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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2019	Jul. 30, 2019
Cover page.
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 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 each class	Common Stock
Trading Symbol	FOLD
Security Exchange Name	NASDAQ
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 Common Stock, Shares Outstanding		254,626,063
Entity Central Index Key	0001178879
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Amendment Flag	false

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 220,578	$ 79,749
Investments in marketable securities	355,078	424,403
Accounts receivable	28,709	21,962
Inventories	10,395	8,390
Prepaid expenses and other current assets	20,116	16,592
Total current assets	634,876	551,096
Operating lease right-of-use assets, less accumulated amortization of $2,641 and $0 at June 30, 2019 and December 31, 2018, respectively	35,052
Property and equipment, less accumulated depreciation of $16,890 and $15,671 at June 30, 2019 and December 31, 2018, respectively	15,273	11,375
In-process research & development	23,000	23,000
Goodwill	197,797	197,797
Other non-current assets	12,035	6,683
Total Assets	918,033	789,951
Current liabilities:
Accounts payable, accrued expenses, and other current liabilities	84,119	80,625
Deferred reimbursements	2,750	5,500
Operating lease liabilities	2,678
Total current liabilities	89,547	86,125
Deferred reimbursements	11,406	10,156
Convertible notes	2,070	175,006
Senior secured term loan	146,994	146,734
Contingent consideration payable	21,247	19,700
Deferred income taxes	6,465	6,465
Operating lease liabilities	36,259
Other non-current liabilities	3,987	2,853
Total liabilities	317,975	447,039
Commitments and contingencies
Stockholders’ equity:
Common stock, $0.01 par value, 500,000,000 shares authorized, 254,513,522 and 189,383,924 shares issued and outstanding at June 30, 2019 and December 31, 2018, respectively	2,589	1,942
Additional paid-in capital	2,201,447	1,740,061
Accumulated other comprehensive loss:
Foreign currency translation adjustment	352	495
Unrealized gain on available-for-sale securities	355	(427)
Warrants	12,387	13,063
Accumulated deficit	(1,617,072)	(1,412,222)
Total stockholders’ equity	600,058	342,912
Total Liabilities and Stockholders’ Equity	$ 918,033	$ 789,951

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Less accumulated depreciation and amortization on finance and operating lease right-of-use leases	$ 2,641	$ 0
Accumulated depreciation of property and equipment	$ 16,890	$ 15,671
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	254,513,522	189,383,924
Common stock, shares outstanding	254,513,522	189,383,924

Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue:
Net product sales	$ 44,130	$ 21,309	$ 78,176	$ 38,005
Cost of goods sold	5,367	3,135	9,422	5,750
Gross profit	38,763	18,174	68,754	32,255
Operating expenses:
Research and development	70,981	34,660	135,574	75,458
Selling, general and administrative	42,578	29,172	86,881	56,568
Changes in fair value of contingent consideration payable	480	300	1,863	1,400
Depreciation and amortization	1,154	973	2,145	1,942
Total operating expenses	115,193	65,105	226,463	135,368
Loss from operations	(76,430)	(46,931)	(157,709)	(103,113)
Other income (expense):
Interest income	2,599	2,913	5,238	4,650
Interest expense	(4,625)	(4,560)	(11,079)	(9,048)
Loss on exchange of convertible notes	(4,501)	0	(40,624)	0
Change in fair value of derivatives	0	(7,600)	0	(2,739)
Other (expense) income	(877)	(5,316)	209	(2,554)
Loss before income tax	(83,834)	(61,494)	(203,965)	(112,804)
Income tax benefit	(717)	(339)	(885)	1,053
Net loss attributable to common stockholders	$ (84,551)	$ (61,833)	$ (204,850)	$ (111,751)
Net loss attributable to common stockholders per common share - basic and diluted (in dollars per share)	$ (0.36)	$ (0.33)	$ (0.91)	$ (0.61)
Weighted-average common shares outstanding - basic and diluted (in shares)	238,089,824	188,621,423	225,848,013	182,303,128

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net loss	$ (84,551)	$ (61,833)	$ (204,850)	$ (111,751)
Other comprehensive (loss) gain:
Foreign currency translation adjustment gain (loss), net of tax impact of $(30), $(109), $(30) and $(109), respectively	1,881	2,308	77	503
Unrealized (loss) gain on available-for-sale securities, net of tax impact of $(220), $0, $(220) and $0, respectively	(22)	422	562	(19)
Other comprehensive income (loss)	1,859	2,730	639	484
Comprehensive loss	$ (82,692)	$ (59,103)	$ (204,211)	$ (111,267)

- 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	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Foreign currency translation adjustment, tax (expense) benefit	$ (30)	$ (109)	$ (30)	$ (109)
Available-for-sale securities, tax expense (benefit)	$ (220)	$ 0	$ (220)	$ 0

Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Outstanding warrants, convertible to common stock	Other Comprehensive Gain (Loss)	Accumulated Deficit
Increase (Decrease) in Stockholders' Equity
Reclassification upon ASU 2018-02 adoption	$ 0				$ (383)	$ 383
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)		560,721
Stock issued from exercise of stock options, net	3,978	$ 6	3,972
Stock issued from equity financing (in shares)		20,239,839
Stock issued from equity financing	294,584	$ 202	294,382
Restricted stock tax vesting (in shares)		181,868
Restricted stock tax vesting	(1,912)		(1,912)
Stock-based compensation	7,478		7,478
Change in fair value of derivatives	(83,199)		(83,199)
Unrealized holding gain (loss) on available-for-sale securities	(441)				(441)
Foreign currency translation adjustment	(1,805)				(1,805)
Net loss	(49,916)					(49,916)
Balance (in shares) at Mar. 31, 2018		187,972,218
Balance at Mar. 31, 2018	521,617	$ 1,929	1,621,479	16,076	(4,724)	(1,113,143)
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
Unrealized holding gain (loss) on available-for-sale securities	(19)
Foreign currency translation adjustment	503
Net loss	(111,751)
Balance (in shares) at Jun. 30, 2018		189,053,214
Balance at Jun. 30, 2018	561,895	$ 1,939	1,723,865	13,063	(1,994)	(1,174,978)
Balance (in shares) at Mar. 31, 2018		187,972,218
Balance at Mar. 31, 2018	521,617	$ 1,929	1,621,479	16,076	(4,724)	(1,113,143)
Increase (Decrease) in Stockholders' Equity
Stock issued from exercise of stock options, net (in shares)		542,056
Stock issued from exercise of stock options, net	3,602	$ 5	3,597
Restricted stock tax vesting (in shares)		85,726
Restricted stock tax vesting	(115)		(115)
Stock-based compensation	6,341		6,341
Warrants exercised (in shares)		453,214
Warrants exercised	3,617	$ 5	6,625	(3,013)
Change in fair value of derivatives	85,938		85,938
Unrealized holding gain (loss) on available-for-sale securities	422				422
Foreign currency translation adjustment	2,308				2,308
Net loss	(61,833)					(61,833)
Balance (in shares) at Jun. 30, 2018		189,053,214
Balance at Jun. 30, 2018	$ 561,895	$ 1,939	1,723,865	13,063	(1,994)	(1,174,978)
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)		578,451
Stock issued from exercise of stock options, net	3,953	$ 6	3,947
Restricted stock tax vesting (in shares)		301,058
Restricted stock tax vesting	(1,940)		(1,940)
Stock issued for contingent consideration (in shares)		771,804
Stock issued for contingent consideration	9,316	$ 8	9,308
Stock-based compensation	12,744		12,744
Warrants exercised (in shares)		101,787
Warrants exercised	812	$ 1	1,487	(676)
Equity component of the convertible notes (in shares)		39,043,690
Equity component of the convertible notes	190,758	$ 390	190,368
Termination of capped call confirmations	14,632		14,632
Unrealized holding gain (loss) on available-for-sale securities	584				584
Foreign currency translation adjustment	(1,804)				(1,804)
Net loss	(120,299)					(120,299)
Balance (in shares) at Mar. 31, 2019		230,180,714
Balance at Mar. 31, 2019	$ 451,668	$ 2,347	1,970,607	12,387	(1,152)	(1,532,521)
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
Unrealized holding gain (loss) on available-for-sale securities	562
Foreign currency translation adjustment	77
Net loss	$ (204,850)
Balance (in shares) at Jun. 30, 2019	254,513,522	254,513,522
Balance at Jun. 30, 2019	$ 600,058	$ 2,589	2,201,447	12,387	707	(1,617,072)
Balance (in shares) at Mar. 31, 2019		230,180,714
Balance at Mar. 31, 2019	451,668	$ 2,347	1,970,607	12,387	(1,152)	(1,532,521)
Increase (Decrease) in Stockholders' Equity
Stock issued from exercise of stock options, net (in shares)		561,177
Stock issued from exercise of stock options, net	$ 2,807	$ 5	2,802
Stock issued from equity financing (in shares)	18,700,000	18,720,930
Stock issued from equity financing	$ 188,994	$ 187	188,807
Restricted stock tax vesting (in shares)		99,252
Restricted stock tax vesting	(615)		(615)
Stock-based compensation	9,935		9,935
Equity component of the convertible notes (in shares)		4,951,449
Equity component of the convertible notes	24,718	$ 50	24,668
Termination of capped call confirmations	5,243		5,243
Unrealized holding gain (loss) on available-for-sale securities	(22)				(22)
Foreign currency translation adjustment	1,881				1,881
Net loss	$ (84,551)					(84,551)
Balance (in shares) at Jun. 30, 2019	254,513,522	254,513,522
Balance at Jun. 30, 2019	$ 600,058	$ 2,589	$ 2,201,447	$ 12,387	$ 707	$ (1,617,072)

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Operating activities
Net loss	$ (204,850)	$ (111,751)
Adjustments to reconcile net loss to net cash used in operating activities:
Amortization of debt discount and deferred financing	2,104	5,273
Depreciation and amortization	2,145	1,942
Stock-based compensation	22,679	13,819
Loss on exchange of convertible debt	40,624	0
Change in fair value of derivatives	0	2,739
Non-cash changes in the fair value of contingent consideration payable	1,863	1,400
Foreign currency remeasurement loss	530	2,107
Changes in operating assets and liabilities:
Accounts receivable	(6,829)	(6,043)
Inventories	(1,908)	(3,449)
Prepaid expenses and other current assets	(3,523)	4,584
Accounts payable and accrued expenses	12,453	(11,801)
Other non-current assets and liabilities	(819)	(336)
Deferred reimbursements	(1,500)	(5,000)
Net cash used in operating activities	(137,031)	(106,516)
Investing activities
Sale and redemption of marketable securities	261,425	210,239
Purchases of marketable securities	(191,318)	(380,234)
Capital expenditures	(5,110)	(1,881)
Net cash provided by (used in) investing activities	64,997	(171,876)
Financing activities
Proceeds from issuance of common stock, net of issuance costs	188,994	294,584
Payment of finance leases	(98)
Payment of finance leases		(142)
Purchase of vested restricted stock units	(2,555)	(2,027)
Proceeds from termination of capped call confirmations	19,875	0
Proceeds from exercise of stock options	6,760	7,580
Proceeds of exercise of warrants	812	3,617
Net cash provided by financing activities	213,788	303,612
Effect of exchange rate changes on cash, cash equivalents, and restricted cash	(941)	(1,016)
Net increase in cash, cash equivalents, and restricted cash	140,813	24,204
Cash, cash equivalents, and restricted cash at beginning of period	82,375	51,237
Cash, cash equivalents, and restricted cash at end of period	223,188	75,441
Cash paid during the period for interest
Cash paid during the period for interest	9,302	3,774
Capital expenditures, unpaid	837	0
Capital expenditures funded by capital lease	0	81
Payment of contingent consideration in shares	$ 9,316	$ 0

Business	6 Months Ended
Business	Jun. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Business	Business Amicus Therapeutics, Inc. (the "Company") is a global patient-dedicated biotechnology company engaged in the discovery, development, and commercialization of a diverse set of novel treatments for patients living with rare metabolic diseases. With one 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."), and Japan, with additional approvals granted and applications pending in several other geographies. During the third quarter of 2018, the Company initiated the commercial launch of Galafold^® in the U.S. for the treatment of adult patients with a confirmed diagnosis of Fabry disease and an amenable genetic variant. 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. 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 a recently expanded collaboration with the University of Pennsylvania ("Penn"). The Company's pipeline includes gene therapy programs in rare, neurologic lysosomal disorders ("LDs") with programs in CLN6, CLN3, and CLN8 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 rare diseases, including Rett Syndrome, Angelman Syndrome, Myotonic Dystophy, and select other muscular dystrophies. 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 six months ended June 30, 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 common stock, par value $0.01 per share. The Company had an accumulated deficit of $1.6 billion as of June 30, 2019 and anticipates incurring losses through the fiscal year ending December 31, 2019 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 2021. 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

6 Months Ended

Jun. 30, 2019

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Basis of Presentation

The Company has prepared the accompanying unaudited consolidated financial statements in accordance with accounting principles generally accepted in the United States of America ("U.S. GAAP") for interim financial information and with the instructions to Form 10-Q and Article 10-01 of Regulation S-X. Accordingly, they do not include all of the information and disclosures required by U.S. GAAP for complete financial statements. In the opinion of management, the accompanying unaudited financial statements reflect all adjustments, which include only normal recurring adjustments, necessary to present fairly the Company's interim financial information.

The accompanying unaudited consolidated financial statements and related notes should be read in conjunction with the Company's financial statements and related notes as contained in the Company's Annual Report on Form 10-K for the fiscal year ended December 31, 2018. For a complete description of the Company's accounting policies, please refer to the Annual Report on Form 10-K for the fiscal year ended December 31, 2018.

Consolidation

The consolidated financial statements include the accounts of the Company and its subsidiaries. Intercompany accounts and transactions have been 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.

Reclassification

Certain prior year amounts have been reclassified for comparative purposes. The reclassifications did not affect results of operations, net assets, or cash flows.

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 Consolidated Balance Sheets. Unrealized holding gains and losses are reported within comprehensive income (loss) in the Consolidated 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 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 cash and cash equivalents or its 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 June 30, 2019 have arisen from product sales primarily in the E.U. and 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 June 30, 2019, the Company recorded an allowance for doubtful accounts of $0.2 million.

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.

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 revenue from the sale of Galafold^® is 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:



	Three Months Ended June 30,				Six Months Ended June 30,
(in thousands)	2019		2018		2019		2018
U.S.	$	12,181	$	—	$	21,249	$	—
Ex-U.S.	31,949		21,309		56,927		38,005
Total net product sales	$	44,130	$	21,309	$	78,176	$	38,005

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 goods sold 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. A portion of the inventory available-for-sale was expensed as research and development costs prior to regulatory approval and as such the cost of goods sold and related gross margins are not necessarily indicative of future cost of goods sold and gross margin.

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 9. Leases" and "—Note 2. Summary of Significant Accounting Policies, Recent Accounting Developments - Guidance Adopted in 2019."

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.

In August 2018, the Securities Exchange Commission ("SEC") issued Final Rule 33-10532, Disclosure Update and Simplification, which amends certain disclosure requirements that were redundant, duplicative, overlapping, or superseded by other SEC disclosure requirements. The amendments generally eliminated or otherwise reduced certain disclosure requirements of various SEC rules and regulations. However, in some cases, the amendments require additional information to be disclosed, including changes in stockholders' equity in interim periods. The rule was effective 30 days after its publication in the Federal Register. The rule was posted on October 4, 2018. On September 25, 2018, the SEC released guidance advising it will not object to a registrant adopting the requirement to include changes in stockholders' equity in the Form 10-Q for the first quarter beginning after the effective date of the rule. The Company adopted the guidance for the period ended March 31, 2019.

Recent Accounting Developments - Guidance Not Yet Adopted

ASU 2018-13— In August 2018, the FASB issued ASU 2018-13, 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 changes (i) 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. Early adoption is permitted. An entity is permitted to early adopt any removed or modified disclosures upon issuance of ASU 2018-13 and delay adoption of the additional disclosures until their effective date. The Company is currently assessing the impact that this standard will have on its consolidated financial statements upon adoption.

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. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The Company is currently assessing the impact that this standard will have on its consolidated financial statements upon adoption.

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 is currently assessing the impact that this standard will have on its consolidated financial statements upon adoption.

Cash, Cash Equivalents, Marketable Securities and Restricted Cash

6 Months Ended

Jun. 30, 2019

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

Cash, Cash Equivalents, Marketable Securities and Restricted Cash

Cash, Cash Equivalents, Marketable Securities, and Restricted Cash

As of June 30, 2019, the Company held $220.6 million in cash and cash equivalents and $355.1 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, while investments that have maturities greater than one year are classified as long-term.

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



	As of June 30, 2019
(in thousands)	Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Cash and cash equivalents	$	220,578	$	—	$	—		$	220,578
Corporate debt securities	169,425		148		(15		)	169,558
Commercial paper	111,872		156		(2		)	112,026
Asset-backed securities	73,025		68		—			73,093
Money market	350		—		—			350
Certificates of deposit	51		—		—			51
	$	575,301	$	372	$	(17	)	$	575,656
Included in cash and cash equivalents	$	220,578	$	—	$	—		$	220,578
Included in marketable securities	354,723		372		(17		)	355,078
Total cash, cash equivalents, and marketable securities	$	575,301	$	372	$	(17	)	$	575,656



	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 six months ended June 30, 2019 there were no realized gains. 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 June 30, 2019 and December 31, 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 $38.5 million and $403.1 million as of June 30, 2019 and December 31, 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)	June 30, 2019		December 31, 2018		June 30, 2018		December 31, 2017
Cash and cash equivalents	$	220,578	$	79,749	$	73,311	$	49,060
Restricted cash	2,610		2,626		2,130		2,177
Cash, cash equivalents, and restricted cash shown in the Consolidated Statements of Cash Flows	$	223,188	$	82,375	$	75,441	$	51,237

Inventories

6 Months Ended

Jun. 30, 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)	June 30, 2019		December 31, 2018
Raw materials	$	4,018	$	1,291
Work-in-process	3,320		3,485
Finished goods	3,057		3,614
Total inventories	$	10,395	$	8,390

The Company recorded a reserve for inventory of $0.2 million as of June 30, 2019 and December 31, 2018.

Debt

6 Months Ended

Jun. 30, 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 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 payable by the Company.

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 payable by the Company. In addition, the Company used $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 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 $6.12 per share of the Company's common stock, subject to adjustment under certain conditions.

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 through earnings on the Consolidated Statements of Operations resulting in a change in fair value of derivatives for the three and six months ended June 30, 2018 of $(7.6) million and $(2.7) million, respectively.

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.

During the six months ended June 30, 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 during the six months ended June 30, 2019, to the Holders to satisfy accrued and unpaid interest to the closing date of the transaction, along with cash in lieu of fractional shares. The transaction resulted in $215.0 million in additional paid-in-capital and common stock of $0.4 million in the Consolidated Balance Sheets as of June 30, 2019. Additionally, the Company recognized a net loss on the exchange of debt of $36.1 million and $4.5 million in the Consolidated Statements of Operations for the quarters ended March 31, 2019 and June 30, 2019, respectively.

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 second quarter. As a result, the remaining Convertible Notes are currently convertible into the Company's common stock.

During the six months ended June 30, 2019, the Company also terminated the Capped Call Confirmations related to the exchange of the Convertible Notes for proceeds of $19.9 million.

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



Liability component (in thousands)			June 30, 2019			December 31, 2018
Principal			$	152,825		$	400,000
Less: debt discount	⁽¹⁾		(3,373		)	(74,145		)
Less: deferred financing		⁽¹⁾	(388		)	(4,115		)
Net carrying value of the debt			$	149,064		$	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 total interest expense recognized related to the Convertible Notes and Senior Secured Term Loan for the three and six months ended June 30, 2019 and 2018, respectively:



	Three Months Ended June 30,				Six Months Ended June 30,
Interest component (in thousands)	2019		2018		2019		2018
Contractual interest expense	$	4,146	$	1,888	$	8,959	$	3,775
Amortization of debt discount	423		2,539		1,982		5,011
Amortization of deferred financing	39		133		122		262
Total	$	4,608	$	4,560	$	11,063	$	9,048

Stockholders' Equity	6 Months Ended
Stockholders' Equity	Jun. 30, 2019
Equity [Abstract]
Stockholders' Equity	Stockholders' Equity During the six months ended June 30, 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 5. Debt'' during the six months ended June 30, 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. As discussed in "— Note 8. 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.

Share-Based Compensation

6 Months Ended

Jun. 30, 2019

Share-based Payment Arrangement [Abstract]

Share-Based Compensation

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 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.

Stock Option Grants

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:



		Three Months Ended June 30,						Six Months Ended June 30,
		2019			2018			2019			2018
Expected stock price volatility		74.2		%	81.1		%	74.2		%	81.2		%
Risk free interest rate		2.0		%	2.8		%	2.4		%	2.4		%
Expected life of options (years)	⁽¹⁾	5.68			5.62			5.68			5.62
Expected annual dividend per share		$	—		$	—		$	—		$	—

______________________________________

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

A summary of the Company's stock options for the six months ended June 30, 2019 were as follows:



	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life	Aggregate Intrinsic Value
	(in thousands)					(in millions)
Options outstanding, December 31, 2018	15,810		$	8.63
Granted	3,683		$	10.36
Exercised	(1,139	)	$	5.93
Forfeited	(445	)	$	11.02
Expired	(60	)	$	13.61
Options outstanding, June 30, 2019	17,849		$	9.09	6.8 years	$	68.7
Vested and unvested expected to vest, June 30, 2019	16,975		$	8.99	6.7 years	$	66.8
Exercisable at June 30, 2019	10,624		$	8.14	5.5 years	$	50.1

As of June 30, 2019, the total unrecognized compensation cost related to non-vested stock options granted was $40.8 million and is expected to be recognized over a weighted average period of three years.

Restricted Stock Units and Performance-Based Restricted Stock Units (collectively "RSUs")

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 six months ended June 30, 2019 is as follows:



	Number of Shares		Weighted Average Grant Date Fair Value		Weighted Average Remaining Years	Aggregate Intrinsic Value
	(in thousands)					(in millions)
Non-vested units as of December 31, 2018	3,712		$	10.59
Granted	3,262		$	11.02
Vested	(788	)	$	9.28
Forfeited	(301	)	$	10.32
Non-vested units as of June 30, 2019	5,885		$	11.09	2.7 years	$	73.5

All non-vested units granted as of June 30, 2019 are expected to vest over their normal term. As of June 30, 2019, there was $47.5 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 three 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:



	Three Months Ended June 30,				Six Months Ended June 30,
(in thousands)	2019		2018		2019		2018
Equity compensation expense recognized in:
Research and development expense	$	3,952	$	2,641	$	8,984	$	5,698
Selling, general, and administrative expense	5,983		3,700		13,695		8,121
Total equity compensation expense	$	9,935	$	6,341	$	22,679	$	13,819

Assets and Liabilities Measured at Fair Value

6 Months Ended

Jun. 30, 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 June 30, 2019 are identified in the following table:



(in thousands)	Level 2		Total
Assets:
Commercial paper	$	112,026	$	112,026
Asset-backed securities	73,093		73,093
Corporate debt securities	169,558		169,558
Money market funds	4,224		4,224
	$	358,901	$	358,901



	Level 2		Level 3		Total
Liabilities:
Contingent consideration payable	$	—	$	21,247	$	21,247
Deferred compensation plan liability	3,874		—		3,874
	$	3,874	$	21,247	$	25,121

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, 2018 are identified in the following table:



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



	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 fall 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 debt at June 30, 2019 was $6.1 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 June 30, 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 debt securities 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 six months ended June 30, 2019. No transfers of assets between Level 1 and Level 2 of the fair value measurement hierarchy occurred during the six months ended June 30, 2019.

Contingent Consideration Payable

The contingent consideration payable resulted from the acquisition of Callidus Biopharma, Inc. ("Callidus") in November 2013. 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 ATB200 Pompe program:



Contingent Consideration Liability	Fair Value as of June 30, 2019	Valuation Technique	Unobservable Input	Range
	(in thousands)

			Discount rate	10.1%

Clinical and regulatory milestones	$20,999	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 three and six months ended June 30, 2019 and 2018, respectively:



	Three Months Ended June 30,				Six Months Ended June 30,
(in thousands)	2019		2018		2019			2018
Balance, beginning of the period	$	20,767	$	26,500	$	28,700		$	25,400
Payment of contingent consideration in stock	—		—		(9,316		)	—
Changes in fair value during the period, included in the Consolidated Statements of Operations	480		300		1,863			1,400
Balance, end of the period	$	21,247	$	26,800	$	21,247		$	26,800

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

Leases

6 Months Ended

Jun. 30, 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 three and six months ended June 30, 2019, operating lease expense was $2.7 million and $4.8 million, respectively. For the six months ended June 30, 2019, the Company paid $2.4 million for amounts included in the measurement of operating lease liabilities and recorded $0.2 million of right-of-use assets obtained 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)	June 30, 2019
Operating lease ROU asset	$	35,052

Current portion of the operating lease liabilities	$	2,678
Non-current portion of the operating lease liabilities	36,259
Total operating lease liability	$	38,937

Weighted-average remaining lease terms (years)	14.8
Weighted-average discount rate	12.9		%

At June 30, 2019, the future minimum lease payments were as follows:



( in thousands)	Operating Leases
2019 (excludes the six months ended June 30, 2019)	$	2,781
2020	9,647
2021	10,566
2022	10,411
2023	10,789
Thereafter	174,673
Total lease payments	$	218,867
Less lease incentives	(28,939		)
Less imputed interest	(150,991		)
Total operating lease liability	$	38,937

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



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

Leases

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)	June 30, 2019
Operating lease ROU asset	$	35,052

Current portion of the operating lease liabilities	$	2,678
Non-current portion of the operating lease liabilities	36,259
Total operating lease liability	$	38,937

Weighted-average remaining lease terms (years)	14.8
Weighted-average discount rate	12.9		%

At June 30, 2019, the future minimum lease payments were as follows:



( in thousands)	Operating Leases
2019 (excludes the six months ended June 30, 2019)	$	2,781
2020	9,647
2021	10,566
2022	10,411
2023	10,789
Thereafter	174,673
Total lease payments	$	218,867
Less lease incentives	(28,939		)
Less imputed interest	(150,991		)
Total operating lease liability	$	38,937

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



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

Basic and Diluted Net Loss per Common Share

6 Months Ended

Jun. 30, 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:



	Three Months Ended June 30,						Six Months Ended June 30,
(in thousands, except per share amounts)	2019			2018			2019			2018
Numerator:
Net loss attributable to common stockholders	$	(84,551	)	$	(61,833	)	$	(204,850	)	$	(111,751	)
Denominator:
Weighted average common shares outstanding — basic and diluted	238,089,824			188,621,423			225,848,013			182,303,128

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.

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:



	As of June 30,
(in thousands)	2019	2018
Options to purchase common stock	17,849	15,869
Convertible notes	462	40,850
Outstanding warrants, convertible to common stock	2,555	2,657
Unvested restricted stock units	5,885	3,556
Vested restricted stock units, unissued	227	111
Total number of potentially issuable shares	26,978	63,043

Summary of Significant Accounting Policies (Policies)	6 Months Ended
Summary of Significant Accounting Policies (Policies)	Jun. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The Company has prepared the accompanying unaudited consolidated financial statements in accordance with accounting principles generally accepted in the United States of America ("U.S. GAAP") for interim financial information and with the instructions to Form 10-Q and Article 10-01 of Regulation S-X. Accordingly, they do not include all of the information and disclosures required by U.S. GAAP for complete financial statements. In the opinion of management, the accompanying unaudited financial statements reflect all adjustments, which include only normal recurring adjustments, necessary to present fairly the Company's interim financial information. The accompanying unaudited consolidated financial statements and related notes should be read in conjunction with the Company's financial statements and related notes as contained in the Company's Annual Report on Form 10-K for the fiscal year ended December 31, 2018. For a complete description of the Company's accounting policies, please refer to the Annual Report on Form 10-K for the fiscal year ended December 31, 2018.
Consolidation	Consolidation The consolidated financial statements include the accounts of the Company and its subsidiaries. Intercompany accounts and transactions have been 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.
Reclassification	Reclassification Certain prior year amounts have been reclassified for comparative purposes. The reclassifications did not affect results of operations, net assets, or cash flows.
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 Consolidated Balance Sheets. Unrealized holding gains and losses are reported within comprehensive income (loss) in the Consolidated 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 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 cash and cash equivalents or its 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 June 30, 2019 have arisen from product sales primarily in the E.U. and 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.
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. 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 revenue from the sale of Galafold^® is 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 goods sold 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. A portion of the inventory available-for-sale was expensed as research and development costs prior to regulatory approval and as such the cost of goods sold and related gross margins are not necessarily indicative of future cost of goods sold and gross margin.
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 9. Leases" and "—Note 2. Summary of Significant Accounting Policies, Recent Accounting Developments - Guidance Adopted in 2019."
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. In August 2018, the Securities Exchange Commission ("SEC") issued Final Rule 33-10532, Disclosure Update and Simplification, which amends certain disclosure requirements that were redundant, duplicative, overlapping, or superseded by other SEC disclosure requirements. The amendments generally eliminated or otherwise reduced certain disclosure requirements of various SEC rules and regulations. However, in some cases, the amendments require additional information to be disclosed, including changes in stockholders' equity in interim periods. The rule was effective 30 days after its publication in the Federal Register. The rule was posted on October 4, 2018. On September 25, 2018, the SEC released guidance advising it will not object to a registrant adopting the requirement to include changes in stockholders' equity in the Form 10-Q for the first quarter beginning after the effective date of the rule. The Company adopted the guidance for the period ended March 31, 2019. Recent Accounting Developments - Guidance Not Yet Adopted ASU 2018-13— In August 2018, the FASB issued ASU 2018-13, 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 changes (i) 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. Early adoption is permitted. An entity is permitted to early adopt any removed or modified disclosures upon issuance of ASU 2018-13 and delay adoption of the additional disclosures until their effective date. The Company is currently assessing the impact that this standard will have on its consolidated financial statements upon adoption. 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. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The Company is currently assessing the impact that this standard will have on its consolidated financial statements upon adoption. 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 is currently assessing the impact that this standard will have on its consolidated financial statements upon adoption.

Summary of Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2019

Accounting Policies [Abstract]

Disaggregation of Revenue

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



	Three Months Ended June 30,				Six Months Ended June 30,
(in thousands)	2019		2018		2019		2018
U.S.	$	12,181	$	—	$	21,249	$	—
Ex-U.S.	31,949		21,309		56,927		38,005
Total net product sales	$	44,130	$	21,309	$	78,176	$	38,005

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

6 Months Ended

Jun. 30, 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 June 30, 2019
(in thousands)	Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Cash and cash equivalents	$	220,578	$	—	$	—		$	220,578
Corporate debt securities	169,425		148		(15		)	169,558
Commercial paper	111,872		156		(2		)	112,026
Asset-backed securities	73,025		68		—			73,093
Money market	350		—		—			350
Certificates of deposit	51		—		—			51
	$	575,301	$	372	$	(17	)	$	575,656
Included in cash and cash equivalents	$	220,578	$	—	$	—		$	220,578
Included in marketable securities	354,723		372		(17		)	355,078
Total cash, cash equivalents, and marketable securities	$	575,301	$	372	$	(17	)	$	575,656



	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 restricted cash and cash equivalents



(in thousands)	June 30, 2019		December 31, 2018		June 30, 2018		December 31, 2017
Cash and cash equivalents	$	220,578	$	79,749	$	73,311	$	49,060
Restricted cash	2,610		2,626		2,130		2,177
Cash, cash equivalents, and restricted cash shown in the Consolidated Statements of Cash Flows	$	223,188	$	82,375	$	75,441	$	51,237

Inventories (Tables)

6 Months Ended

Jun. 30, 2019

Inventory Disclosure [Abstract]

Schedule of inventories for the period

The following table summarizes the components of inventories:



(in thousands)	June 30, 2019		December 31, 2018
Raw materials	$	4,018	$	1,291
Work-in-process	3,320		3,485
Finished goods	3,057		3,614
Total inventories	$	10,395	$	8,390

Debt (Tables)

6 Months Ended

Jun. 30, 2019

Debt Disclosure [Abstract]

Schedule of liability components of the Convertible Notes

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



Liability component (in thousands)			June 30, 2019			December 31, 2018
Principal			$	152,825		$	400,000
Less: debt discount	⁽¹⁾		(3,373		)	(74,145		)
Less: deferred financing		⁽¹⁾	(388		)	(4,115		)
Net carrying value of the debt			$	149,064		$	321,740

______________________________________

Components of total interest expense recognized related to the Convertible Notes

The following table sets forth total interest expense recognized related to the Convertible Notes and Senior Secured Term Loan for the three and six months ended June 30, 2019 and 2018, respectively:



	Three Months Ended June 30,				Six Months Ended June 30,
Interest component (in thousands)	2019		2018		2019		2018
Contractual interest expense	$	4,146	$	1,888	$	8,959	$	3,775
Amortization of debt discount	423		2,539		1,982		5,011
Amortization of deferred financing	39		133		122		262
Total	$	4,608	$	4,560	$	11,063	$	9,048

Share-Based Compensation (Tables)

6 Months Ended

Jun. 30, 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:



		Three Months Ended June 30,						Six Months Ended June 30,
		2019			2018			2019			2018
Expected stock price volatility		74.2		%	81.1		%	74.2		%	81.2		%
Risk free interest rate		2.0		%	2.8		%	2.4		%	2.4		%
Expected life of options (years)	⁽¹⁾	5.68			5.62			5.68			5.62
Expected annual dividend per share		$	—		$	—		$	—		$	—

______________________________________

⁽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 six months ended June 30, 2019 were as follows:



	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life	Aggregate Intrinsic Value
	(in thousands)					(in millions)
Options outstanding, December 31, 2018	15,810		$	8.63
Granted	3,683		$	10.36
Exercised	(1,139	)	$	5.93
Forfeited	(445	)	$	11.02
Expired	(60	)	$	13.61
Options outstanding, June 30, 2019	17,849		$	9.09	6.8 years	$	68.7
Vested and unvested expected to vest, June 30, 2019	16,975		$	8.99	6.7 years	$	66.8
Exercisable at June 30, 2019	10,624		$	8.14	5.5 years	$	50.1

Schedule of Non-Vested RSU Activity under the Plan

A summary of non-vested RSU activity under the Plan for the six months ended June 30, 2019 is as follows:



	Number of Shares		Weighted Average Grant Date Fair Value		Weighted Average Remaining Years	Aggregate Intrinsic Value
	(in thousands)					(in millions)
Non-vested units as of December 31, 2018	3,712		$	10.59
Granted	3,262		$	11.02
Vested	(788	)	$	9.28
Forfeited	(301	)	$	10.32
Non-vested units as of June 30, 2019	5,885		$	11.09	2.7 years	$	73.5

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:



	Three Months Ended June 30,				Six Months Ended June 30,
(in thousands)	2019		2018		2019		2018
Equity compensation expense recognized in:
Research and development expense	$	3,952	$	2,641	$	8,984	$	5,698
Selling, general, and administrative expense	5,983		3,700		13,695		8,121
Total equity compensation expense	$	9,935	$	6,341	$	22,679	$	13,819

Assets and Liabilities Measured at Fair Value (Tables)

6 Months Ended

Jun. 30, 2019

Fair Value Disclosures [Abstract]

Summary of assets and liabilities subject to fair value measurements



(in thousands)	Level 2		Total
Assets:
Commercial paper	$	112,026	$	112,026
Asset-backed securities	73,093		73,093
Corporate debt securities	169,558		169,558
Money market funds	4,224		4,224
	$	358,901	$	358,901



	Level 2		Level 3		Total
Liabilities:
Contingent consideration payable	$	—	$	21,247	$	21,247
Deferred compensation plan liability	3,874		—		3,874
	$	3,874	$	21,247	$	25,121



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



	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

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Schedule of changes in contingent consideration payable

The following table shows the change in the balance of contingent consideration payable for the three and six months ended June 30, 2019 and 2018, respectively:



	Three Months Ended June 30,				Six Months Ended June 30,
(in thousands)	2019		2018		2019			2018
Balance, beginning of the period	$	20,767	$	26,500	$	28,700		$	25,400
Payment of contingent consideration in stock	—		—		(9,316		)	—
Changes in fair value during the period, included in the Consolidated Statements of Operations	480		300		1,863			1,400
Balance, end of the period	$	21,247	$	26,800	$	21,247		$	26,800

Callidus Biopharma Inc

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

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 ATB200 Pompe program:



Contingent Consideration Liability	Fair Value as of June 30, 2019	Valuation Technique	Unobservable Input	Range
	(in thousands)

			Discount rate	10.1%

Clinical and regulatory milestones	$20,999	Probability weighted discounted cash flow	Probability of achievement of milestones	75%-78%

			Projected year of payments	2021-2022

- 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

Leases (Tables)

6 Months Ended

Jun. 30, 2019

Leases [Abstract]

Lease costs

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



(in thousands, except year and discount rate amounts)	June 30, 2019
Operating lease ROU asset	$	35,052

Current portion of the operating lease liabilities	$	2,678
Non-current portion of the operating lease liabilities	36,259
Total operating lease liability	$	38,937

Weighted-average remaining lease terms (years)	14.8
Weighted-average discount rate	12.9		%

Future minimum lease payments, operating leases

At June 30, 2019, the future minimum lease payments were as follows:



( in thousands)	Operating Leases
2019 (excludes the six months ended June 30, 2019)	$	2,781
2020	9,647
2021	10,566
2022	10,411
2023	10,789
Thereafter	174,673
Total lease payments	$	218,867
Less lease incentives	(28,939		)
Less imputed interest	(150,991		)
Total operating lease liability	$	38,937

Schedule of future minimum lease payments

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



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

Basic and Diluted Net Loss per Common Share (Tables)

6 Months Ended

Jun. 30, 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:



	Three Months Ended June 30,						Six Months Ended June 30,
(in thousands, except per share amounts)	2019			2018			2019			2018
Numerator:
Net loss attributable to common stockholders	$	(84,551	)	$	(61,833	)	$	(204,850	)	$	(111,751	)
Denominator:
Weighted average common shares outstanding — basic and diluted	238,089,824			188,621,423			225,848,013			182,303,128

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:



	As of June 30,
(in thousands)	2019	2018
Options to purchase common stock	17,849	15,869
Convertible notes	462	40,850
Outstanding warrants, convertible to common stock	2,555	2,657
Unvested restricted stock units	5,885	3,556
Vested restricted stock units, unissued	227	111
Total number of potentially issuable shares	26,978	63,043

Business (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Class of Stock [Line Items]
Common stock issued from underwriting agreement (in shares)	18.7
Proceeds from issuance of common stock, net of issuance costs	$ 189,000	$ 188,994	$ 294,584
Exchange agreement, aggregate principal amount	$ 247,200	$ 247,200
Shares authorized for issuance (in shares)	44.0	44.0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01		$ 0.01
Accumulated deficit	$ (1,617,072)	$ (1,617,072)		$ (1,412,222)
Underwritten Offering
Class of Stock [Line Items]
Stock issued (in dollars per share)	$ 10.75	$ 10.75

Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for doubtful accounts receivable	$ 200		$ 200
Net product sales	44,130	$ 21,309	78,176	$ 38,005
Operating lease, liability	38,937		38,937
Operating lease ROU asset	35,052		35,052
ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, liability					$ 17,600
Operating lease ROU asset	17,600		17,600
U.S.
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net product sales	12,181	0	21,249	0
Ex-U.S.
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net product sales	$ 31,949	$ 21,309	$ 56,927	$ 38,005

Cash, Cash Equivalents, Marketable Securities and Restricted Cash - Components (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Cash, Money Market Funds, and Marketable Securities
Cash and cash equivalents	$ 220,578	$ 79,749	$ 73,311	$ 49,060
Fair value, Available-for-sale debt securities	355,078	424,403
Fair Value, Cash balances	220,578	79,749
Cost, available-for-sale securities	354,723	424,830
Gross unrealized gain, available-for-sale securities	372	11
Gross unrealized loss, available-for-sale securities	(17)	(438)
Cost, Cash balances and available-for-sale securities	575,301	504,579
Gross unrealized gain, Cash balances and available-for-sale securities	372	11
Gross unrealized loss, Cash balances and available-for-sale securities	(17)	(438)
Fair value, Cash balances and available-for-sale securities	575,656	504,152
Corporate debt securities
Cash, Money Market Funds, and Marketable Securities
Fair value, Available-for-sale debt securities	169,558	240,726
Cost, available-for-sale securities	169,425	240,969
Gross unrealized gain, available-for-sale securities	148	7
Gross unrealized loss, available-for-sale securities	(15)	(250)
Commercial paper
Cash, Money Market Funds, and Marketable Securities
Fair value, Available-for-sale debt securities	112,026	115,141
Cost, available-for-sale securities	111,872	115,245
Gross unrealized gain, available-for-sale securities	156	0
Gross unrealized loss, available-for-sale securities	(2)	(104)
Asset-backed securities
Cash, Money Market Funds, and Marketable Securities
Fair value, Available-for-sale debt securities	73,093	68,135
Cost, available-for-sale securities	73,025	68,215
Gross unrealized gain, available-for-sale securities	68	4
Gross unrealized loss, available-for-sale securities	0	(84)
Money market
Cash, Money Market Funds, and Marketable Securities
Fair value, Available-for-sale debt securities	350	350
Cost, available-for-sale securities	350	350
Gross unrealized gain, available-for-sale securities	0	0
Gross unrealized loss, available-for-sale securities	0	0
Certificates of deposit
Cash, Money Market Funds, and Marketable Securities
Fair value, Available-for-sale debt securities	51	51
Cost, available-for-sale securities	51	51
Gross unrealized gain, available-for-sale securities	0	0
Gross unrealized loss, available-for-sale securities	$ 0	$ 0

Cash, Cash Equivalents, Marketable Securities and Restricted Cash - Additional Information (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Realized gain (loss) on debt securities	$ 0	$ 0
Fair value of available-for-sale debt securities in unrealized loss positions	38,500,000	403,100,000
Cash and cash equivalents	220,578,000	79,749,000	$ 73,311,000	$ 49,060,000
Restricted cash	2,610,000	2,626,000	2,130,000	2,177,000
Cash, cash equivalents, and restricted cash shown in the Consolidated Statements of Cash Flows	$ 223,188,000	$ 82,375,000	$ 75,441,000	$ 51,237,000

Inventories (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Inventory Disclosure [Abstract]
Raw materials	$ 4,018	$ 1,291
Work-in-process	3,320	3,485
Finished goods	3,057	3,614
Total inventories	10,395	8,390
Reserve for inventory	$ 200	$ 200

Debt (Details)			1 Months Ended		3 Months Ended			6 Months Ended
Debt (Details)	Feb. 16, 2018 shares	Feb. 15, 2018 USD ($) shares	Sep. 30, 2018 USD ($)	Dec. 31, 2016 USD ($) day $ / shares shares	Jun. 30, 2019 USD ($) $ / shares shares	Mar. 31, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) $ / shares shares	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) $ / shares shares	Jun. 07, 2018 USD ($) shares
Convertible Debt
Common stock issued from underwriting agreement (in shares) \| shares					18,700,000
Derivative liability, noncurrent		$ 507,400,000
Change in fair value of derivatives							$ (7,600,000)		$ (2,700,000)
Common stock, shares authorized (in shares) \| shares					500,000,000			500,000,000		500,000,000	500,000,000
Derivative liabilities											$ 88,300,000
Other assets, current											$ 2,400,000
Exchange agreement, aggregate principal amount					$ 247,200,000			$ 247,200,000
Shares authorized for issuance (in shares) \| shares					44,000,000.0			44,000,000.0
Common stock, par value (in dollars per share) \| $ / shares					$ 0.01			$ 0.01		$ 0.01
Exchange agreement, accrued and unpaid interest								$ 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
Gain (loss) on exchange of convertible debt					(4,501,000)	$ (36,100,000)	0	(40,624,000)	0
Proceeds from capped call confirmations, exchange of convertible debt								$ 19,875,000	0
Common Stock Capped Call Confirmation
Convertible Debt
Derivative asset, noncurrent		$ 13,600,000
Common Stock
Convertible Debt
Common stock issued from underwriting agreement (in shares) \| shares	885,000	19,400,000
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
Convertible Debt
Threshold percentage								130.00%
Convertible Notes \| Convertible Senior Notes 2016, Due 2023
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 trading days				20 days
Threshold consecutive trading days \| day				30
Debt Instruments [Abstract]
Principal					152,825,000			$ 152,825,000		$ 400,000,000
Less: debt discount					(3,373,000)			(3,373,000)		(74,145,000)
Less: deferred financing					(388,000)			(388,000)		(4,115,000)
Net carrying value of the debt					(149,064,000)			(149,064,000)		$ (321,740,000)
Interest expense
Contractual interest expense					4,146,000		1,888,000	8,959,000	3,775,000
Amortization of debt discount					423,000		2,539,000	1,982,000	5,011,000
Amortization of deferred financing					39,000		133,000	122,000	262,000
Total					$ 4,608,000		$ 4,560,000	$ 11,063,000	$ 9,048,000
Convertible Notes \| Convertible Senior Notes 2016, Due 2023 \| 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%

Stockholders' Equity - Common Stock and Warrants (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended			6 Months Ended
	Feb. 16, 2018	Feb. 15, 2018	Jun. 30, 2019	Mar. 31, 2019	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Collaborative Agreements
Common stock issued from underwriting agreement (in shares)			18,700,000
Proceeds of exercise of warrants						$ 812	$ 3,617
Proceeds from issuance of common stock, net of issuance costs			$ 189,000			188,994	$ 294,584
Exchange agreement, aggregate principal amount			$ 247,200			$ 247,200
Shares authorized for issuance (in shares)			44,000,000.0			44,000,000.0
Common stock, par value (in dollars per share)			$ 0.01			$ 0.01		$ 0.01
Contingent consideration, milestone payment				$ 9,000
Milestone payment, stock issued as consideration						$ 9,000
Common Stock
Collaborative Agreements
Common stock issued from underwriting agreement (in shares)			18,720,930		20,239,839
Milestone payment, stock issued as consideration				$ 9,300
Underwritten Offering
Collaborative Agreements
Stock issued (in dollars per share)			$ 10.75			$ 10.75
Common Stock
Collaborative Agreements
Common stock issued from underwriting agreement (in shares)	885,000	19,400,000
Outstanding warrants, convertible to common stock
Collaborative Agreements
Common stock issued from underwriting agreement (in shares)						101,787
Proceeds of exercise of warrants						$ 800
Outstanding warrants, convertible to common stock \| Common Stock
Collaborative Agreements
Warrants exercise price (in dollars per share)			$ 7.98			$ 7.98

Share-Based Compensation - Weighted-average Assumptions (Details) - Options to purchase common stock - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected stock price volatility	74.20%	81.10%	74.20%	81.20%
Risk free interest rate	2.00%	2.80%	2.40%	2.40%
Expected life of options (years)	5 years 8 months 4 days	5 years 7 months 13 days	5 years 8 months 4 days	5 years 7 months 13 days
Expected annual dividend per share (in dollars per share)	$ 0	$ 0	$ 0	$ 0

Share-Based Compensation - Stock Option Activity (Details) - Options to purchase common stock - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	6 Months Ended
	Jun. 30, 2019
Number of Shares
Options outstanding (in shares)	15,810
Options, Granted (in shares)	3,683
Options, Exercised (in shares)	(1,139)
Options, Forfeited (in shares)	(445)
Options, Expired (in shares)	(60)
Options outstanding (in shares)	17,849
Options, Vested and unvested expected to vest (in shares)	16,975
Options, Exercisable (in shares)	10,624
Weighted Average Exercise Price
Option outstanding (in dollars per share)	$ 8.63
Options, Granted (in dollars per share)	10.36
Options, Exercised (in dollars per share)	5.93
Options, Forfeited (in dollars per share)	11.02
Options, Expired (in dollars per share)	13.61
Option outstanding (in dollars per share)	9.09
Options, Vested and unvested expected to vest (in dollars per share)	8.99
Options, Exercisable (in dollars per share)	$ 8.14
Additional Disclosures
Weighted average remaining contractual life, options outstanding	6 years 9 months 18 days
Weighted average remaining contractual life, options vested and unvested expected to vest	6 years 8 months 12 days
Weighted average remaining contractual life, options exercisable	5 years 6 months
Aggregate intrinsic value, options outstanding	$ 68.7
Aggregate intrinsic value, vested and unvested expected to vest	66.8
Aggregate intrinsic value, exercisable	$ 50.1

Share-Based Compensation - Narrative (Details) shares in Thousands, $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($) shares
Options to purchase common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation costs	$ 40.8
Unrecognized compensation costs, period for recognition (in years)	3 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]
Total unrecognized compensation costs	$ 47.5
Unrecognized compensation costs, period for recognition (in years)	3 years
RSUs vested and non-vested units expected to vest (in shares) \| shares	788

Share-Based Compensation - RSUs and PBRSUs Summary (Details) - Unvested restricted stock units - Stock Option Plan Amended Restated 2007 Equity Incentive Plan $ / shares in Units, shares in Thousands, $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($) $ / shares shares
Number of Shares
Non-vested units (in shares) \| shares	3,712
Granted (in shares) \| shares	3,262
Vested (in shares) \| shares	(788)
Forfeited (in shares) \| shares	(301)
Non-vested units (in shares) \| shares	5,885
Weighted Average Grant Date Fair Value
Non-vested units (in dollars per share) \| $ / shares	$ 10.59
Granted (in dollars per share) \| $ / shares	11.02
Vested (in dollars per share) \| $ / shares	9.28
Forfeited (in dollars per share) \| $ / shares	10.32
Non-vested units (in dollars per share) \| $ / shares	$ 11.09
Additional Disclosures
Non-vested units, weighted average remaining years	2 years 8 months 12 days
Non-vested units, aggregate intrinsic value \| $	$ 73.5

Share-Based Compensation - Expense Summary (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total equity compensation expense	$ 9,935	$ 6,341	$ 22,679	$ 13,819
Research and development expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total equity compensation expense	3,952	2,641	8,984	5,698
Selling, general, and administrative expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total equity compensation expense	$ 5,983	$ 3,700	$ 13,695	$ 8,121

Assets and Liabilities Measured at Fair Value - Components by Hierarchy Level (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Mar. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Assets:
Fair value of assets		$ 358,901	$ 427,084
Liabilities:
Contingent consideration payable		21,247	19,700
Deferred compensation plan liability		3,874	2,732
Fair value of liabilities		25,121	22,432
Exchange agreement, aggregate principal amount		247,200
Milestone payment, stock issued as consideration		9,000
Common Stock
Liabilities:
Milestone payment, stock issued as consideration	$ 9,300
ATB200 Pompe Program \| Contingent Consideration Liability Clinical and Regulatory Milestones \| Callidus Biopharma Inc
Liabilities:
Contingent consideration payable		$ 20,999
ATB200 Pompe Program \| Contingent Consideration Liability Clinical and Regulatory Milestones \| Probability of Milestone Achievement \| Minimum \| Callidus Biopharma Inc
Liabilities:
Discount rate		0.75
ATB200 Pompe Program \| Contingent Consideration Liability Clinical and Regulatory Milestones \| Probability of Milestone Achievement \| Maximum \| Callidus Biopharma Inc
Liabilities:
Discount rate		0.78
Commercial paper
Assets:
Fair value of assets		$ 112,026	115,141
Asset-backed securities
Assets:
Fair value of assets		73,093	68,135
Corporate debt securities
Assets:
Fair value of assets		169,558	240,726
Money market funds
Assets:
Fair value of assets		4,224	3,082
Level 2
Assets:
Fair value of assets		358,901	427,084
Liabilities:
Contingent consideration payable		0	0
Deferred compensation plan liability		3,874	2,732
Fair value of liabilities		3,874	2,732
Convertible debt, fair value		6,100
Level 2 \| Commercial paper
Assets:
Fair value of assets		112,026	115,141
Level 2 \| Asset-backed securities
Assets:
Fair value of assets		73,093	68,135
Level 2 \| Corporate debt securities
Assets:
Fair value of assets		169,558	240,726
Level 2 \| Money market funds
Assets:
Fair value of assets		4,224	3,082
Level 3
Liabilities:
Contingent consideration payable		21,247	19,700
Deferred compensation plan liability		0	0
Fair value of liabilities		$ 21,247	$ 19,700
Level 3 \| ATB200 Pompe Program \| Contingent Consideration Liability Clinical and Regulatory Milestones \| Probability Weighted Discounted Cash Flow \| Discount Rate \| Callidus Biopharma Inc
Liabilities:
Discount rate		0.101

Assets and Liabilities Measured at Fair Value - Level 3 Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of the period	$ 20,767	$ 26,500	$ 28,700	$ 25,400
Payment of contingent consideration in stock	0	0	(9,316)	0
Changes in fair value during the period, included in the Consolidated Statements of Operations	480	300	1,863	1,400
Balance, end of the period	$ 21,247	$ 26,800	$ 21,247	$ 26,800

Leases (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Leases (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Leases [Abstract]
Operating lease cost	$ 2,700	$ 4,800
Cash paid for amounts included in operating lease liabilities		2,400
Right-of-use assets obtained in exchange for new operating lease liabilities		200
Operating lease ROU asset	35,052	35,052
Current portion of the operating lease liabilities	2,678	2,678
Non-current portion of the operating lease liabilities	36,259	36,259
Total operating lease liability	$ 38,937	$ 38,937
Weighted-average remaining lease terms (years)	14 years 9 months 18 days	14 years 9 months 18 days
Weighted-average discount rate	12.90%	12.90%
Operating Leases
2019 (excludes the six months ended June 30, 2019)	$ 2,781	$ 2,781
2020	9,647	9,647
2021	10,566	10,566
2022	10,411	10,411
2023	10,789	10,789
Thereafter	174,673	174,673
Total	218,867	218,867
Less lease incentives	(28,939)	(28,939)
Less imputed interest	$ (150,991)	$ (150,991)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2019			$ 6,244
2020			4,063
2021			3,560
2022			3,371
2023			3,611
Thereafter			10,038
Total lease payments			$ 30,887

Basic and Diluted Net Loss per Common Share (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator:
Net loss attributable to common stockholders	$ (84,551)	$ (120,299)	$ (61,833)	$ (49,916)	$ (204,850)	$ (111,751)
Denominator:
Weighted-average common shares outstanding - basic and diluted (in shares)	238,089,824		188,621,423		225,848,013	182,303,128
Antidilutive securities excluded from computation of diluted earnings per share (in shares)					26,978,000	63,043,000
Options to purchase common stock
Denominator:
Antidilutive securities excluded from computation of diluted earnings per share (in shares)					17,849,000	15,869,000
Convertible notes
Denominator:
Antidilutive securities excluded from computation of diluted earnings per share (in shares)					462,000	40,850,000
Outstanding warrants, convertible to common stock
Denominator:
Antidilutive securities excluded from computation of diluted earnings per share (in shares)					2,555,000	2,657,000
Unvested restricted stock units
Denominator:
Antidilutive securities excluded from computation of diluted earnings per share (in shares)					5,885,000	3,556,000
Vested restricted stock units, unissued
Denominator:
Antidilutive securities excluded from computation of diluted earnings per share (in shares)					227,000	111,000

Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2019	Jul. 30, 2019
Cover page.
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 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 each class	Common Stock
Trading Symbol	FOLD
Security Exchange Name	NASDAQ
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 Common Stock, Shares Outstanding		254,626,063
Entity Central Index Key	0001178879
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Amendment Flag	false

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 220,578	$ 79,749
Investments in marketable securities	355,078	424,403
Accounts receivable	28,709	21,962
Inventories	10,395	8,390
Prepaid expenses and other current assets	20,116	16,592
Total current assets	634,876	551,096
Operating lease right-of-use assets, less accumulated amortization of $2,641 and $0 at June 30, 2019 and December 31, 2018, respectively	35,052
Property and equipment, less accumulated depreciation of $16,890 and $15,671 at June 30, 2019 and December 31, 2018, respectively	15,273	11,375
In-process research & development	23,000	23,000
Goodwill	197,797	197,797
Other non-current assets	12,035	6,683
Total Assets	918,033	789,951
Current liabilities:
Accounts payable, accrued expenses, and other current liabilities	84,119	80,625
Deferred reimbursements	2,750	5,500
Operating lease liabilities	2,678
Total current liabilities	89,547	86,125
Deferred reimbursements	11,406	10,156
Convertible notes	2,070	175,006
Senior secured term loan	146,994	146,734
Contingent consideration payable	21,247	19,700
Deferred income taxes	6,465	6,465
Operating lease liabilities	36,259
Other non-current liabilities	3,987	2,853
Total liabilities	317,975	447,039
Commitments and contingencies
Stockholders’ equity:
Common stock, $0.01 par value, 500,000,000 shares authorized, 254,513,522 and 189,383,924 shares issued and outstanding at June 30, 2019 and December 31, 2018, respectively	2,589	1,942
Additional paid-in capital	2,201,447	1,740,061
Accumulated other comprehensive loss:
Foreign currency translation adjustment	352	495
Unrealized gain on available-for-sale securities	355	(427)
Warrants	12,387	13,063
Accumulated deficit	(1,617,072)	(1,412,222)
Total stockholders’ equity	600,058	342,912
Total Liabilities and Stockholders’ Equity	$ 918,033	$ 789,951

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Less accumulated depreciation and amortization on finance and operating lease right-of-use leases	$ 2,641	$ 0
Accumulated depreciation of property and equipment	$ 16,890	$ 15,671
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	254,513,522	189,383,924
Common stock, shares outstanding	254,513,522	189,383,924

Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue:
Net product sales	$ 44,130	$ 21,309	$ 78,176	$ 38,005
Cost of goods sold	5,367	3,135	9,422	5,750
Gross profit	38,763	18,174	68,754	32,255
Operating expenses:
Research and development	70,981	34,660	135,574	75,458
Selling, general and administrative	42,578	29,172	86,881	56,568
Changes in fair value of contingent consideration payable	480	300	1,863	1,400
Depreciation and amortization	1,154	973	2,145	1,942
Total operating expenses	115,193	65,105	226,463	135,368
Loss from operations	(76,430)	(46,931)	(157,709)	(103,113)
Other income (expense):
Interest income	2,599	2,913	5,238	4,650
Interest expense	(4,625)	(4,560)	(11,079)	(9,048)
Loss on exchange of convertible notes	(4,501)	0	(40,624)	0
Change in fair value of derivatives	0	(7,600)	0	(2,739)
Other (expense) income	(877)	(5,316)	209	(2,554)
Loss before income tax	(83,834)	(61,494)	(203,965)	(112,804)
Income tax benefit	(717)	(339)	(885)	1,053
Net loss attributable to common stockholders	$ (84,551)	$ (61,833)	$ (204,850)	$ (111,751)
Net loss attributable to common stockholders per common share - basic and diluted (in dollars per share)	$ (0.36)	$ (0.33)	$ (0.91)	$ (0.61)
Weighted-average common shares outstanding - basic and diluted (in shares)	238,089,824	188,621,423	225,848,013	182,303,128

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net loss	$ (84,551)	$ (61,833)	$ (204,850)	$ (111,751)
Other comprehensive (loss) gain:
Foreign currency translation adjustment gain (loss), net of tax impact of $(30), $(109), $(30) and $(109), respectively	1,881	2,308	77	503
Unrealized (loss) gain on available-for-sale securities, net of tax impact of $(220), $0, $(220) and $0, respectively	(22)	422	562	(19)
Other comprehensive income (loss)	1,859	2,730	639	484
Comprehensive loss	$ (82,692)	$ (59,103)	$ (204,211)	$ (111,267)

- 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	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Foreign currency translation adjustment, tax (expense) benefit	$ (30)	$ (109)	$ (30)	$ (109)
Available-for-sale securities, tax expense (benefit)	$ (220)	$ 0	$ (220)	$ 0

Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Outstanding warrants, convertible to common stock	Other Comprehensive Gain (Loss)	Accumulated Deficit
Increase (Decrease) in Stockholders' Equity
Reclassification upon ASU 2018-02 adoption	$ 0				$ (383)	$ 383
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)		560,721
Stock issued from exercise of stock options, net	3,978	$ 6	3,972
Stock issued from equity financing (in shares)		20,239,839
Stock issued from equity financing	294,584	$ 202	294,382
Restricted stock tax vesting (in shares)		181,868
Restricted stock tax vesting	(1,912)		(1,912)
Stock-based compensation	7,478		7,478
Change in fair value of derivatives	(83,199)		(83,199)
Unrealized holding gain (loss) on available-for-sale securities	(441)				(441)
Foreign currency translation adjustment	(1,805)				(1,805)
Net loss	(49,916)					(49,916)
Balance (in shares) at Mar. 31, 2018		187,972,218
Balance at Mar. 31, 2018	521,617	$ 1,929	1,621,479	16,076	(4,724)	(1,113,143)
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
Unrealized holding gain (loss) on available-for-sale securities	(19)
Foreign currency translation adjustment	503
Net loss	(111,751)
Balance (in shares) at Jun. 30, 2018		189,053,214
Balance at Jun. 30, 2018	561,895	$ 1,939	1,723,865	13,063	(1,994)	(1,174,978)
Balance (in shares) at Mar. 31, 2018		187,972,218
Balance at Mar. 31, 2018	521,617	$ 1,929	1,621,479	16,076	(4,724)	(1,113,143)
Increase (Decrease) in Stockholders' Equity
Stock issued from exercise of stock options, net (in shares)		542,056
Stock issued from exercise of stock options, net	3,602	$ 5	3,597
Restricted stock tax vesting (in shares)		85,726
Restricted stock tax vesting	(115)		(115)
Stock-based compensation	6,341		6,341
Warrants exercised (in shares)		453,214
Warrants exercised	3,617	$ 5	6,625	(3,013)
Change in fair value of derivatives	85,938		85,938
Unrealized holding gain (loss) on available-for-sale securities	422				422
Foreign currency translation adjustment	2,308				2,308
Net loss	(61,833)					(61,833)
Balance (in shares) at Jun. 30, 2018		189,053,214
Balance at Jun. 30, 2018	$ 561,895	$ 1,939	1,723,865	13,063	(1,994)	(1,174,978)
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)		578,451
Stock issued from exercise of stock options, net	3,953	$ 6	3,947
Restricted stock tax vesting (in shares)		301,058
Restricted stock tax vesting	(1,940)		(1,940)
Stock issued for contingent consideration (in shares)		771,804
Stock issued for contingent consideration	9,316	$ 8	9,308
Stock-based compensation	12,744		12,744
Warrants exercised (in shares)		101,787
Warrants exercised	812	$ 1	1,487	(676)
Equity component of the convertible notes (in shares)		39,043,690
Equity component of the convertible notes	190,758	$ 390	190,368
Termination of capped call confirmations	14,632		14,632
Unrealized holding gain (loss) on available-for-sale securities	584				584
Foreign currency translation adjustment	(1,804)				(1,804)
Net loss	(120,299)					(120,299)
Balance (in shares) at Mar. 31, 2019		230,180,714
Balance at Mar. 31, 2019	$ 451,668	$ 2,347	1,970,607	12,387	(1,152)	(1,532,521)
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
Unrealized holding gain (loss) on available-for-sale securities	562
Foreign currency translation adjustment	77
Net loss	$ (204,850)
Balance (in shares) at Jun. 30, 2019	254,513,522	254,513,522
Balance at Jun. 30, 2019	$ 600,058	$ 2,589	2,201,447	12,387	707	(1,617,072)
Balance (in shares) at Mar. 31, 2019		230,180,714
Balance at Mar. 31, 2019	451,668	$ 2,347	1,970,607	12,387	(1,152)	(1,532,521)
Increase (Decrease) in Stockholders' Equity
Stock issued from exercise of stock options, net (in shares)		561,177
Stock issued from exercise of stock options, net	$ 2,807	$ 5	2,802
Stock issued from equity financing (in shares)	18,700,000	18,720,930
Stock issued from equity financing	$ 188,994	$ 187	188,807
Restricted stock tax vesting (in shares)		99,252
Restricted stock tax vesting	(615)		(615)
Stock-based compensation	9,935		9,935
Equity component of the convertible notes (in shares)		4,951,449
Equity component of the convertible notes	24,718	$ 50	24,668
Termination of capped call confirmations	5,243		5,243
Unrealized holding gain (loss) on available-for-sale securities	(22)				(22)
Foreign currency translation adjustment	1,881				1,881
Net loss	$ (84,551)					(84,551)
Balance (in shares) at Jun. 30, 2019	254,513,522	254,513,522
Balance at Jun. 30, 2019	$ 600,058	$ 2,589	$ 2,201,447	$ 12,387	$ 707	$ (1,617,072)

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Operating activities
Net loss	$ (204,850)	$ (111,751)
Adjustments to reconcile net loss to net cash used in operating activities:
Amortization of debt discount and deferred financing	2,104	5,273
Depreciation and amortization	2,145	1,942
Stock-based compensation	22,679	13,819
Loss on exchange of convertible debt	40,624	0
Change in fair value of derivatives	0	2,739
Non-cash changes in the fair value of contingent consideration payable	1,863	1,400
Foreign currency remeasurement loss	530	2,107
Changes in operating assets and liabilities:
Accounts receivable	(6,829)	(6,043)
Inventories	(1,908)	(3,449)
Prepaid expenses and other current assets	(3,523)	4,584
Accounts payable and accrued expenses	12,453	(11,801)
Other non-current assets and liabilities	(819)	(336)
Deferred reimbursements	(1,500)	(5,000)
Net cash used in operating activities	(137,031)	(106,516)
Investing activities
Sale and redemption of marketable securities	261,425	210,239
Purchases of marketable securities	(191,318)	(380,234)
Capital expenditures	(5,110)	(1,881)
Net cash provided by (used in) investing activities	64,997	(171,876)
Financing activities
Proceeds from issuance of common stock, net of issuance costs	188,994	294,584
Payment of finance leases	(98)
Payment of finance leases		(142)
Purchase of vested restricted stock units	(2,555)	(2,027)
Proceeds from termination of capped call confirmations	19,875	0
Proceeds from exercise of stock options	6,760	7,580
Proceeds of exercise of warrants	812	3,617
Net cash provided by financing activities	213,788	303,612
Effect of exchange rate changes on cash, cash equivalents, and restricted cash	(941)	(1,016)
Net increase in cash, cash equivalents, and restricted cash	140,813	24,204
Cash, cash equivalents, and restricted cash at beginning of period	82,375	51,237
Cash, cash equivalents, and restricted cash at end of period	223,188	75,441
Cash paid during the period for interest
Cash paid during the period for interest	9,302	3,774
Capital expenditures, unpaid	837	0
Capital expenditures funded by capital lease	0	81
Payment of contingent consideration in shares	$ 9,316	$ 0

Business	6 Months Ended
Business	Jun. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Business	Business Amicus Therapeutics, Inc. (the "Company") is a global patient-dedicated biotechnology company engaged in the discovery, development, and commercialization of a diverse set of novel treatments for patients living with rare metabolic diseases. With one 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."), and Japan, with additional approvals granted and applications pending in several other geographies. During the third quarter of 2018, the Company initiated the commercial launch of Galafold^® in the U.S. for the treatment of adult patients with a confirmed diagnosis of Fabry disease and an amenable genetic variant. 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. 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 a recently expanded collaboration with the University of Pennsylvania ("Penn"). The Company's pipeline includes gene therapy programs in rare, neurologic lysosomal disorders ("LDs") with programs in CLN6, CLN3, and CLN8 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 rare diseases, including Rett Syndrome, Angelman Syndrome, Myotonic Dystophy, and select other muscular dystrophies. 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 six months ended June 30, 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 common stock, par value $0.01 per share. The Company had an accumulated deficit of $1.6 billion as of June 30, 2019 and anticipates incurring losses through the fiscal year ending December 31, 2019 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 2021. 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

6 Months Ended

Jun. 30, 2019

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Basis of Presentation

Consolidation

The consolidated financial statements include the accounts of the Company and its subsidiaries. Intercompany accounts and transactions have been eliminated in consolidation.

Foreign Currency Transactions

Use of Estimates

Reclassification

Certain prior year amounts have been reclassified for comparative purposes. The reclassifications did not affect results of operations, net assets, or cash flows.

Cash, Cash Equivalents, Marketable Securities, and Restricted Cash

Concentration of Credit Risk

Revenue Recognition

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



	Three Months Ended June 30,				Six Months Ended June 30,
(in thousands)	2019		2018		2019		2018
U.S.	$	12,181	$	—	$	21,249	$	—
Ex-U.S.	31,949		21,309		56,927		38,005
Total net product sales	$	44,130	$	21,309	$	78,176	$	38,005

Inventories and Cost of Goods Sold

Leases

Recent Accounting Developments - Guidance Adopted in 2019

Recent Accounting Developments - Guidance Not Yet Adopted

Cash, Cash Equivalents, Marketable Securities and Restricted Cash

6 Months Ended

Jun. 30, 2019

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

Cash, Cash Equivalents, Marketable Securities and Restricted Cash

Cash, Cash Equivalents, Marketable Securities, and Restricted Cash

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



	As of June 30, 2019
(in thousands)	Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Cash and cash equivalents	$	220,578	$	—	$	—		$	220,578
Corporate debt securities	169,425		148		(15		)	169,558
Commercial paper	111,872		156		(2		)	112,026
Asset-backed securities	73,025		68		—			73,093
Money market	350		—		—			350
Certificates of deposit	51		—		—			51
	$	575,301	$	372	$	(17	)	$	575,656
Included in cash and cash equivalents	$	220,578	$	—	$	—		$	220,578
Included in marketable securities	354,723		372		(17		)	355,078
Total cash, cash equivalents, and marketable securities	$	575,301	$	372	$	(17	)	$	575,656



	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



(in thousands)	June 30, 2019		December 31, 2018		June 30, 2018		December 31, 2017
Cash and cash equivalents	$	220,578	$	79,749	$	73,311	$	49,060
Restricted cash	2,610		2,626		2,130		2,177
Cash, cash equivalents, and restricted cash shown in the Consolidated Statements of Cash Flows	$	223,188	$	82,375	$	75,441	$	51,237

Inventories

6 Months Ended

Jun. 30, 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)	June 30, 2019		December 31, 2018
Raw materials	$	4,018	$	1,291
Work-in-process	3,320		3,485
Finished goods	3,057		3,614
Total inventories	$	10,395	$	8,390

The Company recorded a reserve for inventory of $0.2 million as of June 30, 2019 and December 31, 2018.

Debt

6 Months Ended

Jun. 30, 2019

Debt Disclosure [Abstract]

Debt

Senior Secured Term Loan due 2023

Convertible Notes due 2023

During the six months ended June 30, 2019, the Company also terminated the Capped Call Confirmations related to the exchange of the Convertible Notes for proceeds of $19.9 million.

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



Liability component (in thousands)			June 30, 2019			December 31, 2018
Principal			$	152,825		$	400,000
Less: debt discount	⁽¹⁾		(3,373		)	(74,145		)
Less: deferred financing		⁽¹⁾	(388		)	(4,115		)
Net carrying value of the debt			$	149,064		$	321,740

______________________________________

The following table sets forth total interest expense recognized related to the Convertible Notes and Senior Secured Term Loan for the three and six months ended June 30, 2019 and 2018, respectively:



	Three Months Ended June 30,				Six Months Ended June 30,
Interest component (in thousands)	2019		2018		2019		2018
Contractual interest expense	$	4,146	$	1,888	$	8,959	$	3,775
Amortization of debt discount	423		2,539		1,982		5,011
Amortization of deferred financing	39		133		122		262
Total	$	4,608	$	4,560	$	11,063	$	9,048

Stockholders' Equity	6 Months Ended
Stockholders' Equity	Jun. 30, 2019
Equity [Abstract]
Stockholders' Equity	Stockholders' Equity During the six months ended June 30, 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 5. Debt'' during the six months ended June 30, 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. As discussed in "— Note 8. 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.

Share-Based Compensation

6 Months Ended

Jun. 30, 2019

Share-based Payment Arrangement [Abstract]

Share-Based Compensation

Stock Option Grants

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:



		Three Months Ended June 30,						Six Months Ended June 30,
		2019			2018			2019			2018
Expected stock price volatility		74.2		%	81.1		%	74.2		%	81.2		%
Risk free interest rate		2.0		%	2.8		%	2.4		%	2.4		%
Expected life of options (years)	⁽¹⁾	5.68			5.62			5.68			5.62
Expected annual dividend per share		$	—		$	—		$	—		$	—

______________________________________

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

A summary of the Company's stock options for the six months ended June 30, 2019 were as follows:



	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life	Aggregate Intrinsic Value
	(in thousands)					(in millions)
Options outstanding, December 31, 2018	15,810		$	8.63
Granted	3,683		$	10.36
Exercised	(1,139	)	$	5.93
Forfeited	(445	)	$	11.02
Expired	(60	)	$	13.61
Options outstanding, June 30, 2019	17,849		$	9.09	6.8 years	$	68.7
Vested and unvested expected to vest, June 30, 2019	16,975		$	8.99	6.7 years	$	66.8
Exercisable at June 30, 2019	10,624		$	8.14	5.5 years	$	50.1

Restricted Stock Units and Performance-Based Restricted Stock Units (collectively "RSUs")



	Number of Shares		Weighted Average Grant Date Fair Value		Weighted Average Remaining Years	Aggregate Intrinsic Value
	(in thousands)					(in millions)
Non-vested units as of December 31, 2018	3,712		$	10.59
Granted	3,262		$	11.02
Vested	(788	)	$	9.28
Forfeited	(301	)	$	10.32
Non-vested units as of June 30, 2019	5,885		$	11.09	2.7 years	$	73.5

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:



	Three Months Ended June 30,				Six Months Ended June 30,
(in thousands)	2019		2018		2019		2018
Equity compensation expense recognized in:
Research and development expense	$	3,952	$	2,641	$	8,984	$	5,698
Selling, general, and administrative expense	5,983		3,700		13,695		8,121
Total equity compensation expense	$	9,935	$	6,341	$	22,679	$	13,819

Assets and Liabilities Measured at Fair Value

6 Months Ended

Jun. 30, 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.



(in thousands)	Level 2		Total
Assets:
Commercial paper	$	112,026	$	112,026
Asset-backed securities	73,093		73,093
Corporate debt securities	169,558		169,558
Money market funds	4,224		4,224
	$	358,901	$	358,901



	Level 2		Level 3		Total
Liabilities:
Contingent consideration payable	$	—	$	21,247	$	21,247
Deferred compensation plan liability	3,874		—		3,874
	$	3,874	$	21,247	$	25,121



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



	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 did not have any Level 3 assets as of June 30, 2019 or December 31, 2018.

Cash, Money Market Funds, and Marketable Securities

Contingent Consideration Payable

The following significant unobservable inputs were used in the valuation of the contingent consideration payable of Callidus for the ATB200 Pompe program:



Contingent Consideration Liability	Fair Value as of June 30, 2019	Valuation Technique	Unobservable Input	Range
	(in thousands)

			Discount rate	10.1%

Clinical and regulatory milestones	$20,999	Probability weighted discounted cash flow	Probability of achievement of milestones	75%-78%

			Projected year of payments	2021-2022

The following table shows the change in the balance of contingent consideration payable for the three and six months ended June 30, 2019 and 2018, respectively:



	Three Months Ended June 30,				Six Months Ended June 30,
(in thousands)	2019		2018		2019			2018
Balance, beginning of the period	$	20,767	$	26,500	$	28,700		$	25,400
Payment of contingent consideration in stock	—		—		(9,316		)	—
Changes in fair value during the period, included in the Consolidated Statements of Operations	480		300		1,863			1,400
Balance, end of the period	$	21,247	$	26,800	$	21,247		$	26,800

Deferred Compensation Plan - Investment and Liability

- Definition

+ References + Details

Leases

6 Months Ended

Jun. 30, 2019

Leases [Abstract]

Leases

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)	June 30, 2019
Operating lease ROU asset	$	35,052

Current portion of the operating lease liabilities	$	2,678
Non-current portion of the operating lease liabilities	36,259
Total operating lease liability	$	38,937

Weighted-average remaining lease terms (years)	14.8
Weighted-average discount rate	12.9		%

At June 30, 2019, the future minimum lease payments were as follows:



( in thousands)	Operating Leases
2019 (excludes the six months ended June 30, 2019)	$	2,781
2020	9,647
2021	10,566
2022	10,411
2023	10,789
Thereafter	174,673
Total lease payments	$	218,867
Less lease incentives	(28,939		)
Less imputed interest	(150,991		)
Total operating lease liability	$	38,937

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



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

Leases

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)	June 30, 2019
Operating lease ROU asset	$	35,052

Current portion of the operating lease liabilities	$	2,678
Non-current portion of the operating lease liabilities	36,259
Total operating lease liability	$	38,937

Weighted-average remaining lease terms (years)	14.8
Weighted-average discount rate	12.9		%

At June 30, 2019, the future minimum lease payments were as follows:



( in thousands)	Operating Leases
2019 (excludes the six months ended June 30, 2019)	$	2,781
2020	9,647
2021	10,566
2022	10,411
2023	10,789
Thereafter	174,673
Total lease payments	$	218,867
Less lease incentives	(28,939		)
Less imputed interest	(150,991		)
Total operating lease liability	$	38,937

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



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

Basic and Diluted Net Loss per Common Share

6 Months Ended

Jun. 30, 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:



	Three Months Ended June 30,						Six Months Ended June 30,
(in thousands, except per share amounts)	2019			2018			2019			2018
Numerator:
Net loss attributable to common stockholders	$	(84,551	)	$	(61,833	)	$	(204,850	)	$	(111,751	)
Denominator:
Weighted average common shares outstanding — basic and diluted	238,089,824			188,621,423			225,848,013			182,303,128

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:



	As of June 30,
(in thousands)	2019	2018
Options to purchase common stock	17,849	15,869
Convertible notes	462	40,850
Outstanding warrants, convertible to common stock	2,555	2,657
Unvested restricted stock units	5,885	3,556
Vested restricted stock units, unissued	227	111
Total number of potentially issuable shares	26,978	63,043

Summary of Significant Accounting Policies (Policies)	6 Months Ended
Summary of Significant Accounting Policies (Policies)	Jun. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The Company has prepared the accompanying unaudited consolidated financial statements in accordance with accounting principles generally accepted in the United States of America ("U.S. GAAP") for interim financial information and with the instructions to Form 10-Q and Article 10-01 of Regulation S-X. Accordingly, they do not include all of the information and disclosures required by U.S. GAAP for complete financial statements. In the opinion of management, the accompanying unaudited financial statements reflect all adjustments, which include only normal recurring adjustments, necessary to present fairly the Company's interim financial information. The accompanying unaudited consolidated financial statements and related notes should be read in conjunction with the Company's financial statements and related notes as contained in the Company's Annual Report on Form 10-K for the fiscal year ended December 31, 2018. For a complete description of the Company's accounting policies, please refer to the Annual Report on Form 10-K for the fiscal year ended December 31, 2018.
Consolidation	Consolidation The consolidated financial statements include the accounts of the Company and its subsidiaries. Intercompany accounts and transactions have been 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.
Reclassification	Reclassification Certain prior year amounts have been reclassified for comparative purposes. The reclassifications did not affect results of operations, net assets, or cash flows.
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 Consolidated Balance Sheets. Unrealized holding gains and losses are reported within comprehensive income (loss) in the Consolidated 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 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 cash and cash equivalents or its 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 June 30, 2019 have arisen from product sales primarily in the E.U. and 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.
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. 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 revenue from the sale of Galafold^® is 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 goods sold 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. A portion of the inventory available-for-sale was expensed as research and development costs prior to regulatory approval and as such the cost of goods sold and related gross margins are not necessarily indicative of future cost of goods sold and gross margin.
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 9. Leases" and "—Note 2. Summary of Significant Accounting Policies, Recent Accounting Developments - Guidance Adopted in 2019."
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. In August 2018, the Securities Exchange Commission ("SEC") issued Final Rule 33-10532, Disclosure Update and Simplification, which amends certain disclosure requirements that were redundant, duplicative, overlapping, or superseded by other SEC disclosure requirements. The amendments generally eliminated or otherwise reduced certain disclosure requirements of various SEC rules and regulations. However, in some cases, the amendments require additional information to be disclosed, including changes in stockholders' equity in interim periods. The rule was effective 30 days after its publication in the Federal Register. The rule was posted on October 4, 2018. On September 25, 2018, the SEC released guidance advising it will not object to a registrant adopting the requirement to include changes in stockholders' equity in the Form 10-Q for the first quarter beginning after the effective date of the rule. The Company adopted the guidance for the period ended March 31, 2019. Recent Accounting Developments - Guidance Not Yet Adopted ASU 2018-13— In August 2018, the FASB issued ASU 2018-13, 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 changes (i) 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. Early adoption is permitted. An entity is permitted to early adopt any removed or modified disclosures upon issuance of ASU 2018-13 and delay adoption of the additional disclosures until their effective date. The Company is currently assessing the impact that this standard will have on its consolidated financial statements upon adoption. 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. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The Company is currently assessing the impact that this standard will have on its consolidated financial statements upon adoption. 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 is currently assessing the impact that this standard will have on its consolidated financial statements upon adoption.

Summary of Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2019

Accounting Policies [Abstract]

Disaggregation of Revenue

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



	Three Months Ended June 30,				Six Months Ended June 30,
(in thousands)	2019		2018		2019		2018
U.S.	$	12,181	$	—	$	21,249	$	—
Ex-U.S.	31,949		21,309		56,927		38,005
Total net product sales	$	44,130	$	21,309	$	78,176	$	38,005

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

6 Months Ended

Jun. 30, 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 June 30, 2019
(in thousands)	Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Cash and cash equivalents	$	220,578	$	—	$	—		$	220,578
Corporate debt securities	169,425		148		(15		)	169,558
Commercial paper	111,872		156		(2		)	112,026
Asset-backed securities	73,025		68		—			73,093
Money market	350		—		—			350
Certificates of deposit	51		—		—			51
	$	575,301	$	372	$	(17	)	$	575,656
Included in cash and cash equivalents	$	220,578	$	—	$	—		$	220,578
Included in marketable securities	354,723		372		(17		)	355,078
Total cash, cash equivalents, and marketable securities	$	575,301	$	372	$	(17	)	$	575,656



	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 restricted cash and cash equivalents



(in thousands)	June 30, 2019		December 31, 2018		June 30, 2018		December 31, 2017
Cash and cash equivalents	$	220,578	$	79,749	$	73,311	$	49,060
Restricted cash	2,610		2,626		2,130		2,177
Cash, cash equivalents, and restricted cash shown in the Consolidated Statements of Cash Flows	$	223,188	$	82,375	$	75,441	$	51,237

Inventories (Tables)

6 Months Ended

Jun. 30, 2019

Inventory Disclosure [Abstract]

Schedule of inventories for the period

The following table summarizes the components of inventories:



(in thousands)	June 30, 2019		December 31, 2018
Raw materials	$	4,018	$	1,291
Work-in-process	3,320		3,485
Finished goods	3,057		3,614
Total inventories	$	10,395	$	8,390

Debt (Tables)

6 Months Ended

Jun. 30, 2019

Debt Disclosure [Abstract]

Schedule of liability components of the Convertible Notes

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



Liability component (in thousands)			June 30, 2019			December 31, 2018
Principal			$	152,825		$	400,000
Less: debt discount	⁽¹⁾		(3,373		)	(74,145		)
Less: deferred financing		⁽¹⁾	(388		)	(4,115		)
Net carrying value of the debt			$	149,064		$	321,740

______________________________________

Components of total interest expense recognized related to the Convertible Notes

The following table sets forth total interest expense recognized related to the Convertible Notes and Senior Secured Term Loan for the three and six months ended June 30, 2019 and 2018, respectively:



	Three Months Ended June 30,				Six Months Ended June 30,
Interest component (in thousands)	2019		2018		2019		2018
Contractual interest expense	$	4,146	$	1,888	$	8,959	$	3,775
Amortization of debt discount	423		2,539		1,982		5,011
Amortization of deferred financing	39		133		122		262
Total	$	4,608	$	4,560	$	11,063	$	9,048

Share-Based Compensation (Tables)

6 Months Ended

Jun. 30, 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:



		Three Months Ended June 30,						Six Months Ended June 30,
		2019			2018			2019			2018
Expected stock price volatility		74.2		%	81.1		%	74.2		%	81.2		%
Risk free interest rate		2.0		%	2.8		%	2.4		%	2.4		%
Expected life of options (years)	⁽¹⁾	5.68			5.62			5.68			5.62
Expected annual dividend per share		$	—		$	—		$	—		$	—

______________________________________

⁽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 six months ended June 30, 2019 were as follows:



	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life	Aggregate Intrinsic Value
	(in thousands)					(in millions)
Options outstanding, December 31, 2018	15,810		$	8.63
Granted	3,683		$	10.36
Exercised	(1,139	)	$	5.93
Forfeited	(445	)	$	11.02
Expired	(60	)	$	13.61
Options outstanding, June 30, 2019	17,849		$	9.09	6.8 years	$	68.7
Vested and unvested expected to vest, June 30, 2019	16,975		$	8.99	6.7 years	$	66.8
Exercisable at June 30, 2019	10,624		$	8.14	5.5 years	$	50.1

Schedule of Non-Vested RSU Activity under the Plan

A summary of non-vested RSU activity under the Plan for the six months ended June 30, 2019 is as follows:



	Number of Shares		Weighted Average Grant Date Fair Value		Weighted Average Remaining Years	Aggregate Intrinsic Value
	(in thousands)					(in millions)
Non-vested units as of December 31, 2018	3,712		$	10.59
Granted	3,262		$	11.02
Vested	(788	)	$	9.28
Forfeited	(301	)	$	10.32
Non-vested units as of June 30, 2019	5,885		$	11.09	2.7 years	$	73.5

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:



	Three Months Ended June 30,				Six Months Ended June 30,
(in thousands)	2019		2018		2019		2018
Equity compensation expense recognized in:
Research and development expense	$	3,952	$	2,641	$	8,984	$	5,698
Selling, general, and administrative expense	5,983		3,700		13,695		8,121
Total equity compensation expense	$	9,935	$	6,341	$	22,679	$	13,819

Assets and Liabilities Measured at Fair Value (Tables)

6 Months Ended

Jun. 30, 2019

Fair Value Disclosures [Abstract]

Summary of assets and liabilities subject to fair value measurements



(in thousands)	Level 2		Total
Assets:
Commercial paper	$	112,026	$	112,026
Asset-backed securities	73,093		73,093
Corporate debt securities	169,558		169,558
Money market funds	4,224		4,224
	$	358,901	$	358,901



	Level 2		Level 3		Total
Liabilities:
Contingent consideration payable	$	—	$	21,247	$	21,247
Deferred compensation plan liability	3,874		—		3,874
	$	3,874	$	21,247	$	25,121



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



	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

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Schedule of changes in contingent consideration payable

The following table shows the change in the balance of contingent consideration payable for the three and six months ended June 30, 2019 and 2018, respectively:



	Three Months Ended June 30,				Six Months Ended June 30,
(in thousands)	2019		2018		2019			2018
Balance, beginning of the period	$	20,767	$	26,500	$	28,700		$	25,400
Payment of contingent consideration in stock	—		—		(9,316		)	—
Changes in fair value during the period, included in the Consolidated Statements of Operations	480		300		1,863			1,400
Balance, end of the period	$	21,247	$	26,800	$	21,247		$	26,800

Callidus Biopharma Inc

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

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 ATB200 Pompe program:



Contingent Consideration Liability	Fair Value as of June 30, 2019	Valuation Technique	Unobservable Input	Range
	(in thousands)

			Discount rate	10.1%

Clinical and regulatory milestones	$20,999	Probability weighted discounted cash flow	Probability of achievement of milestones	75%-78%

			Projected year of payments	2021-2022

- Definition

+ References + Details

Leases (Tables)

6 Months Ended

Jun. 30, 2019

Leases [Abstract]

Lease costs

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



(in thousands, except year and discount rate amounts)	June 30, 2019
Operating lease ROU asset	$	35,052

Current portion of the operating lease liabilities	$	2,678
Non-current portion of the operating lease liabilities	36,259
Total operating lease liability	$	38,937

Weighted-average remaining lease terms (years)	14.8
Weighted-average discount rate	12.9		%

Future minimum lease payments, operating leases

At June 30, 2019, the future minimum lease payments were as follows:



( in thousands)	Operating Leases
2019 (excludes the six months ended June 30, 2019)	$	2,781
2020	9,647
2021	10,566
2022	10,411
2023	10,789
Thereafter	174,673
Total lease payments	$	218,867
Less lease incentives	(28,939		)
Less imputed interest	(150,991		)
Total operating lease liability	$	38,937

Schedule of future minimum lease payments

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



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

Basic and Diluted Net Loss per Common Share (Tables)

6 Months Ended

Jun. 30, 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:



	Three Months Ended June 30,						Six Months Ended June 30,
(in thousands, except per share amounts)	2019			2018			2019			2018
Numerator:
Net loss attributable to common stockholders	$	(84,551	)	$	(61,833	)	$	(204,850	)	$	(111,751	)
Denominator:
Weighted average common shares outstanding — basic and diluted	238,089,824			188,621,423			225,848,013			182,303,128

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:



	As of June 30,
(in thousands)	2019	2018
Options to purchase common stock	17,849	15,869
Convertible notes	462	40,850
Outstanding warrants, convertible to common stock	2,555	2,657
Unvested restricted stock units	5,885	3,556
Vested restricted stock units, unissued	227	111
Total number of potentially issuable shares	26,978	63,043

Business (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Class of Stock [Line Items]
Common stock issued from underwriting agreement (in shares)	18.7
Proceeds from issuance of common stock, net of issuance costs	$ 189,000	$ 188,994	$ 294,584
Exchange agreement, aggregate principal amount	$ 247,200	$ 247,200
Shares authorized for issuance (in shares)	44.0	44.0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01		$ 0.01
Accumulated deficit	$ (1,617,072)	$ (1,617,072)		$ (1,412,222)
Underwritten Offering
Class of Stock [Line Items]
Stock issued (in dollars per share)	$ 10.75	$ 10.75

Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for doubtful accounts receivable	$ 200		$ 200
Net product sales	44,130	$ 21,309	78,176	$ 38,005
Operating lease, liability	38,937		38,937
Operating lease ROU asset	35,052		35,052
ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, liability					$ 17,600
Operating lease ROU asset	17,600		17,600
U.S.
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net product sales	12,181	0	21,249	0
Ex-U.S.
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net product sales	$ 31,949	$ 21,309	$ 56,927	$ 38,005

Cash, Cash Equivalents, Marketable Securities and Restricted Cash - Components (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Cash, Money Market Funds, and Marketable Securities
Cash and cash equivalents	$ 220,578	$ 79,749	$ 73,311	$ 49,060
Fair value, Available-for-sale debt securities	355,078	424,403
Fair Value, Cash balances	220,578	79,749
Cost, available-for-sale securities	354,723	424,830
Gross unrealized gain, available-for-sale securities	372	11
Gross unrealized loss, available-for-sale securities	(17)	(438)
Cost, Cash balances and available-for-sale securities	575,301	504,579
Gross unrealized gain, Cash balances and available-for-sale securities	372	11
Gross unrealized loss, Cash balances and available-for-sale securities	(17)	(438)
Fair value, Cash balances and available-for-sale securities	575,656	504,152
Corporate debt securities
Cash, Money Market Funds, and Marketable Securities
Fair value, Available-for-sale debt securities	169,558	240,726
Cost, available-for-sale securities	169,425	240,969
Gross unrealized gain, available-for-sale securities	148	7
Gross unrealized loss, available-for-sale securities	(15)	(250)
Commercial paper
Cash, Money Market Funds, and Marketable Securities
Fair value, Available-for-sale debt securities	112,026	115,141
Cost, available-for-sale securities	111,872	115,245
Gross unrealized gain, available-for-sale securities	156	0
Gross unrealized loss, available-for-sale securities	(2)	(104)
Asset-backed securities
Cash, Money Market Funds, and Marketable Securities
Fair value, Available-for-sale debt securities	73,093	68,135
Cost, available-for-sale securities	73,025	68,215
Gross unrealized gain, available-for-sale securities	68	4
Gross unrealized loss, available-for-sale securities	0	(84)
Money market
Cash, Money Market Funds, and Marketable Securities
Fair value, Available-for-sale debt securities	350	350
Cost, available-for-sale securities	350	350
Gross unrealized gain, available-for-sale securities	0	0
Gross unrealized loss, available-for-sale securities	0	0
Certificates of deposit
Cash, Money Market Funds, and Marketable Securities
Fair value, Available-for-sale debt securities	51	51
Cost, available-for-sale securities	51	51
Gross unrealized gain, available-for-sale securities	0	0
Gross unrealized loss, available-for-sale securities	$ 0	$ 0

Cash, Cash Equivalents, Marketable Securities and Restricted Cash - Additional Information (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Realized gain (loss) on debt securities	$ 0	$ 0
Fair value of available-for-sale debt securities in unrealized loss positions	38,500,000	403,100,000
Cash and cash equivalents	220,578,000	79,749,000	$ 73,311,000	$ 49,060,000
Restricted cash	2,610,000	2,626,000	2,130,000	2,177,000
Cash, cash equivalents, and restricted cash shown in the Consolidated Statements of Cash Flows	$ 223,188,000	$ 82,375,000	$ 75,441,000	$ 51,237,000

Inventories (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Inventory Disclosure [Abstract]
Raw materials	$ 4,018	$ 1,291
Work-in-process	3,320	3,485
Finished goods	3,057	3,614
Total inventories	10,395	8,390
Reserve for inventory	$ 200	$ 200

Debt (Details)			1 Months Ended		3 Months Ended			6 Months Ended
Debt (Details)	Feb. 16, 2018 shares	Feb. 15, 2018 USD ($) shares	Sep. 30, 2018 USD ($)	Dec. 31, 2016 USD ($) day $ / shares shares	Jun. 30, 2019 USD ($) $ / shares shares	Mar. 31, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) $ / shares shares	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) $ / shares shares	Jun. 07, 2018 USD ($) shares
Convertible Debt
Common stock issued from underwriting agreement (in shares) \| shares					18,700,000
Derivative liability, noncurrent		$ 507,400,000
Change in fair value of derivatives							$ (7,600,000)		$ (2,700,000)
Common stock, shares authorized (in shares) \| shares					500,000,000			500,000,000		500,000,000	500,000,000
Derivative liabilities											$ 88,300,000
Other assets, current											$ 2,400,000
Exchange agreement, aggregate principal amount					$ 247,200,000			$ 247,200,000
Shares authorized for issuance (in shares) \| shares					44,000,000.0			44,000,000.0
Common stock, par value (in dollars per share) \| $ / shares					$ 0.01			$ 0.01		$ 0.01
Exchange agreement, accrued and unpaid interest								$ 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
Gain (loss) on exchange of convertible debt					(4,501,000)	$ (36,100,000)	0	(40,624,000)	0
Proceeds from capped call confirmations, exchange of convertible debt								$ 19,875,000	0
Common Stock Capped Call Confirmation
Convertible Debt
Derivative asset, noncurrent		$ 13,600,000
Common Stock
Convertible Debt
Common stock issued from underwriting agreement (in shares) \| shares	885,000	19,400,000
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
Convertible Debt
Threshold percentage								130.00%
Convertible Notes \| Convertible Senior Notes 2016, Due 2023
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 trading days				20 days
Threshold consecutive trading days \| day				30
Debt Instruments [Abstract]
Principal					152,825,000			$ 152,825,000		$ 400,000,000
Less: debt discount					(3,373,000)			(3,373,000)		(74,145,000)
Less: deferred financing					(388,000)			(388,000)		(4,115,000)
Net carrying value of the debt					(149,064,000)			(149,064,000)		$ (321,740,000)
Interest expense
Contractual interest expense					4,146,000		1,888,000	8,959,000	3,775,000
Amortization of debt discount					423,000		2,539,000	1,982,000	5,011,000
Amortization of deferred financing					39,000		133,000	122,000	262,000
Total					$ 4,608,000		$ 4,560,000	$ 11,063,000	$ 9,048,000
Convertible Notes \| Convertible Senior Notes 2016, Due 2023 \| 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%

Stockholders' Equity - Common Stock and Warrants (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended			6 Months Ended
	Feb. 16, 2018	Feb. 15, 2018	Jun. 30, 2019	Mar. 31, 2019	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Collaborative Agreements
Common stock issued from underwriting agreement (in shares)			18,700,000
Proceeds of exercise of warrants						$ 812	$ 3,617
Proceeds from issuance of common stock, net of issuance costs			$ 189,000			188,994	$ 294,584
Exchange agreement, aggregate principal amount			$ 247,200			$ 247,200
Shares authorized for issuance (in shares)			44,000,000.0			44,000,000.0
Common stock, par value (in dollars per share)			$ 0.01			$ 0.01		$ 0.01
Contingent consideration, milestone payment				$ 9,000
Milestone payment, stock issued as consideration						$ 9,000
Common Stock
Collaborative Agreements
Common stock issued from underwriting agreement (in shares)			18,720,930		20,239,839
Milestone payment, stock issued as consideration				$ 9,300
Underwritten Offering
Collaborative Agreements
Stock issued (in dollars per share)			$ 10.75			$ 10.75
Common Stock
Collaborative Agreements
Common stock issued from underwriting agreement (in shares)	885,000	19,400,000
Outstanding warrants, convertible to common stock
Collaborative Agreements
Common stock issued from underwriting agreement (in shares)						101,787
Proceeds of exercise of warrants						$ 800
Outstanding warrants, convertible to common stock \| Common Stock
Collaborative Agreements
Warrants exercise price (in dollars per share)			$ 7.98			$ 7.98

Share-Based Compensation - Weighted-average Assumptions (Details) - Options to purchase common stock - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected stock price volatility	74.20%	81.10%	74.20%	81.20%
Risk free interest rate	2.00%	2.80%	2.40%	2.40%
Expected life of options (years)	5 years 8 months 4 days	5 years 7 months 13 days	5 years 8 months 4 days	5 years 7 months 13 days
Expected annual dividend per share (in dollars per share)	$ 0	$ 0	$ 0	$ 0

Share-Based Compensation - Stock Option Activity (Details) - Options to purchase common stock - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	6 Months Ended
	Jun. 30, 2019
Number of Shares
Options outstanding (in shares)	15,810
Options, Granted (in shares)	3,683
Options, Exercised (in shares)	(1,139)
Options, Forfeited (in shares)	(445)
Options, Expired (in shares)	(60)
Options outstanding (in shares)	17,849
Options, Vested and unvested expected to vest (in shares)	16,975
Options, Exercisable (in shares)	10,624
Weighted Average Exercise Price
Option outstanding (in dollars per share)	$ 8.63
Options, Granted (in dollars per share)	10.36
Options, Exercised (in dollars per share)	5.93
Options, Forfeited (in dollars per share)	11.02
Options, Expired (in dollars per share)	13.61
Option outstanding (in dollars per share)	9.09
Options, Vested and unvested expected to vest (in dollars per share)	8.99
Options, Exercisable (in dollars per share)	$ 8.14
Additional Disclosures
Weighted average remaining contractual life, options outstanding	6 years 9 months 18 days
Weighted average remaining contractual life, options vested and unvested expected to vest	6 years 8 months 12 days
Weighted average remaining contractual life, options exercisable	5 years 6 months
Aggregate intrinsic value, options outstanding	$ 68.7
Aggregate intrinsic value, vested and unvested expected to vest	66.8
Aggregate intrinsic value, exercisable	$ 50.1

Share-Based Compensation - Narrative (Details) shares in Thousands, $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($) shares
Options to purchase common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation costs	$ 40.8
Unrecognized compensation costs, period for recognition (in years)	3 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]
Total unrecognized compensation costs	$ 47.5
Unrecognized compensation costs, period for recognition (in years)	3 years
RSUs vested and non-vested units expected to vest (in shares) \| shares	788

Share-Based Compensation - RSUs and PBRSUs Summary (Details) - Unvested restricted stock units - Stock Option Plan Amended Restated 2007 Equity Incentive Plan $ / shares in Units, shares in Thousands, $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($) $ / shares shares
Number of Shares
Non-vested units (in shares) \| shares	3,712
Granted (in shares) \| shares	3,262
Vested (in shares) \| shares	(788)
Forfeited (in shares) \| shares	(301)
Non-vested units (in shares) \| shares	5,885
Weighted Average Grant Date Fair Value
Non-vested units (in dollars per share) \| $ / shares	$ 10.59
Granted (in dollars per share) \| $ / shares	11.02
Vested (in dollars per share) \| $ / shares	9.28
Forfeited (in dollars per share) \| $ / shares	10.32
Non-vested units (in dollars per share) \| $ / shares	$ 11.09
Additional Disclosures
Non-vested units, weighted average remaining years	2 years 8 months 12 days
Non-vested units, aggregate intrinsic value \| $	$ 73.5

Share-Based Compensation - Expense Summary (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total equity compensation expense	$ 9,935	$ 6,341	$ 22,679	$ 13,819
Research and development expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total equity compensation expense	3,952	2,641	8,984	5,698
Selling, general, and administrative expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total equity compensation expense	$ 5,983	$ 3,700	$ 13,695	$ 8,121

Assets and Liabilities Measured at Fair Value - Components by Hierarchy Level (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Mar. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Assets:
Fair value of assets		$ 358,901	$ 427,084
Liabilities:
Contingent consideration payable		21,247	19,700
Deferred compensation plan liability		3,874	2,732
Fair value of liabilities		25,121	22,432
Exchange agreement, aggregate principal amount		247,200
Milestone payment, stock issued as consideration		9,000
Common Stock
Liabilities:
Milestone payment, stock issued as consideration	$ 9,300
ATB200 Pompe Program \| Contingent Consideration Liability Clinical and Regulatory Milestones \| Callidus Biopharma Inc
Liabilities:
Contingent consideration payable		$ 20,999
ATB200 Pompe Program \| Contingent Consideration Liability Clinical and Regulatory Milestones \| Probability of Milestone Achievement \| Minimum \| Callidus Biopharma Inc
Liabilities:
Discount rate		0.75
ATB200 Pompe Program \| Contingent Consideration Liability Clinical and Regulatory Milestones \| Probability of Milestone Achievement \| Maximum \| Callidus Biopharma Inc
Liabilities:
Discount rate		0.78
Commercial paper
Assets:
Fair value of assets		$ 112,026	115,141
Asset-backed securities
Assets:
Fair value of assets		73,093	68,135
Corporate debt securities
Assets:
Fair value of assets		169,558	240,726
Money market funds
Assets:
Fair value of assets		4,224	3,082
Level 2
Assets:
Fair value of assets		358,901	427,084
Liabilities:
Contingent consideration payable		0	0
Deferred compensation plan liability		3,874	2,732
Fair value of liabilities		3,874	2,732
Convertible debt, fair value		6,100
Level 2 \| Commercial paper
Assets:
Fair value of assets		112,026	115,141
Level 2 \| Asset-backed securities
Assets:
Fair value of assets		73,093	68,135
Level 2 \| Corporate debt securities
Assets:
Fair value of assets		169,558	240,726
Level 2 \| Money market funds
Assets:
Fair value of assets		4,224	3,082
Level 3
Liabilities:
Contingent consideration payable		21,247	19,700
Deferred compensation plan liability		0	0
Fair value of liabilities		$ 21,247	$ 19,700
Level 3 \| ATB200 Pompe Program \| Contingent Consideration Liability Clinical and Regulatory Milestones \| Probability Weighted Discounted Cash Flow \| Discount Rate \| Callidus Biopharma Inc
Liabilities:
Discount rate		0.101

Assets and Liabilities Measured at Fair Value - Level 3 Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of the period	$ 20,767	$ 26,500	$ 28,700	$ 25,400
Payment of contingent consideration in stock	0	0	(9,316)	0
Changes in fair value during the period, included in the Consolidated Statements of Operations	480	300	1,863	1,400
Balance, end of the period	$ 21,247	$ 26,800	$ 21,247	$ 26,800

Leases (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Leases (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Leases [Abstract]
Operating lease cost	$ 2,700	$ 4,800
Cash paid for amounts included in operating lease liabilities		2,400
Right-of-use assets obtained in exchange for new operating lease liabilities		200
Operating lease ROU asset	35,052	35,052
Current portion of the operating lease liabilities	2,678	2,678
Non-current portion of the operating lease liabilities	36,259	36,259
Total operating lease liability	$ 38,937	$ 38,937
Weighted-average remaining lease terms (years)	14 years 9 months 18 days	14 years 9 months 18 days
Weighted-average discount rate	12.90%	12.90%
Operating Leases
2019 (excludes the six months ended June 30, 2019)	$ 2,781	$ 2,781
2020	9,647	9,647
2021	10,566	10,566
2022	10,411	10,411
2023	10,789	10,789
Thereafter	174,673	174,673
Total	218,867	218,867
Less lease incentives	(28,939)	(28,939)
Less imputed interest	$ (150,991)	$ (150,991)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2019			$ 6,244
2020			4,063
2021			3,560
2022			3,371
2023			3,611
Thereafter			10,038
Total lease payments			$ 30,887

Basic and Diluted Net Loss per Common Share (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator:
Net loss attributable to common stockholders	$ (84,551)	$ (120,299)	$ (61,833)	$ (49,916)	$ (204,850)	$ (111,751)
Denominator:
Weighted-average common shares outstanding - basic and diluted (in shares)	238,089,824		188,621,423		225,848,013	182,303,128
Antidilutive securities excluded from computation of diluted earnings per share (in shares)					26,978,000	63,043,000
Options to purchase common stock
Denominator:
Antidilutive securities excluded from computation of diluted earnings per share (in shares)					17,849,000	15,869,000
Convertible notes
Denominator:
Antidilutive securities excluded from computation of diluted earnings per share (in shares)					462,000	40,850,000
Outstanding warrants, convertible to common stock
Denominator:
Antidilutive securities excluded from computation of diluted earnings per share (in shares)					2,555,000	2,657,000
Unvested restricted stock units
Denominator:
Antidilutive securities excluded from computation of diluted earnings per share (in shares)					5,885,000	3,556,000
Vested restricted stock units, unissued
Denominator:
Antidilutive securities excluded from computation of diluted earnings per share (in shares)					227,000	111,000