically assess the financial strength of its customers to establish allowances for anticipated losses, if any. For accounts receivable that have arisen from named patient sales, the payment terms are predetermined, and the Company evaluates the creditworthiness of each customer on a regular basis.
Property and Equipment	Property and Equipment Property and equipment are stated at cost, less accumulated depreciation. Depreciation is calculated over the estimated useful lives of the respective assets, which range from three to five years, or the lesser of the related initial term of the lease or useful life for leasehold improvements. The initial cost of property and equipment consists of its purchase price and any directly attributable costs of bringing the asset to its working condition and location for its intended use. Expenditures incurred after the fixed assets have been put into operation, such as repairs and maintenance, are charged to income in the period in which the costs are incurred. Major replacements, improvements, and additions are capitalized in accordance with Company policy.
Revenue Recognition	Revenue Recognition The Company’s net product sales consist of sales of Galafold^® for the treatment of Fabry disease. The Company has recorded revenue on sales where Galafold^® is available either on a commercial basis or through a reimbursed early access program ("EAP"). Orders for Galafold^® are generally received from distributors and pharmacies, with the ultimate payor often a government authority. In 2019, one customer accounted for 22% of net product sales and 11% of accounts receivable from product sales. The Company recognizes revenue when its performance obligations to its customers have been satisfied, which occurs at a point in time when the pharmacies or distributors obtain control of Galafold^®. The transaction price is determined based on fixed consideration in the Company’s customer contracts and is recorded net of estimates for variable consideration, which are third-party discounts and rebates. The identified variable consideration is recorded as a reduction of revenue at the time revenues from sales of Galafold^® are recognized. The Company recognizes revenue to the extent that it is probable that a significant revenue reversal will not occur in a future period. These estimates may differ from actual consideration received. The Company evaluates these estimates each reporting period to reflect known changes.
Inventories and Cost of Goods Sold	Inventories and Cost of Goods Sold Inventories are stated at the lower of cost and net realizable value, determined by the first-in, first-out method. Inventories are reviewed periodically to identify slow-moving or obsolete inventory based on projected sales activity as well as product shelf-life. In evaluating the recoverability of inventories produced, the probability that revenue will be obtained from the future sale of the related inventory is considered and inventory value is written down for inventory quantities in excess of expected requirements. Expired inventory is disposed of and the related costs are recognized as cost of product sales in the Consolidated Statements of Operations. Cost of goods sold includes the cost of inventory sold, manufacturing and supply chain costs, product shipping and handling costs, provisions for excess and obsolete inventory, as well as royalties payable.
Fair Value Measurements	Fair Value Measurements The Company records certain asset and liability balances under the fair value measurements as defined by the FASB guidance. Current FASB fair value guidance emphasizes that fair value is a market-based measurement, not an entity-specific measurement. Therefore, a fair value measurement should be determined based on the assumptions that market participants would use in pricing the asset or liability. As a basis for considering market participant assumptions in fair value measurements, current FASB guidance establishes a fair value hierarchy that distinguishes between market participant assumptions based on market data obtained from sources independent of the reporting entity (observable inputs that are classified within Levels 1 and 2 of the hierarchy) and the reporting entity's own assumptions that market participants assumptions would use in pricing assets or liabilities (unobservable inputs classified within Level 3 of the hierarchy). Level 1 inputs utilize quoted prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access at measurement date. Level 2 inputs are inputs other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly. Level 2 inputs may include quoted prices for similar assets and liabilities in active markets, as well as inputs that are observable for the asset or liability (other than quoted prices), such as interest rates, foreign exchange rates, and yield curves that are observable at commonly quoted intervals. Level 3 inputs are unobservable inputs for the asset or liability, which is typically based on an entity's own assumptions, as there is little, if any, related market activity. In instances where the determination of the fair value measurement is based on inputs from different levels of the fair value hierarchy, the level in the fair value hierarchy within which the entire fair value measurement falls is based on the lowest level input that is significant to the fair value measurement in its entirety. The Company's assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment and considers factors specific to the asset or liability.
Contingent Liabilities	Contingent Liabilities On an ongoing basis, the Company may be involved in various claims and legal proceedings. On a quarterly basis, the Company reviews the status of each significant matter and assesses its potential financial exposure. If the potential loss from any claim, asserted or unasserted, or legal proceeding is considered probable and the amount can be reasonably estimated, the Company will accrue a liability for the estimated loss. Because of uncertainties related to claims and litigation, accruals will be based on the Company's best estimates based on available information. On a periodic basis, as additional information becomes available, or based on specific events such as the outcome of litigation or settlement of claims, the Company may reassess the potential liability related to these matters and may revise these estimates, which could result in material adverse adjustments to the Company's operating results.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred. Research and development expense consist primarily of costs related to personnel, including salaries and other personnel related expenses, consulting fees, and the cost of facilities and support services used in drug development. Assets acquired that are used for research and development and have no future alternative use are expensed as in-process research and development.
Interest Income and Interest Expense	Interest Income and Interest Expense Interest income consists of interest earned on the Company's cash, cash equivalents, and marketable securities. Interest expense consists of interest incurred on debt and finance leases.
Income Taxes	Income Taxes The Company accounts for income taxes under the liability method. Under this method deferred income tax liabilities and assets are determined based on the difference between the financial statement carrying amounts and tax basis of assets and liabilities and for operating losses and tax credit carry forwards, using enacted tax rates in effect in the years in which the differences are expected to reverse. A valuation allowance is recorded if it is "more likely than not" that a portion or all of a deferred tax asset will not be realized.
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) Components of other comprehensive income (loss) include unrealized gains and losses on available-for-sale securities and gain (loss) on foreign currency transactions and are included in the Statements of Comprehensive Loss.
Leases	Leases The Company primarily enters into lease agreements for office space, equipment, and vehicles. The leases have varying terms, some of which could include options to renew, extend, and early terminate. The Company determines if an arrangement is a lease at contract inception. Operating leases are included in right-of-use ("ROU") assets and lease liabilities on the Consolidated Balance Sheets. ROU assets represent the Company's right to control the use of an explicitly or implicitly identified fixed asset for a period of time and lease liabilities represent the Company's obligation to make lease payments arising from the lease. Control of an underlying asset is conveyed to the Company if the Company obtains the rights to direct the use of and to obtain substantially all of the economic benefits from using the underlying asset. ROU assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. The Company uses its incremental borrowing rate based on the information available at commencement date in determining the present value of lease payments. Lease payments included in the measurement of the lease liability are comprised of fixed payments. Variable lease payments are excluded from the ROU asset and lease liability and are recognized in the period in which the obligation for those payments is incurred. Variable lease payments are presented in the Consolidated Statements of Operations in the same line item as expenses arising from fixed lease payments for operating leases. The Company has lease agreements that include lease and non-lease components, which the Company accounts for as a single lease component for all underlying asset categories. The lease term for all of the Company's leases include the non-cancellable period of the lease plus any additional periods covered by either a Company option to extend (or not to terminate) the lease that the Company is reasonably certain to exercise, or an option to extend (or not to terminate) the lease controlled by the lessor. Leases with an initial term of 12 months or less are not recorded on the Consolidated Balance Sheets. The Company recognizes lease expense for these leases on a straight-line basis over the lease term. The Company applies this policy to all underlying asset categories. The information presented for the periods prior to January 1, 2019 has not been restated and is reported under the accounting standard in effect for those periods. For additional information, see " -Note 13. Leases" and "-Note 2. Summary of Significant Accounting Policies, Recent Accounting Developments - Guidance Adopted in 2019."
Nonqualified Cash Deferral Plan	Nonqualified Cash Deferral Plan The Company's Cash Deferral Plan (the "Deferral Plan"), provides certain key employees and members of the Board of Directors as selected by the Compensation Committee of the Board of Directors of the Company (the "Compensation Committee"), with an opportunity to defer the receipt of such participant's base salary, bonus, and director's fees, as applicable. The Deferral Plan is intended to be a nonqualified deferred compensation plan that complies with the provisions of Section 409A of the Internal Revenue Code (the "Code"). All of the investments held in the Deferral Plan are classified as investments held-to-maturity and recorded at fair value with changes in the investments' fair value recognized as earnings in the period they occur. The corresponding liability for the Deferral Plan is included in other non-current liability in the Consolidated Balance Sheets.
Equity-based Compensation	Equity-based Compensation At December 31, 2019, the Company had three equity-based employee compensation plans, which are described more fully in "— Note 9. Stockholders' Equity." The Company applies the fair value method of measuring equity-based compensation, which requires a public entity to measure the cost of employee services received in exchange for an award of equity instruments based on the grant-date fair value of the award.
Loss per Common Share	Loss per Common Share The Company calculates net loss per share as a measurement of the Company's performance while giving effect to all dilutive potential common shares that were outstanding during the reporting period. The Company had a net loss for all periods presented; accordingly, the inclusion of common stock options, unvested RSUs, and warrants would be anti-dilutive. Therefore, the weighted average shares used to calculate both basic and diluted earnings per share are the same. See "— Note 17. Basic and Diluted Net Loss per Common Share" for further discussion on net loss per share.
Segment Information	Segment Information The Company currently operates in one business segment focused on the discovery, development, and commercialization of advanced therapies to treat a range of devastating rare and orphan diseases. The Company is not organized by market and is managed and operated as one business. A single management team reports to the chief operating decision maker who comprehensively manages the entire business. The Company does not operate any separate lines of business or separate business entities with respect to its products. Accordingly, the Company does not accumulate discrete financial information with respect to separate service lines, and thus there is one reporting unit.
Business Combinations	Business Combinations The Company assigns fair value to the tangible and intangible assets acquired and liabilities assumed based upon their estimated fair values on the acquisition date from acquired businesses. The purchase price allocation process requires management to make significant estimates and assumptions, especially at the acquisition date with respect to intangible assets and in-process research and development ("IPR&D"). In connection with the purchase price allocations for acquisitions, the Company estimates the fair value of contingent payments utilizing a probability-based income approach inclusive of an estimated discount rate.
Contingent Consideration Payable	Contingent Consideration Payable Contingent consideration payments in asset acquisitions are recognized when the contingency is resolved and the consideration is paid or becomes payable. This does not apply in circumstances when the contingent consideration meets the definition of a derivative, in which case the amount becomes part of the basis in the asset acquired. Upon recognition of the contingent consideration payment, the amount is included in the cost of the acquired asset or group of assets. The Company determines the fair value of contingent acquisition consideration payable on the acquisition date using a probability-based income approach utilizing an appropriate discount rate. Contingent acquisition consideration payable is shown as a non-current liability on the Company's Consolidated Balance Sheets. The fair value of the contingent consideration payable will be determined each period end and the resulting change will be recorded on the Consolidated Statements of Operations.
Intangible Assets and Goodwill	Intangible Assets and Goodwill The Company records goodwill in a business combination when the total consideration exceeds the fair value of the net tangible and identifiable intangible assets acquired. Purchased IPR&D is accounted for as an indefinite lived intangible asset until the underlying project is completed, at which point the intangible asset will be accounted for as a definite lived intangible asset, or abandoned, at which point the intangible asset will be written off or partially impaired. Goodwill and indefinite lived intangible assets are assessed annually for impairment and whenever events or circumstances indicate that the carrying amount of an asset may not be recoverable. If it is determined that the full carrying amount of an asset is not recoverable, an impairment loss is recorded in the amount by which the carrying amount of the asset exceeds its fair value.
Recent Accounting Developments	Recent Accounting Developments - Guidance Adopted in 2019 ASU 2016-02 - In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) ("ASU 2016-02"). ASU 2016-02 requires the recognition of lease assets and lease liabilities on the balance sheet for all lease obligations and disclosing key information about leasing arrangements. ASU 2016-02 requires the recognition of lease assets and lease liabilities by lessees for those leases classified as operating leases under previous generally accepted accounting principles. In August 2018, the FASB issued ASU 2018-11, Leases (Topic 842): Targeted Improvements, ("ASU 2018-11"). ASU 2018-11 provided entities with an additional transition method for adoption, whereby, an entity initially applies the new leases standard at the adoption date and recognizes a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. Effective January 1, 2019 the Company adopted ASU 2016-02, along with the amendments issued in 2017 and 2018, and elected the transition method in ASU 2018-11. The Company elected the package of transition provisions available for expired or existing contracts, which allowed the Company to carry forward its historical assessments of (i) whether contracts are or contain leases, (ii) lease classification and (iii) initial direct costs. In addition, the Company applied the short-term lease recognition exemption for leases with terms at inception not greater than 12 months and will apply the practical expedient not to separate lease and non-lease components for new and modified leases commencing after adoption. The information presented for the periods prior to January 1, 2019 has not been restated and is reported under the accounting standard in effect for those periods. Upon adoption, the Company recorded a lease liability with a corresponding right-of-use asset of $17.6 million. The adoption did not have a material impact on the Consolidated Statements of Operations and the Consolidated Statements of Cash Flows. Recent Accounting Developments - Guidance Not Yet Adopted ASU 2019-12 - In December 2019, the FASB issued ASU 2019-15, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes ("ASU 2019-12"). This new guidance removes specific exceptions to the general principles in Topic 740. It eliminates the need for an organization to analyze whether the following apply in a given period: (i) exception to the incremental approach for intraperiod tax allocation; (ii) exceptions to accounting for basis differences when there are ownership changes in foreign investments; and (iii) exception in interim period income tax accounting for year-to-date losses that exceed anticipated losses. ASU 2019-12 also improves financial statement preparers’ application of income tax-related guidance and simplifies the following: (i) franchise taxes that are partially based on income; (ii) transactions with a government that result in a step up in the tax basis of goodwill; (iii) separate financial statements of legal entities that are not subject to tax; and (iv) enacted changes in tax laws in interim periods. ASU 2019 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. Early adoption is permitted for public business entities for periods for which financial statements have not yet been issued. An entity that elects early adoption in an interim period should reflect any adjustments as of the beginning of the annual period that includes that interim period. Additionally, an entity that elects early adoption should adopt all the amendments in the same period. The Company is currently assessing the impact that this standard will have on its Consolidated Financial Statements upon adoption. ASU 2018-15 - In August 2018, the FASB issued ASU 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): ("ASU 2018-15"), relating to a customer’s accounting for implementation, set-up, and other upfront costs incurred in a cloud computing arrangement that is hosted by a vendor. Under the new guidance, a customer will apply the same criteria for capitalizing implementation costs as it would for an arrangement that has a software license. The new guidance does not affect the accounting for the service element of a hosting arrangement that is a service contract. The new guidance also prescribes the balance sheet, income statement and cash flow classification of the capitalized software costs and related amortization expense and requires additional quantitative and qualitative disclosures. ASU 2018-15 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019 for public companies. The Company will adopt this guidance prospectively on January 1, 2020, and it believes the adoption of this guidance will not have a material impact on its Consolidated Financial Statements or related disclosures. ASU 2018-13 - In August 2018, the FASB issued ASU 2018-03, Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement ("ASU 2018-13"). The amendments modify the disclosure requirements in Topic 820. ASU 2018-13 is effective for all entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. The amendments on (i) changes in unrealized gains and losses, (ii) the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements, and (iii) the narrative description of measurement uncertainty should be applied prospectively for only the most recent interim or annual period presented in the initial fiscal year of adoption. All other amendments should be applied retrospectively to all periods presented upon their effective date. The Company will adopt this guidance on January 1, 2020, and it believes the adoption of this guidance will not have a material impact on its Consolidated Financial Statements or related disclosures. ASU 2017-04 - In January 2017, the FASB issued ASU 2017-04, Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment ("ASU 2017-04"). ASU 2017-04 simplifies the recognition and measurement of a goodwill impairment loss by eliminating Step 2 of the quantitative goodwill impairment test. The guidance requires a one-step impairment test in which an entity compares the fair value of a reporting unit with its carrying amount and recognizes an impairment charge for the amount by which the carrying amount exceeds the reporting unit's fair value, if any. ASU 2017-04 is effective for fiscal years beginning after December 15, 2019 and should be applied on a prospective basis. The Company will adopt this guidance on January 1, 2020, and it believes the adoption of this guidance will not have a material impact on its Consolidated Financial Statements or related disclosures. ASU 2016-13 - In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments ("ASU 2016-13"). ASU 2016-13 requires financial assets measured at amortized cost basis to be presented at the net amount expected to be collected and amends guidance on the impairment of financial instruments. ASU 2016-13 is effective for public companies who are SEC filers for fiscal years beginning after December 15, 2019, including interim periods within those years. The Company will adopt this guidance on January 1, 2020, and it believes the adoption of this guidance will not have a material impact on its Consolidated Financial Statements or related disclosures.

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Revenue Disaggregated by Geographical Area

The following table summarizes the Company's net product sales from Galafold^® disaggregated by geographic area:



	For the Year
(in thousands)	2019		2018		2017
U.S.	$	52,478	$	7,223	$	—
Ex-U.S.	129,759		84,022		36,930
Total net product sales	$	182,237	$	91,245	$	36,930

Goodwill and Intangible Assets (Tables)

12 Months Ended

Dec. 31, 2019

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of Changes in IPR&D

The following table represents the changes in IPR&D for the years ended December 31, 2019 and 2018, respectively:



	(in millions)
Balance at December 31, 2017	$	23.0
Change in IPR&D	—
Balance at December 31, 2018	$	23.0
Change in IPR&D	—
Balance at December 31, 2019	$	23.0

Schedule of Changes in Goodwill

The following table represents the changes in Goodwill for the years ended December 31, 2019 and 2018, respectively:



	(in millions)
Balance at December 31, 2017	$	197.8
Change in goodwill	—
Balance at December 31, 2018	$	197.8
Change in goodwill	—
Balance at December 31, 2019	$	197.8

Cash, Cash Equivalents, Marketable Securities, and Restricted Cash (Tables)

12 Months Ended

Dec. 31, 2019

Cash, Cash Equivalents, and Short-term Investments [Abstract]

Schedule of Cash and Available for Sale Securities

Cash, cash equivalents, and marketable securities are classified as current unless mentioned otherwise below and consisted of the following:



	As of December 31, 2019
(in thousands)	Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Cash and cash equivalents	$	142,837	$	—	$	—		$	142,837
Corporate debt securities	145,875		121		(5		)	145,991
Commercial paper	73,659		53		(2		)	73,710
Asset-backed securities	77,731		79		—			77,810
U.S. government agency bonds	11,999		2		(10		)	11,991
Money market	350		—		—			350
Certificates of deposit	51		—		—			51
	$	452,502	$	255	$	(17	)	$	452,740
Included in cash and cash equivalents	$	142,837	$	—	$	—		$	142,837
Included in marketable securities ⁽¹⁾	309,665		255		(17		)	309,903
Total cash, cash equivalents, and marketable securities	$	452,502	$	255	$	(17	)	$	452,740

______________________________

⁽¹⁾As of December 31, 2019, $9.5 million of marketable securities have maturity dates greater than 12 months and are available to convert into cash, if needed.



	As of December 31, 2018
(in thousands)	Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Cash and cash equivalents	$	79,749	$	—	$	—		$	79,749
Corporate debt securities	240,969		7		(250		)	240,726
Commercial paper	115,245		—		(104		)	115,141
Asset-backed securities	68,215		4		(84		)	68,135
Money market	350		—		—			350
Certificates of deposit	51		—		—			51
	$	504,579	$	11	$	(438	)	$	504,152
Included in cash and cash equivalents	$	79,749	$	—	$	—		$	79,749
Included in marketable securities	424,830		11		(438		)	424,403
Total cash, cash equivalents, and marketable securities	$	504,579	$	11	$	(438	)	$	504,152

Schedule of Reconciliation of Cash and Cash Equivalents and Restricted Cash



(in thousands)	December 31, 2019		December 31, 2018		December 31, 2017
Cash and cash equivalents	$	142,837	$	79,749	$	49,060
Restricted cash	3,506		2,626		2,177
Cash, cash equivalents, and restricted cash shown in the Consolidated Statements of Cash Flows	$	146,343	$	82,375	$	51,237

Inventories (Tables)

12 Months Ended

Dec. 31, 2019

Inventory Disclosure [Abstract]

Schedule of Inventories for the Period

The following table summarizes the components of inventories:



(in thousands)	December 31, 2019		December 31, 2018
Raw materials	$	6,544	$	1,291
Work-in-process	3,660		3,485
Finished goods	3,837		3,614
Total inventories	$	14,041	$	8,390

Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2019

Property, Plant and Equipment [Abstract]

Schedule of Property and Equipment

Property and equipment consist of the following:



	December 31,
(in thousands)	2019			2018
Property and equipment consist of the following:
Computer equipment	$	6,185		$	4,691
Computer software	1,607			1,298
Research equipment	14,568			8,445
Furniture and fixtures	5,157			4,876
Leasehold improvements	30,294			7,425
Vehicles	124			209
Land	3,190			—
Construction in progress	4,184			102
Gross property and equipment	65,309			27,046
Less accumulated depreciation	(17,604		)	(15,671		)
Net property and equipment	$	47,705		$	11,375

Accounts Payable, Accrued Expenses, and Other Current Liabilities (Tables)

12 Months Ended

Dec. 31, 2019

Payables and Accruals [Abstract]

Schedule of Accounts Payable and Accrued Expenses

Accounts payable, accrued expenses, and other current liabilities consist of the following:



	December 31,
(in thousands)	2019		2018
Accounts payable	$	21,722	$	6,606
Accrued professional fees	7,832		2,276
Accrued contract manufacturing & contract research costs	17,800		5,890
Accrued compensation and benefits	27,156		21,731
Accrued program fees	17,016		16,674
Accrued royalties	5,196		4,463
Accrued interest	3,679		4,189
Accrued milestones	4,000		9,000
Accrued sales rebates and discounts	5,900		3,636
Accrued taxes	7,300		1,330
Other	2,772		4,830
	$	120,373	$	80,625

Share based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Share-based Payment Arrangement [Abstract]

Schedule of Fair Value of Options

The fair value of the stock options granted is estimated on the date of grant using a Black-Scholes option pricing model with the following weighted-average assumptions:



	Years Ended December 31,
	2019			2018			2017
Expected stock price volatility	74.1		%	78.6		%	82.8		%
Risk free interest rate	2.4		%	2.4		%	2.0		%
Expected life of options (years) ⁽¹⁾	5.68			5.62			6.18
Expected annual dividend per share	$	0.00		$	0.00		$	0.00

______________________________________

⁽¹⁾The average expected life is determined using actual historical data.

Schedule of Stock Options Activity

A summary of the Company's stock options for the year ended December 31, 2019 were as follows:



	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Years	Aggregate Intrinsic Value
	(in thousands)					(in millions)
Options outstanding, December 31, 2016	15,497.5		$	7.37
Granted	3,695.3		$	7.17
Exercised	(2,878.7	)	$	5.67
Forfeited	(1,133.0	)	$	9.55
Options outstanding, December 31, 2017	15,181.1		$	7.48
Granted	2,348.0		$	14.96
Exercised	(1,398.0	)	$	6.54
Forfeited	(313.1	)	$	9.55
Expired	(8.0	)	$	10.76
Options outstanding, December 31, 2018	15,810.0		$	8.63
Granted	4,091.0		$	10.29
Exercised	(1,967.0	)	$	5.83
Forfeited	(879.0	)	$	11.07
Expired	(331.0	)	$	13.38
Options outstanding, December 31, 2019	16,724.0		$	9.15	6.4	$	30.8
Vested and unvested expected to vest, December 31, 2019	16,111.2		$	9.08	6.3	$	30.6
Exercisable at December 31, 2019	10,646.5		$	8.33	5.1	$	27.0

Schedule of Non-Vested RSU Activity under the Plan

A summary of non-vested RSU activity under the Plan for the year ended December 31, 2019 is as follows:



	Number of Share		Weighted Average Grant Date Fair Value		Weighted Average Remaining Years	Aggregate Intrinsic Value
	(in thousands)					(in millions)
Non-vested units as of December 31, 2017	2,575.1		$	5.85
Granted	1,811.9		$	16.11
Vested	(530.0	)	$	6.01
Forfeited	(145.0	)	$	9.65
Non-vested units as of December 31, 2018	3,712.0		$	10.59
Granted	3,526.0		$	10.92
Vested	(921.0	)	$	8.49
Forfeited	(525.0	)	$	10.52
Non-vested units as of December 31, 2019	5,792.0		$	11.18	2.4	$	56.4

Schedule of Equity Compensation Expenses

The following table summarizes information related to compensation expense recognized in the Consolidated Statements of Operations related to the equity awards:



	Years Ended December 31,
(in thousands)	2019		2018		2017
Equity compensation expense recognized in:
Research and development expense	$	17,575	$	11,740	$	10,328
Selling, general, and administrative expense	26,855		17,520		12,773
Total equity compensation expense	$	44,430	$	29,260	$	23,101

Assets and Liabilities Measured at Fair Value (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Summary of Assets and Liabilities Subject to Fair Value Measurements



(in thousands)	Level 2		Total
Assets:
Commercial paper	$	73,710	$	73,710
Asset-back securities	77,810		77,810
Corporate debt securities	145,991		145,991
U.S. Government Agency Bonds	11,991		11,991
Money market funds	4,768		4,768
	$	314,270	$	314,270



(in thousands)	Level 2		Level 3		Total
Liabilities:
Contingent consideration payable	$	—	$	22,681	$	22,681
Deferred compensation plan liability	4,419		—		4,419
	$	4,419	$	22,681	$	27,100



(in thousands)	Level 2		Total
Assets:
Commercial paper	$	115,141	$	115,141
Asset-back securities	68,135		68,135
Corporate debt securities	240,726		240,726
Money market funds	3,082		3,082
	$	427,084	$	427,084



(in thousands)	Level 2		Level 3		Total
Liabilities:
Contingent consideration payable	$	—	$	19,700	$	19,700
Deferred compensation plan liability	2,732		—		2,732
	$	2,732	$	19,700	$	22,432

Schedule of Significant Unobservable Inputs Used in the Valuation of the Contingent Consideration Payable

The following significant unobservable inputs were used in the valuation of the contingent consideration payable of Callidus for the ATB-200 Pompe program:



Contingent Consideration Liability	Fair value as of December 31, 2019		Valuation Technique	Unobservable Input	Range
	(in thousands)
				Discount rate	9.6%
Clinical and regulatory milestones	$	22,390	Probability weighted discounted cash flow	Probability of achievement of milestones	75% - 78%
				Projected year of payments	2021 - 2022

Schedule of Changes in Contingent Consideration Payable

The following table shows the change in the balance of contingent consideration payable for the year ended December 31, 2019 and 2018, respectively:



	Year ended December 31,
(in thousands)	2019			2018
Balance, beginning of the period	$	19,700		$	25,400
Milestones payable, included in accrued expenses	—			(9,000		)
Changes in fair value during the period, included in the Consolidated Statements of Operations	3,297			3,300
Adjustment for contingent consideration paid in stock	(316		)	—
Balance, end of the period	$	22,681		$	19,700

- Definition

Tabular disclosure of financial instruments measured at fair value, including those classified in shareholders' equity measured on a recurring or nonrecurring basis. Disclosures include, but are not limited to, fair value measurements recorded and the reasons for the measurements, level within the fair value hierarchy in which the fair value measurements are categorized and transfers between levels 1 and 2. Nonrecurring fair value measurements are those that are required or permitted in the statement of financial position in particular circumstances.

+ References + Details

Debt (Tables)

12 Months Ended

Dec. 31, 2019

Debt Disclosure [Abstract]

Schedule of Liability Components of the Convertible Notes

The Convertible Notes and Senior Secured Term Loan consist of the following:



	As of December 31,
(in thousands)	2019			2018
Principal	$	152,825		$	400,000
Less: debt discount ⁽¹⁾	(2,974		)	(74,145		)
Less: deferred financing ⁽¹⁾	(346		)	(4,115		)
Net carrying value of the debt	$	149,505		$	321,740

______________________________

⁽¹⁾

Included in the Consolidated Balance Sheets within Convertible Notes and Senior Secured Term Loan and amortized to interest expense over the remaining life of the Convertible Notes and Senior Secured Term Loan using the effective interest rate method.

Components of Total Interest Expense Recognized Related to the Convertible Notes

The following table sets forth interest expense recognized related to the Convertible Notes and Senior Secured Term Loan for the years ended December 31, 2019 and 2018 respectively:



(in thousands)	2019			2018
Contractual interest expense	$	16,483		$	11,426
Amortization of debt discount	$	2,381		$	10,421
Amortization of deferred financing	$	165		$	555
Effective interest rate of the liability component, Convertible debt	10.63		%	10.85		%
Effective interest rate of the liability component, Senior Secured Term Loan	10.16		%	10.48		%

Leases (Tables)

12 Months Ended

Dec. 31, 2019

Leases [Abstract]

Lease Cost

Supplemental balance sheet information related to operating leases was as follows:



(in thousands, except year and discount rate amounts)	December 31, 2019
Operating lease ROU asset	$	33,315

Current portion of the operating lease liabilities	$	7,189
Non-current portion of the operating lease liabilities	53,531
Total operating lease liability	$	60,720

Weighted-average remaining lease terms (years)	18.2
Weighted-average discount rate	13.1		%

Future Minimum Lease Payments, Operating Leases

At December 31, 2019, the future minimum operating lease payments were as follows:



(in thousands)	Operating Lease
2020	$	9,738
2021	10,787
2022	10,459
2023	10,809
2024	10,582
Thereafter	163,266
Total lease payments	215,641
Less lease incentives	(28,939		)
Less imputed interest	(125,982		)
Total operating lease liability	$	60,720

Schedule of Future Minimum Lease Payments

At December 31, 2018, the future minimum operating lease payments were as follows:



(in thousands)	Operating Lease
2019	$	6,244
2020	4,063
2021	3,560
2022	3,371
2023	3,611
Thereafter	10,038
Total lease payments	$	30,887

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Schedule of Income (Loss) before Income Taxes

For financial reporting purposes, income (loss) before income taxes includes the following components:



	Years Ended December 31,
(in thousands)	2019			2018			2017
United States	$	(393,955	)	$	(309,183	)	$	(440,696	)
Foreign	38,045			(39,906		)	(8,425		)
Total	$	(355,910	)	$	(349,089	)	$	(449,121	)

Schedule of Income Tax Expense (Benefit)

Following were the components of income tax expense (benefit) for the years ended December 31, 2019, 2018, and 2017:



(in thousands)	2019			2018			2017
Current
Federal	$	—		$	—		$	—
State	—			6			9
Foreign	2,877			(100		)	2,276
Deferred
Federal	(984		)	—			(150,015		)
State	(1,415		)	—			(17,389		)
Foreign	—			—			—
Total	$	478		$	(94	)	$	(165,119	)

Schedule of Reconciliation of the Statutory Tax Rates and the Effective Tax Rates

A reconciliation of the statutory tax rates and the effective tax rates for the years ended December 31, 2019, 2018 and 2017 are as follows:



	Years Ended December 31,
	2019		2018		2017
Statutory rate	(21	)%	(21	)%	(34	)%
State taxes, net of federal benefit	—		(4	)	(5	)
Nondeductible IPR&D	—		6		(1	)
Contingent consideration	—		1		(18	)
Tax credits	(16	)	(10	)	(2	)
Foreign income tax rate differential	9		2		5
Impact of 2017 Act	—		—		27
Nondeductible debt conversion	(1	)	—		—
Other	—		—		5
Valuation allowance	29		26		(14	)
Net	—	%	—	%	(37	)%

Schedule of Significant Components of the Deferred Tax Assets and Liabilities

The significant components of the deferred tax assets and liabilities are as follows:



	For Years Ended December 31,
(in thousands)	2019			2018
Deferred tax assets
Intellectual property	$	46,521		$	48,339
Amortization/depreciation	2,329			3,732
Research tax credit	141,669			96,509
Net operating loss carry forwards	286,850			248,398
Deferred reimbursement	2,230			4,401
Non-cash stock issue	19,058			16,850
Interest carry forward limitation	2,224			1,032
Other	15,986			10,852
Gross deferred tax assets	516,867			430,113
Deferred tax liabilities
Business acquisition	(5,051		)	(6,465		)
Royalty payable	(46,521		)	(48,339		)
Convertible notes	(653		)	(16,666		)
Advanced R&D payments	(2,611		)	(2,103		)
Other	(725		)	—
Total net deferred tax assets	461,306			356,540
Less: valuation allowance	(466,357		)	(363,005		)
Net deferred tax liability	$	(5,051	)	$	(6,465	)

Basic and Diluted Net Loss per Common Share (Tables)

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

Schedule of Reconciliation of the Numerator and Denominator Used in Computing Basic and Diluted Net Loss Per Common Share

The following table provides a reconciliation of the numerator and denominator used in computing basic and diluted net loss attributable to common stockholders per common share:



	Years Ended December 31,
(in thousands, except per share amounts)	2019			2018			2017
Numerator:
Net loss attributable to common stockholders	$	(356,388	)	$	(348,995	)	$	(284,002	)
Denominator:
Weighted average common shares outstanding — basic and diluted	240,421,001			185,790,021			153,355,144

Schedule of Potential Shares of Common Stock that were Excluded from the Computation as they were Anti-Dilutive Using the Treasury Stock Method

The table below presents potential shares of common stock that were excluded from the computation as they were anti-dilutive using the treasury stock method:



	Year ended December 31,
(in thousands)	2019	2018	2017
Options to purchase common stock	16,724	15,810	15,181
Convertible debt	462	40,850	40,850
Outstanding warrants, convertible to common stock	2,555	2,657	3,110
Unvested restricted stock units	5,792	3,712	2,575
Vested restricted stock units, unissued	186	91	50
Total number of potentially issuable shares	25,719	63,120	61,766

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Schedule of Selected Quarterly Financial Data



	Quarters Ended
(in thousands except per share data)	March 31			June 30			September 30			December 31
2019
Net product sales	$	34,046		$	44,130		$	48,768		$	55,293
Net loss	$	(120,299	)	$	(84,551	)	$	(61,809	)	$	(89,729	)
Basic and diluted net loss per common share ⁽¹⁾	$	(0.56	)	$	(0.36	)	$	(0.24	)	$	(0.35	)
2018
Net product sales	$	16,696		$	21,309		$	20,596		$	32,644
Net loss	$	(49,916	)	$	(61,833	)	$	(159,163	)	$	(78,083	)
Basic and diluted net loss per common share ⁽¹⁾	$	(0.28	)	$	(0.33	)	$	(0.84	)	$	(0.43	)

______________________________

Description of Business (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Jul. 31, 2017	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2018
Corporate Information, Status of Operations and Management Plans
Stock issued from equity financing (in shares)	21.1	18.7
Proceeds from issuance of common stock and warrants, net of issuance costs	$ 243,000	$ 189,000	$ 188,994	$ 294,584	$ 243,037
Exchange agreement, aggregate principal amount		$ 247,200	$ 247,200
Exchange agreement, authorized (in shares)		44.0	44.0
Common stock, par value (in dollars per share)		$ 0.01	$ 0.01	$ 0.01		$ 0.01
Accumulated deficit			$ (1,768,610)	$ (1,412,222)
Underwritten Offering
Corporate Information, Status of Operations and Management Plans
Stock issued (in dollars per share)		$ 10.75

Summary of Significant Accounting Policies - Concentration of Credit Risk (Details) $ in Millions	Dec. 31, 2019 USD ($)
Accounting Policies [Abstract]
Allowance for doubtful accounts receivable	$ 0.1

Summary of Significant Accounting Policies - Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2019
Minimum
Property and Equipment
Estimated useful lives	3 years
Maximum
Property and Equipment
Estimated useful lives	5 years

Summary of Significant Accounting Policies - Revenue by Geographical Area (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Net product sales	$ 55,293	$ 48,768	$ 44,130	$ 34,046	$ 32,644	$ 20,596	$ 21,309	$ 16,696	$ 182,237	$ 91,245	$ 36,930
U.S.
Disaggregation of Revenue [Line Items]
Net product sales									52,478	7,223
Ex-U.S.
Disaggregation of Revenue [Line Items]
Net product sales									$ 129,759	$ 84,022
Largest Customer \| Customer Concentration Risk \| Net product sales
Disaggregation of Revenue [Line Items]
Concentration risk, percentage									22.00%
Largest Customer \| Customer Concentration Risk \| Accounts receivable
Disaggregation of Revenue [Line Items]
Concentration risk, percentage									11.00%

Summary of Significant Accounting Policies - Equity Incentive Plan and Stock-Based Compensation (Details)	Dec. 31, 2019 program
Equity-based Compensation
Number of equity-based employee compensation plans	3

Summary of Significant Accounting Policies - Segment Information and Recent Accounting Policies (Details)	12 Months Ended
	Dec. 31, 2019 unit segment
Accounting Policies [Abstract]
Number of business segments \| segment	1
Number of reporting units \| unit	1

Summary of Significant Accounting Policies - Recent Accounting Policies (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle
Operating lease liability	$ 60,720
Operating lease ROU asset	$ 33,315
ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle
Operating lease liability		$ 17,600
Operating lease ROU asset		$ 17,600

Acquisitions (Details) $ in Thousands	1 Months Ended			3 Months Ended			12 Months Ended
Acquisitions (Details) $ in Thousands	Sep. 30, 2018 USD ($) program	Apr. 30, 2017 USD ($)	Jul. 31, 2016 USD ($) shares	Mar. 31, 2019 USD ($)	Sep. 30, 2017 USD ($)	Mar. 31, 2017	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Acquisitions
Number of gene therapy programs for neurologic LSDs developed \| program	10
Milestone payment				$ 9,000
Loss on impairment of assets							$ 0	$ 0	$ 465,427
Changes in fair value of contingent consideration payable							3,297	3,300	(234,322)
Contingent consideration payable							22,681	19,700
Milestone Payment \| Callidus
Acquisitions
Milestone payment				$ 9,000
Fixed assets
Acquisitions
Loss on impairment of assets									1,700
MiaMed Inc
Acquisitions
Asset acquisition, total consideration, stock and cash			$ 6,500
Asset acquisition, cash consideration paid			1,800
Asset acquisition, potential aggregate deal value			$ 89,500
Charges to research expense for stock issued in asset acquisition										$ 6,500
MiaMed Inc \| Amicus \| Common Stock
Acquisitions
Consideration paid in common stock (in shares) \| shares			825,603
Scioderm
Acquisitions
Enrollment rate						100.00%
Milestone payment		$ 10,000
Loss on impairment of assets									$ 463,700
Changes in fair value of contingent consideration payable					$ 254,700
Selling , general and administrative costs due to wind-down					400
Research and development expenses due to wind-down					8,100
Income tax benefit due to wind-down					$ 164,700
Callidus
Acquisitions
Contingent consideration payable							22,700
Callidus \| Changes in fair value of contingent consideration payable
Acquisitions
Changes in fair value of contingent consideration payable							$ 3,300
Clinical, Regulatory and Commercial milestones \| MiaMed Inc \| Maximum
Acquisitions
Contingent consideration payable upon achievement of milestones			$ 83,000
Celenex
Acquisitions
Research and development expense	$ 100,000							$ 100,000
Contingent consideration based on the achievement of certain milestones	15,000
Contingent consideration based on the achievement of regulatory milestones	262,000
Maximum payment under contingent consideration	75,000
Celenex \| Nationwide Children's Hospital
Acquisitions
Contingent consideration based on the achievement of certain milestones	$ 7,800

Goodwill and Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Changes in IPR&D
Beginning balance	$ 23,000	$ 23,000
Change in IPR&D	0	0	$ 463,700
Ending balance	23,000	23,000	$ 23,000
Changes in goodwill
Beginning balance	197,797
Change in goodwill	0	0
Ending balance	$ 197,797	$ 197,797

Goodwill and Intangible Assets - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible assets other than goodwill	$ 23,000	$ 23,000	$ 23,000	$ 486,700
Goodwill	197,797	197,797		$ 197,800
Loss of impairment of intangible assets	$ 0	$ 0	$ 463,700

Cash, Cash Equivalents, Marketable Securities, and Restricted Cash - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Cash and cash equivalents	$ 142,837,000	$ 79,749,000	$ 49,060,000
Debt securities, available-for-sale	309,903,000	424,403,000
Debt securities, realized gain (loss)	0	0
Fair value of available-for-sale debt securities in unrealized loss positions	$ 42,600,000	$ 403,100,000

Cash, Cash Equivalents, Marketable Securities, and Restricted Cash - Cash and Available for Sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	$ 142,837	$ 79,749	$ 49,060
Cost, debt securities	309,665	424,830
Cost, cash balances and debt securities	452,502	504,579
Gross Unrealized Gain	255	11
Gross Unrealized Loss	(17)	(438)
Fair value, cash balances	142,837	79,749
Debt securities, available-for-sale	309,903	424,403
Fair value, cash balances and debt securities	452,740	504,152
Marketable securities with maturity date greater than 12 months	9,500
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Cost, debt securities	145,875	240,969
Gross Unrealized Gain	121	7
Gross Unrealized Loss	(5)	(250)
Debt securities, available-for-sale	145,991	240,726
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Cost, debt securities	73,659	115,245
Gross Unrealized Gain	53	0
Gross Unrealized Loss	(2)	(104)
Debt securities, available-for-sale	73,710	115,141
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Cost, debt securities	77,731	68,215
Gross Unrealized Gain	79	4
Gross Unrealized Loss	0	(84)
Debt securities, available-for-sale	77,810	68,135
U.S. government agency bonds
Debt Securities, Available-for-sale [Line Items]
Cost, debt securities	11,999
Gross Unrealized Gain	2
Gross Unrealized Loss	(10)
Debt securities, available-for-sale	11,991
Money market
Debt Securities, Available-for-sale [Line Items]
Cost, debt securities	350	350
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Debt securities, available-for-sale	350	350
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Cost, debt securities	51	51
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Debt securities, available-for-sale	$ 51	$ 51

Cash, Cash Equivalents, Marketable Securities, and Restricted Cash - Reconciliation of Cash and Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Cash and cash equivalents	$ 142,837	$ 79,749	$ 49,060
Restricted cash	3,506	2,626	2,177
Cash, cash equivalents, and restricted cash shown in the Consolidated Statements of Cash Flows	$ 146,343	$ 82,375	$ 51,237	$ 187,413

Inventories (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Inventory Disclosure [Abstract]
Raw materials	$ 6,544	$ 1,291
Work-in-process	3,660	3,485
Finished goods	3,837	3,614
Total inventories	14,041	8,390
Reserve for inventory	$ 200	$ 200

Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property and Equipment
Property and equipment, gross	$ 65,309	$ 27,046
Less accumulated depreciation	(17,604)	(15,671)
Property and equipment, net	47,705	11,375
Depreciation and amortization	4,500	4,200
Computer equipment
Property and Equipment
Property and equipment, gross	6,185	4,691
Computer software
Property and Equipment
Property and equipment, gross	1,607	1,298
Research equipment
Property and Equipment
Property and equipment, gross	14,568	8,445
Furniture and fixtures
Property and Equipment
Property and equipment, gross	5,157	4,876
Leasehold improvements
Property and Equipment
Property and equipment, gross	30,294	7,425
Vehicles
Property and Equipment
Property and equipment, gross	124	209
Land
Property and Equipment
Property and equipment, gross	3,190	0
Construction in progress
Property and Equipment
Property and equipment, gross	$ 4,184	$ 102

Accounts Payable, Accrued Expenses, and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accounts payable and accrued expenses
Accounts payable	$ 21,722	$ 6,606
Accrued professional fees	7,832	2,276
Accrued contract manufacturing & contract research costs	17,800	5,890
Accrued compensation and benefits	27,156	21,731
Accrued program fees	17,016	16,674
Accrued royalties	5,196	4,463
Accrued interest	3,679	4,189
Accrued milestones	4,000	9,000
Accrued sales rebates and discounts	5,900	3,636
Accrued taxes	7,300	1,330
Other	2,772	4,830
Accounts payable and accrued expenses	$ 120,373	$ 80,625

Stockholders' Equity - Common Stock and Warrants (Details) $ / shares in Units, $ in Thousands			1 Months Ended				3 Months Ended		12 Months Ended
	Feb. 16, 2018 shares	Feb. 15, 2018 shares	Mar. 31, 2019 USD ($) $ / shares shares	Apr. 30, 2018 USD ($) $ / shares shares	Feb. 28, 2018 USD ($) $ / shares shares	Jul. 31, 2017 USD ($) $ / shares shares	Jun. 30, 2019 USD ($) $ / shares shares	Mar. 31, 2019 USD ($) $ / shares	Dec. 31, 2019 USD ($) vote $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) shares	Jun. 30, 2018 $ / shares shares	Jun. 07, 2018 shares
Convertible Debt
Common stock, shares authorized (in shares) \| shares									500,000,000	500,000,000	250,000,000	500,000,000	500,000,000
Voting right for each share held, number \| vote									1
Stock issued from equity financing (in shares) \| shares						21,100,000	18,700,000
Gross cash proceeds from warrant exercises									$ 812	$ 3,617	$ 0
Net proceeds from the issuance of common stock after deducting underwriting discounts and commissions						$ 243,000	$ 189,000		$ 188,994	$ 294,584	$ 243,037
Contingent consideration, milestone payment								$ 9,000
Milestone payment, stock issued as consideration								$ 9,000
Common stock, par value (in dollars per share) \| $ / shares							$ 0.01		$ 0.01	$ 0.01		$ 0.01
Exchange agreement, aggregate principal amount							$ 247,200		$ 247,200
Exchange agreement, authorized (in shares) \| shares							44,000,000.0		44,000,000.0
Price per share of common stock issued (in dollars per share) \| $ / shares						$ 12.25
Warrants
Convertible Debt
Stock issued from equity financing (in shares) \| shares			101,787	453,214
Gross cash proceeds from warrant exercises			$ 800	$ 3,600
Underwritten Offering
Convertible Debt
Stock issued (in dollars per share) \| $ / shares							$ 10.75
Common Stock
Convertible Debt
Stock issued from equity financing (in shares) \| shares	885,000	19,400,000			20,200,000
Net proceeds from the issuance of common stock after deducting underwriting discounts and commissions					$ 294,600
Price per share of common stock issued (in dollars per share) \| $ / shares					$ 15.50
Common Stock \| Warrants
Convertible Debt
Exercise price of warrants (in dollars per share) \| $ / shares			$ 7.98	$ 7.98				$ 7.98
Common Stock
Convertible Debt
Stock issued from equity financing (in shares) \| shares									18,720,930	20,239,839	21,122,449
Milestone payment, stock issued as consideration								$ 9,300

Stockholders' Equity - Nonqualified Cash Plan and Equity Incentive Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Stockholders' Equity
Deferred compensation investment	$ 4.4	$ 2.7
2007 Plan and 2007 Director Plan
Stockholders' Equity
Award term	P10Y
Vesting percentage	100.00%
2007 Plan and 2007 Director Plan \| First Anniversary
Stockholders' Equity
Vesting percentage	25.00%
Maximum \| 2007 Plan and 2007 Director Plan \| Options to purchase common stock
Stockholders' Equity
Number of shares reserved for issuance	10,667,216

Share based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Dec. 21, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from exercise of stock options		$ 11,476	$ 9,144	$ 16,301
RSUs vested and non-vested units expected to vest (in shares)		920,782
Unvested restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period following separation for accelerated vesting	2 years
Unvested restricted stock units \| Stock Option Plan Amended Restated 2007 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs, period for recognition (in years)		2 years 4 months 24 days
RSUs vested and non-vested units expected to vest (in shares)		921,000.0	530,000.0
Unrecognized compensation cost		$ 39,800
Options to purchase common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value, options (in dollars per share)		$ 6.67	$ 10.19	$ 5.09
Aggregate intrinsic value of options exercised		$ 11,800	$ 11,900	$ 20,800
Proceeds from exercise of stock options		11,500	$ 9,100	$ 16,300
Total unrecognized compensation costs		$ 32,400
Unrecognized compensation costs, period for recognition (in years)		2 years 6 months

Share based Compensation - Weighted-average Assumptions (Details) - Options to purchase common stock - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected stock price volatility	74.10%	78.60%	82.80%
Risk free interest rate	2.40%	2.40%	2.00%
Expected life of options (years)	5 years 8 months 4 days	5 years 7 months 13 days	6 years 2 months 4 days
Expected annual dividend per share	$ 0.00	$ 0.00	$ 0.00

Share based Compensation - Stock Option Activity (Details) - Options to purchase common stock - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Number of Shares
Balance at the beginning of the period (in shares)	15,810,000.0	15,181,100	15,497,500
Options, Granted (in shares)	4,091,000.0	2,348,000.0	3,695,300
Options, Exercised (in shares)	(1,967,000.0)	(1,398,000.0)	(2,878,700)
Options, Forfeited (in shares)	(879,000.0)	(313,100)	(1,133,000.0)
Options, Expired (in shares)	(331,000.0)	(8,000.0)
Balance at the end of the period (in shares)	16,724,000.0	15,810,000.0	15,181,100
Vested and unvested expected to vest as of the end of the period (in shares)	16,111,200
Exercisable at the end of the period (in shares)	10,646,500
Weighted Average Exercise Price
Balance at the beginning of the period (in dollars per share)	$ 8.63	$ 7.48	$ 7.37
Options, Granted (in dollars per share)	10.29	14.96	7.17
Options, Exercised (in dollars per share)	5.83	6.54	5.67
Options, Forfeited (in dollars per share)	11.07	9.55	9.55
Options, Expired (in dollars per share)	13.38	10.76
Balance at the end of the period (in dollars per share)	9.15	$ 8.63	$ 7.48
Vested and unvested expected to vest as of the end of the period (in dollars per share)	9.08
Exercisable at the end of the period (in dollars per share)	$ 8.33
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Balance at the end of the period	6 years 4 months 24 days
Vested and unvested expected to vest at the end of the period	6 years 3 months 18 days
Exercisable at the end of the period	5 years 1 month 6 days
Aggregate intrinsic value of options outstanding	$ 30.8
Aggregate intrinsic value of options vested and unvested expected to vest	30.6
Aggregate intrinsic value of options exercisable	$ 27.0

Share based Compensation - RSUs and PBRSUs Summary (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Number of Share
Vested (in shares)	(920,782)
Stock Option Plan Amended Restated 2007 Equity Incentive Plan \| Unvested restricted stock units
Number of Share
Non-vested units as of the beginning of the period (in shares)	3,712,000.0	2,575,100
Granted (in shares)	3,526,000.0	1,811,900
Vested (in shares)	(921,000.0)	(530,000.0)
Forfeited (in shares)	(525,000.0)	(145,000.0)
Non-vested units as of the end of the period (in shares)	5,792,000.0	3,712,000.0
Weighted Average Grant Date Fair Value
Non-vested units as of the beginning of the period (in dollars per share)	$ 10.59	$ 5.85
Granted (in dollars per share)	10.92	16.11
Vested (in dollars per share)	8.49	6.01
Forfeited (in dollars per share)	10.52	9.65
Non-vested units as of the end of the period (in dollars per share)	$ 11.18	$ 10.59
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Non-vested units, weighted average remaining years	2 years 4 months 24 days
Non-vested units, aggregate intrinsic value	$ 56.4

Share based Compensation - Expense Summary (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total equity compensation expense	$ 44,430	$ 29,260	$ 23,101
Research and development expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total equity compensation expense	17,575	11,740	10,328
Selling, general, and administrative expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total equity compensation expense	$ 26,855	$ 17,520	$ 12,773

- Assets and Liabilities (Details) $ in Thousands	3 Months Ended
- Assets and Liabilities (Details) $ in Thousands	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Assets:
Fair value of assets		$ 314,270	$ 427,084
Liabilities:
Contingent consideration payable		22,681	19,700
Deferred compensation plan liability		4,419	2,732
Fair value of liabilities		27,100	22,432
Milestone payment, stock issued as consideration	$ 9,000
Callidus
Liabilities:
Contingent consideration payable		22,700
ATB-200 Pompe Program \| Clinical and Regulatory Approval Milestones \| Callidus
Liabilities:
Contingent consideration payable		$ 22,390
ATB-200 Pompe Program \| Minimum \| Clinical and Regulatory Approval Milestones \| Callidus \| Probability of Milestone Achievement
Liabilities:
Contingent consideration, measurement input		0.750
ATB-200 Pompe Program \| Maximum \| Clinical and Regulatory Approval Milestones \| Callidus \| Probability of Milestone Achievement
Liabilities:
Contingent consideration, measurement input		0.780
Convertible Notes \| 2016 Convertible Notes
Liabilities:
Fair value of the debt		$ 5,000
Commercial paper
Assets:
Fair value of assets		73,710	115,141
Asset-backed securities
Assets:
Fair value of assets		77,810	68,135
Corporate debt securities
Assets:
Fair value of assets		145,991	240,726
U.S. government agency bonds
Assets:
Fair value of assets		11,991
Money market
Assets:
Fair value of assets		4,768	3,082
Level 2
Assets:
Fair value of assets		314,270	427,084
Liabilities:
Contingent consideration payable		0	0
Deferred compensation plan liability		4,419	2,732
Fair value of liabilities		4,419	2,732
Level 2 \| Commercial paper
Assets:
Fair value of assets		73,710	115,141
Level 2 \| Asset-backed securities
Assets:
Fair value of assets		77,810	68,135
Level 2 \| Corporate debt securities
Assets:
Fair value of assets		145,991	240,726
Level 2 \| U.S. government agency bonds
Assets:
Fair value of assets		11,991
Level 2 \| Money market
Assets:
Fair value of assets		4,768	3,082
Level 3
Liabilities:
Contingent consideration payable		22,681	19,700
Deferred compensation plan liability		0	0
Fair value of liabilities		$ 22,681	$ 19,700
Level 3 \| ATB-200 Pompe Program \| Clinical and Regulatory Approval Milestones \| Probability Weighted Discounted Cash Flow \| Callidus \| Discount Rate
Liabilities:
Contingent consideration, measurement input		0.096
Common Stock
Liabilities:
Milestone payment, stock issued as consideration	$ 9,300

Assets and Liabilities Measured at Fair Value - Level 3 Roll Forward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of the period	$ 19,700	$ 25,400
Milestones payable, included in accrued expenses	0	(9,000)
Changes in fair value during the period, included in the Consolidated Statements of Operations	3,297	3,300	$ (234,322)
Adjustment for contingent consideration paid in stock	(316)	0
Balance, end of the period	$ 22,681	$ 19,700	$ 25,400

Debt - Narrative (Details)			1 Months Ended				3 Months Ended	6 Months Ended	12 Months Ended
Debt - Narrative (Details)	Feb. 16, 2018 shares	Feb. 15, 2018 USD ($) shares	Sep. 30, 2018 USD ($)	Feb. 28, 2018 shares	Jul. 31, 2017 shares	Dec. 31, 2016 USD ($) day $ / shares shares	Jun. 30, 2019 USD ($) $ / shares shares	Jun. 30, 2019 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) day $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) shares	Jun. 30, 2018 $ / shares shares	Jun. 07, 2018 USD ($) shares
Convertible Debt
Common stock issued from underwriting agreement (in shares) \| shares					21,100,000		18,700,000
Fair value of derivative liability		$ 507,400,000											$ 88,300,000
Fair value of derivative asset		$ 13,600,000
Change in fair value of derivatives										$ (2,700,000)
Common stock, shares authorized (in shares) \| shares									500,000,000	500,000,000	250,000,000	500,000,000	500,000,000
Exchange agreement, aggregate principal amount							$ 247,200,000	$ 247,200,000	$ 247,200,000
Exchange agreement, authorized (in shares) \| shares							44,000,000.0	44,000,000.0	44,000,000.0
Common stock, par value (in dollars per share) \| $ / shares							$ 0.01	$ 0.01	$ 0.01	$ 0.01		$ 0.01
Accrued and unpaid interest on exchange agreement								$ 1,300,000
Gain (loss) on extinguishment of debt, additional paid-in capital									$ 215,000,000.0
Gain (loss) on extinguishment of debt, fair value of common shares issued									400,000
Loss on exchange of convertible debt									40,624,000	$ 0	$ 0
Proceeds from capped call confirmations, exchange of convertible debt								$ 19,900,000	$ (19,875,000)	$ 0	$ 0
Common Stock Capped Call Confirmation
Convertible Debt
Capped call confirmations, initial cap price (in dollars per share) \| $ / shares									$ 7.20
Capped call confirmations, premium percentage									50.00%
Common Stock
Convertible Debt
Common stock issued from underwriting agreement (in shares) \| shares	885,000	19,400,000		20,200,000
Over-allotment Option \| Common Stock
Convertible Debt
Number of days granted underwriters for purchase of shares		30 days
Maximum number of additional shares granted to underwriters (in shares) \| shares	2,900,000
Convertible Notes \| Common Stock Capped Call Confirmation
Convertible Debt
Fair value of derivative asset													$ 2,400,000
Convertible Notes \| 2016 Convertible Notes
Convertible Debt
Aggregate principal amount						$ 250,000,000
Net proceeds after deducting fees and estimated expenses						243,000,000.0
Proceeds for capped call confirmations						$ 13,500,000
Shares issued per increment of convertible debt (in shares) \| shares						40,800,000
Debt conversion ratio (in shares)						0.1633987
Conversion price (in dollars per share) \| $ / shares						$ 6.12
Threshold consecutive trading days \| day						30			30
Threshold percentage						130.00%			130.00%
Period following 5 consecutive trading day period, trading price less than 98% of product of sales price						5 days
Period following issuance of stock rights options or warrants with price per share less than last reported sales price						60 days
Period for measurement of sales price						10 days
Excess of value per share for triggering event, percent						10.00%
Convertible Notes \| 2016 Convertible Notes \| Minimum
Convertible Debt
Threshold trading days						20 days			20 days
Convertible Notes \| 2016 Convertible Notes \| Over-allotment Option \| Private Placement Purchase Agreement
Convertible Debt
Aggregate principal amount						$ 25,000,000
Line of Credit
Debt Instruments
New credit facility borrowing capacity			$ 150,000,000
Debt instrument term			5 years
Periodic payment, percentage			12.50%
Proceeds from issuance of debt			$ 146,600,000
Line of Credit \| LIBOR
Debt Instruments
Basis spread on variable rate			7.50%

Debt - Convertible Notes and Senior Secured Term Loan (Details) - Convertible Notes - 2016 Convertible Notes - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Instruments
Principal	$ 152,825	$ 400,000
Less: debt discount	(2,974)	(74,145)
Less: deferred financing	(346)	(4,115)
Net carrying value of the debt	$ 149,505	$ 321,740

Debt - Interest Expense (Details) - USD ($) $ in Thousands	12 Months Ended
Debt - Interest Expense (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Convertible Notes \| 2016 Convertible Notes
Interest expense
Contractual interest expense	$ 16,483	$ 11,426
Amortization of debt discount	2,381	10,421
Amortization of deferred financing	$ 165	$ 555
Effective interest rate of the liability component	10.63%	10.85%
Senior Notes
Interest expense
Effective interest rate of the liability component	10.16%	10.48%

Leases (Details) - USD ($) $ in Thousands	12 Months Ended
Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Leases [Abstract]
Operating lease cost	$ 10,800
Cash paid for amounts included in operating lease liabilities	4,900
Right-of-use assets obtained in exchange for new operating lease liabilities	21,800
Operating lease ROU asset	33,315
Current portion of the operating lease liabilities	7,189
Non-current portion of the operating lease liabilities	53,531
Total operating lease liability	$ 60,720
Weighted-average remaining lease terms (years)	18 years 2 months 12 days
Weighted-average discount rate	13.10%
Operating Lease
2020	$ 9,738
2021	10,787
2022	10,459
2023	10,809
2024	10,582
Thereafter	163,266
Total lease payments	215,641
Less lease incentives	(28,939)
Less imputed interest	(125,982)
Total operating lease liability	60,720
Minimum lease payments
2019		$ 6,244
2020		4,063
2021		3,560
2022		3,371
2023		3,611
Thereafter		10,038
Total lease payments		30,887
Rent expense, including fees for utilities and common area maintenances		5,700	$ 3,900
Tenant improvements paid through lease incentive	$ 19,388	$ 0	$ 0

Income Taxes - Statutory Rate (Details) - USD ($)		12 Months Ended
Income Taxes - Statutory Rate (Details) - USD ($)	Dec. 22, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income (loss) before income taxes:
United States		$ (393,955,000)	$ (309,183,000)	$ (440,696,000)
Foreign		38,045,000	(39,906,000)	(8,425,000)
Loss before income tax		(355,910,000)	(349,089,000)	(449,121,000)
Current
Federal		0	0	0
State		0	6,000	9,000
Foreign		2,877,000	(100,000)	2,276,000
Deferred
Federal		(984,000)	0	(150,015,000)
State		(1,415,000)	0	(17,389,000)
Foreign		0	0	0
Income tax expense (benefit)		$ 478,000	$ (94,000)	$ (165,119,000)
Reconciliation of the statutory tax rates and the effective tax rates
Statutory rate	(21.00%)	(21.00%)	(21.00%)	(34.00%)
State taxes, net of federal benefit		0.00%	(4.00%)	(5.00%)
Nondeductible IPR&D		0.00%	6.00%	(1.00%)
Contingent consideration		0.00%	1.00%	(18.00%)
Tax credits		(16.00%)	(10.00%)	(2.00%)
Foreign income tax rate differential		9.00%	2.00%	5.00%
Impact of 2017 Act		0.00%	0.00%	27.00%
Nondeductible debt conversion		(1.00%)	0.00%	0.00%
Other		0.00%	0.00%	5.00%
Valuation allowance		29.00%	26.00%	(14.00%)
Net		0.00%	0.00%	(37.00%)
Accrual for interest and penalties		$ 0
Accrual for uncertain tax positions		0
Current federal and state tax expense (benefit)		$ (2,400,000)

Income Taxes - Deferred and Valuation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets
Intellectual property	$ 46,521	$ 48,339
Amortization/depreciation	2,329	3,732
Research tax credit	141,669	96,509
Net operating loss carry forwards	286,850	248,398
Deferred reimbursement	2,230	4,401
Non-cash stock issue	19,058	16,850
Interest carry forward limitation	2,224	1,032
Other	15,986	10,852
Gross deferred tax assets	516,867	430,113
Deferred tax liabilities
Business acquisition	(5,051)	(6,465)
Royalty payable	(46,521)	(48,339)
Convertible notes	(653)	(16,666)
Advanced R&D payments	(2,611)	(2,103)
Other	(725)	0
Total net deferred tax assets	461,306	356,540
Less: valuation allowance	(466,357)	(363,005)
Net deferred tax liability	(5,051)	$ (6,465)
Increase in the valuation allowance	$ 103,400

Income Taxes - Loss Carryforwards (Details) $ in Millions	Dec. 31, 2019 USD ($)
Research and experimentation tax credit carryforward
Operating Loss Carryforwards [Line Items]
Tax credit carryforward amount	$ 27.6
Orphan drug tax credit carryforwards
Operating Loss Carryforwards [Line Items]
Tax credit carryforward amount	114.0
Federal
Operating Loss Carryforwards [Line Items]
Amount of net operating loss carry forwards	1,036.0
State
Operating Loss Carryforwards [Line Items]
Amount of net operating loss carry forwards	897.8
Foreign
Operating Loss Carryforwards [Line Items]
Amount of net operating loss carry forwards	$ 30.6

Collaborative Agreements (Details)	1 Months Ended		3 Months Ended								12 Months Ended
Collaborative Agreements (Details)	Oct. 31, 2018 USD ($)	Nov. 30, 2013 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Collaborative Agreements
Revenue recognized			$ 55,293,000	$ 48,768,000	$ 44,130,000	$ 34,046,000	$ 32,644,000	$ 20,596,000	$ 21,309,000	$ 16,696,000	$ 182,237,000	$ 91,245,000	$ 36,930,000
Deferred reimbursements			8,906,000				10,156,000				8,906,000	10,156,000
Accounts payable, accrued expenses, and other current liabilities			120,373,000				$ 80,625,000				120,373,000	$ 80,625,000
Collaborative Arrangements
Collaborative Agreements
Conditional aggregate payments per indication	$ 86,500,000
Collaboration Agreement, Discovery Program Fee			10,000,000.0								10,000,000.0
Payments for collaborative agreement	$ 7,000,000
Collaborative Arrangements \| GSK
Collaborative Agreements
Payments for collaborative agreement											1,500,000
Accrued payments for collaborative arrangement			4,000,000.0								4,000,000.0
Revised Agreement \| GSK
Collaborative Agreements
Upfront payment received		$ 0
Potential milestone payments upon achievement of post-approval and sales-based milestones		$ 40,000,000
Number of major markets outside the U.S. from whom parties to contractual arrangement is eligible to receive post-approval and sales-based milestones		8
Revenue recognized											15,500,000
Deferred reimbursements			10,200,000								10,200,000
Accounts payable, accrued expenses, and other current liabilities			$ 5,200,000								$ 5,200,000

Basic and Diluted Net Loss per Common Share (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net loss attributable to common stockholders	$ (89,729)	$ (61,809)	$ (84,551)	$ (120,299)	$ (78,083)	$ (159,163)	$ (61,833)	$ (49,916)	$ (356,388)	$ (348,995)	$ (284,002)
Denominator:
Weighted-average common shares outstanding - basic and diluted (in shares)									240,421,001	185,790,021	153,355,144
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)									25,719,000	63,120,000	61,766,000
Options to purchase common stock
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)									16,724,000	15,810,000	15,181,000
Convertible debt
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)									462,000	40,850,000	40,850,000
Outstanding warrants, convertible to common stock
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)									2,555,000	2,657,000	3,110,000
Unvested restricted stock units
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)									5,792,000	3,712,000	2,575,000
Vested restricted stock units, unissued
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)									186,000	91,000	50,000

Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Selected Quarterly Financial Data
Net product sales	$ 55,293	$ 48,768	$ 44,130	$ 34,046	$ 32,644	$ 20,596	$ 21,309	$ 16,696	$ 182,237	$ 91,245	$ 36,930
Net loss	$ (89,729)	$ (61,809)	$ (84,551)	$ (120,299)	$ (78,083)	$ (159,163)	$ (61,833)	$ (49,916)	$ (356,388)	$ (348,995)	$ (284,002)
Basic and diluted net loss per common share (in dollars per share)	$ (0.35)	$ (0.24)	$ (0.36)	$ (0.56)	$ (0.43)	$ (0.84)	$ (0.33)	$ (0.28)	$ (1.48)	$ (1.88)	$ (1.85)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details