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Document and Entity Information - shares	3 Months Ended
Mar. 31, 2013	Apr. 26, 2013
Document and Entity Information
Entity Registrant Name	AMICUS THERAPEUTICS INC
Entity Central Index Key	0001178879
Document Type	10-Q
Document Period End Date	Mar. 31, 2013
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		49,631,672
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q1

Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 26,736	$ 33,971
Investments in marketable securities	58,015	65,151
Receivable due from GSK	1,308	3,225
Prepaid expenses and other current assets	1,753	2,270
Total current assets	87,812	104,617
Property and equipment, less accumulated depreciation and amortization of $8,501 and $8,872 at December 31, 2012 and March 31, 2013, respectively	4,962	5,029
Other non-current assets	442	442
Total Assets	93,216	110,088
Current liabilities:
Accounts payable and accrued expenses	6,427	8,845
Current portion of secured loan	398	398
Warrant liability	1,170
Total current liabilities	7,995	9,243
Deferred reimbursements	31,685	30,418
Warrant liability, non-current		908
Secured loan, less current portion	199	299
Commitments and contingencies
Stockholders' equity:
Common stock, $.01 par value, 125,000,000 shares authorized, 49,631,672 shares issued and outstanding at December 31, 2012, 125,000,000 shares authorized, 49,631,672 shares issued and outstanding at March 31, 2013	556	556
Additional paid-in capital	389,113	387,539
Accumulated other comprehensive income	15	14
Deficit accumulated during the development stage	(336,347)	(318,889)
Total stockholders' equity	53,337	69,220
Total Liabilities and Stockholders' Equity	$ 93,216	$ 110,088

Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		134 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013
Revenue:
Research revenue		$ 6,114	$ 57,493
Collaboration and milestone revenue		1,660	64,382
Total revenue		7,774	121,875
Operating Expenses:
Research and development	$ 11,989	14,004	327,882
General and administrative	4,823	4,095	137,436
Restructuring charges			1,522
Impairment of leasehold improvements			1,030
Depreciation and amortization	439	420	12,207
In-process research and development			418
Total operating expenses	17,251	18,519	480,495
Loss from operations	(17,251)	(10,745)	(358,620)
Other income (expenses):
Interest income	65	27	14,454
Interest expense	(10)	(43)	(2,432)
Change in fair value of warrant liability	(262)	(2,376)	1,291
Other income			252
Loss before tax benefit	(17,458)	(13,137)	(345,055)
Income tax benefit			8,708
Net loss	(17,458)	(13,137)	(336,347)
Deemed dividend			(19,424)
Preferred stock accretion			(802)
Net loss attributable to common stockholders	$ (17,458)	$ (13,137)	$ (356,573)
Net loss attributable to common stockholders per common share - basic and diluted (in dollars per share)	$ (0.35)	$ (0.35)
Weighted-average common shares outstanding - basic and diluted (in shares)	49,621,188	37,887,520

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		134 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013
Consolidated Statements of Comprehensive Loss
Net loss	$ (17,458)	$ (13,137)	$ (336,347)
Other comprehensive income:
Unrealized gain on available-for-sale securities	1	33	15
Other comprehensive income, before income taxes	1	33	15
Other comprehensive income	1	33	15
Comprehensive loss	$ (17,457)	$ (13,104)	$ (336,332)

- Definition

The change in equity [net assets] of a business enterprise during a period from transactions and other events and circumstances from non-owner sources which are attributable to the reporting entity. It includes all changes in equity during a period except those resulting from investments by owners and distributions to owners, but excludes any and all transactions which are directly or indirectly attributable to that ownership interest in subsidiary equity which is not attributable to the parent.

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- Definition

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

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Before tax amount of other comprehensive income (loss) attributable to the parent entity.

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Net of tax amount of other comprehensive income (loss) attributable to the parent entity.

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Net of tax amount of unrealized holding gain (loss) before reclassification adjustments and transfers on available-for-sale securities.

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Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		134 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013
Operating activities
Net loss	$ (17,458)	$ (13,137)	$ (336,347)
Adjustments to reconcile net loss to net cash used in operating activities:
Non-cash interest expense			525
Depreciation and amortization	439	420	12,207
Amortization of non-cash compensation			522
Stock-based compensation - employees	1,574	1,388	43,503
Stock-based compensation - non-employees			853
Stock-based license payments			1,220
Change in fair value of warrant liability	262	2,376	(1,291)
Loss on disposal of asset		27	388
Impairment of leasehold improvements			1,030
Non-cash charge for in-process research and development			418
Beneficial conversion feature related to bridge financing			135
Changes in operating assets and liabilities:
Receivable from GSK	1,917	742	(1,308)
Prepaid expenses and other current assets	517	3,114	(1,753)
Other non-current assets		267	(466)
Accounts payable and accrued expenses	(2,418)	(1,259)	6,427
Deferred reimbursements	1,267	(1,977)	31,685
Net cash used in operating activities	(13,900)	(8,039)	(242,252)
Investing activities
Sale and redemption of marketable securities	34,135	14,300	789,577
Purchases of marketable securities	(26,998)	(67,906)	(847,693)
Purchases of property and equipment	(372)	(3,082)	(18,585)
Net cash (used in)/provided by investing activities	6,765	(56,688)	(76,701)
Financing activities
Proceeds from the issuance of preferred stock, net of issuance costs			143,022
Proceeds from the issuance of common stock and warrants, net of issuance costs		62,063	193,441
Proceeds from the issuance of convertible notes			5,000
Payments of capital lease obligations			(5,587)
Payments of secured loan agreement	(100)	(313)	(4,156)
Proceeds from exercise of stock options		837	3,341
Proceeds from exercise of warrants (common and preferred)			264
Proceeds from capital asset financing arrangement			5,611
Proceeds from secured loan agreement		995	4,753
Net cash provided by/(used in) financing activities	(100)	63,582	345,689
Net (decrease)/increase in cash and cash equivalents	(7,235)	(1,145)	26,736
Cash and cash equivalents at beginning of period	33,971	25,668
Cash and cash equivalents at end of period	26,736	24,523	26,736
Supplemental disclosures of cash flow information
Cash paid during the period for interest	$ 7	$ 20	2,124
Non-cash activities
Conversion of warrants to common stock			386
Conversion of notes payable to Series B redeemable convertible preferred stock			5,000
Conversion of preferred stock to common stock			148,951
Accretion of redeemable convertible preferred stock			802
Beneficial conversion feature related to the issuance of Series C redeemable convertible preferred stock			$ 19,424

Description of Business and Significant Accounting Policies	3 Months Ended
	Mar. 31, 2013
Description of Business and Significant Accounting Policies
Description of Business and Significant Accounting Policies	Note 1. Description of Business and Significant Accounting Policies *Corporate Information, Status of Operations and Management Plans* Amicus Therapeutics, Inc. (the Company) was incorporated on February 4, 2002 in Delaware and is a biopharmaceutical company focused on the discovery, development and commercialization of next-generation medicines for a range of rare and orphan diseases, with a focus on improved therapies for lysosomal storage disorders (LSDs). The Company’s lead program is migalastat HCl for Fabry disease. Migalastat HCl is a novel, small molecule pharmacological chaperone in development as a monotherapy and in combination with enzyme replacement therapy (ERT) for Fabry disease. The Company is leveraging its Chaperone-Advanced Replacement Therapy, or (CHART tm) platform to develop next-generation therapies that combine pharmacological chaperones with enzyme therapies for Pompe, Gaucher and other LSDs. Current CHART programs for Pompe disease include the pharmacological chaperone AT2220 (duvoglustat HCl) co-administered with currently marketed Pompe ERTs (Myozyme®/Lumizyme®), as well as AT2220 co-formulated with a proprietary Pompe ERT. The Company’s activities since inception have consisted principally of raising capital, establishing facilities, and performing research and development. Accordingly, the Company is considered to be in the development stage. On July 17, 2012, the Company entered into an Amended and Restated License and Expanded Collaboration Agreement (the “Expanded Collaboration Agreement”) with an affiliate of GlaxoSmithKline PLC (GSK) pursuant to which the Company and GSK continue to develop and commercialize migalastat HCl for the treatment of Fabry disease. The Expanded Collaboration Agreement amends and replaces in its entirety the License and Collaboration Agreement entered into between the Company and GSK on October 28, 2010 (the “Original Collaboration Agreement”) for the development and commercialization of migalastat HCl. Under the terms of the Expanded Collaboration Agreement, the Company and GSK will co-develop all formulations of migalastat HCl for Fabry disease, including migalastat HCl monotherapy, currently in Phase 3 development, as well as migalastat HCl co-formulated with an investigational ERT for Fabry disease (the “Co-formulated Product”). The Co-formulated Product is being developed by the Company and GSK in collaboration with JCR Pharmaceutical Co., Ltd. The Company will commercialize all migalastat HCl products for Fabry disease in the United States while GSK will commercialize all such products in the rest of the world. The Company and GSK jointly fund development costs for all formulations of migalastat HCl in accordance with agreed upon development plans pursuant to which the Company and GSK fund 40% and 60% of such costs, respectively. Additionally, simultaneous with entry into the Expanded Collaboration Agreement, the Company and GSK entered into a Stock Purchase Agreement (the “SPA”) pursuant to which GSK purchased approximately 2.9 million shares of Amicus common stock at a price of $6.30 per share. The total value of this equity investment to the Company is approximately $18.6 million. As of March 31, 2013, GSK’s ownership position in the Company is 19.8%. For further information, see “— Note 7. Collaborative Agreements.” The Company had an accumulated deficit of approximately $336.3 million at March 31, 2013 and anticipates incurring losses through the year 2013 and beyond. The Company has not yet generated commercial sales revenue and has been able to fund its operating losses to date through the sale of its redeemable convertible preferred stock, issuance of convertible notes, net proceeds from its initial public offering (IPO) and subsequent stock offerings, payments from partners during the terms of the collaboration agreements and other financing arrangements. In March 2010, the Company sold 4.95 million shares of its common stock and warrants to purchase 1.9 million shares of common stock in a registered direct offering to a select group of institutional investors for net proceeds of $17.1 million. In October 2010, the Company sold 6.87 million shares of its common stock as part of the Original License and Collaboration Agreement with GSK for proceeds of $31 million. In March 2012, the Company sold 11.5 million shares of its common stock in a stock offering for net proceeds of $62.0 million. In July 2012, the Company sold 2.9 million shares of its common stock as part of the Expanded Collaboration Agreement with GSK for proceeds of $18.6 million. The Company believes that its existing cash and cash equivalents and short-term investments will be sufficient to cover its cash flow requirements for 2013. *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 Regulations S-X. Accordingly, they do not include all of the information and disclosures required by generally accepted accounting principles 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 year ended December 31, 2012. 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, 2012. *Revenue Recognition* The Company recognizes revenue when amounts are realized or realizable and earned. Revenue is considered realizable and earned when the following criteria are met: (1) persuasive evidence of an arrangement exists; (2) delivery has occurred or services have been rendered; (3) the price is fixed or determinable; and (4) collection of the amounts due are reasonably assured. In multiple element arrangements, revenue is allocated to each separate unit of accounting and each deliverable in an arrangement is evaluated to determine whether it represents separate units of accounting. A deliverable constitutes a separate unit of accounting when it has standalone value and there is no general right of return for the delivered elements. In instances when the aforementioned criteria are not met, the deliverable is combined with the undelivered elements and the allocation of the arrangement consideration and revenue recognition is determined for the combined unit as a single unit of accounting. Allocation of the consideration is determined at arrangement inception on the basis of each unit’s relative selling price. In instances where there is determined to be a single unit of accounting, the total consideration is applied as revenue for the single unit of accounting and is recognized over the period of inception through the date where the last deliverable within the single unit of accounting is expected to be delivered. The Company’s current revenue recognition policies, which were applied in fiscal 2010, provide that, when a collaboration arrangement contains multiple deliverables, such as license and research and development services, the Company allocates revenue to each separate unit of accounting based on a selling price hierarchy. The selling price hierarchy for a deliverable is based on (i) its vendor specific objective evidence (VSOE) if available, (ii) third party evidence (TPE) if VSOE is not available, or (iii) best estimated selling price (BESP) if neither VSOE nor TPE is available. The Company would establish the VSOE of selling price using the price charged for a deliverable when sold separately. The TPE of selling price would be established by evaluating largely similar and interchangeable competitor products or services in standalone sales to similarly situated customers. The BESP would be established considering internal factors such as an internal pricing analysis or an income approach using a discounted cash flow model. The Company also considers the impact of potential future payments it makes in its role as a vendor to its customers and evaluates if these potential future payments could be a reduction of revenue from that customer. If the potential future payments to the customer are: · a payment for an identifiable benefit; and · the identifiable benefit is separable from the existing relationship between the Company and its customer; and · the identifiable benefit can be obtained from a party other than the customer; and · the Company can reasonably estimate the fair value of the identifiable benefit then the payments are accounted for separate from the revenue received from that customer. If, however, all these criteria are not satisfied, then the payments are treated as a reduction of revenue from that customer. If the Company determines that any potential future payments to its customers are to be considered as a reduction of revenue, it must evaluate if the total amount of revenue to be received under the arrangement is fixed and determinable. If the total amount of revenue is not fixed and determinable due to the uncertain nature of the potential future payments to the customer, then any customer payments cannot be recognized as revenue until the total arrangement consideration becomes fixed and determinable. The reimbursements for research and development costs under collaboration agreements that meet the criteria for revenue recognition are included in Research Revenue and the costs associated with these reimbursable amounts are included in research and development expenses. In order to determine the revenue recognition for contingent milestones, the Company evaluates the contingent milestones using the criteria as provided by the Financial Accounting Standards Boards (FASB) guidance on the milestone method of revenue recognition at the inception of a collaboration agreement. The criteria requires that (i) the Company determines if the milestone is commensurate with either its performance to achieve the milestone or the enhancement of value resulting from the Company’s activities to achieve the milestone, (ii) the milestone be related to past performance, and (iii) the milestone be reasonable relative to all deliverable and payment terms of the collaboration arrangement. If these criteria are met then the contingent milestones can be considered as substantive milestones and will be recognized as revenue in the period that the milestone is achieved. *Fair Value Measurements* The Company records certain asset and liability balances under the fair value measurements as defined by the FASB guidance. Current FASB fair value guidance emphasizes that fair value is a market-based measurement, not an entity-specific measurement. Therefore, a fair value measurement should be determined based on the assumptions that market participants would use in pricing the asset or liability. As a basis for considering market participant assumptions in fair value measurements, current FASB guidance establishes a fair value hierarchy that distinguishes between market participant assumptions based on market data obtained from sources independent of the reporting entity (observable inputs that are classified within Levels 1 and 2 of the hierarchy) and the reporting entity’s own assumptions that market participants assumptions would use in pricing assets or liabilities (unobservable inputs classified within Level 3 of the hierarchy). Level 1 inputs utilize quoted prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access at measurement date. Level 2 inputs are inputs other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly. Level 2 inputs may include quoted prices for similar assets and liabilities in active markets, as well as inputs that are observable for the asset or liability (other than quoted prices), such as interest rates, foreign exchange rates, and yield curves that are observable at commonly quoted intervals. Level 3 inputs are unobservable inputs for the asset or liability, which is typically based on an entity’s own assumptions, as there is little, if any, related market activity. In instances where the determination of the fair value measurement is based on inputs from different levels of the fair value hierarchy, the level in the fair value hierarchy within which the entire fair value measurement falls is based on the lowest level input that is significant to the fair value measurement in its entirety. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment, and considers factors specific to the asset or liability. *New Accounting Standards* In February 2013, the FASB amended its guidance to require an entity to present the effect of certain significant reclassifications out of accumulated other comprehensive income on the respective line items in net income. The new accounting guidance does not change the items that must be reported in other comprehensive income or when an item of other comprehensive income must be reclassified to net income. The guidance is effective prospectively for fiscal years beginning after December 15, 2012. The Company adopted these new provisions for the quarter beginning January 1, 2013. As the guidance requires additional presentation only, there was no impact to the Company’s consolidated results of operations or financial position.

- Definition

The entire disclosure for the organization, consolidation and basis of presentation of financial statements disclosure, and significant accounting policies of the reporting entity. May be provided in more than one note to the financial statements, as long as users are provided with an understanding of (1) the significant judgments and assumptions made by an enterprise in determining whether it must consolidate a VIE and/or disclose information about its involvement with a VIE, (2) the nature of restrictions on a consolidated VIE's assets reported by an enterprise in its statement of financial position, including the carrying amounts of such assets, (3) the nature of, and changes in, the risks associated with an enterprise's involvement with the VIE, and (4) how an enterprise's involvement with the VIE affects the enterprise's financial position, financial performance, and cash flows. Describes procedure if disclosures are provided in more than one note to the financial statements.

+ References + Details

Cash, Money Market Funds and Marketable Securities

3 Months Ended

Mar. 31, 2013

Cash, Money Market Funds and Marketable Securities

Cash, Money Market Funds and Marketable Securities

Note 2. Cash, Money Market Funds and Marketable Securities

As of March 31, 2013, the Company held $26.7 million in cash and cash equivalents and $58.0 million of available-for-sale investment securities which are reported at fair value on the Company’s balance sheet. Unrealized holding gains and losses are reported within comprehensive income/(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. To date, only temporary impairment adjustments have been recorded.

Consistent with the Company’s investment policy, the Company does not use derivative financial instruments in its investment portfolio. 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.

Cash and available-for-sale securities consisted of the following as of December 31, 2012 and March 31, 2013 (in thousands):

	As of December 31, 2012
	Cost		Unrealized Gain		Unrealized Loss			Fair Value
Cash balances	$	33,971	$	—	$	—		$	33,971
Corporate debt securities	42,503		5		(11		)	42,497
Commercial paper	19,725		19		—			19,744
Certificate of deposit	2,909		1		—			2,910
	$	99,108	$	25	$	(11	)	$	99,122

Included in cash and cash equivalents	$	33,971	$	—	$	—		$	33,971
Included in marketable securities	65,137		25		(11		)	65,151
Total cash and available for sale securities	$	99,108	$	25	$	(11	)	$	99,122

	As of March 31, 2013
	Cost		Unrealized Gain		Unrealized Loss			Fair Value
Cash balances	$	26,736	$	—	$	—		$	26,736
Corporate debt securities	35,934		3		(13		)	35,924
Commercial paper	21,716		25		—			21,741
Certificate of deposit	350		—		—			350
	$	84,736	$	28	$	(13	)	$	84,751

Included in cash and cash equivalents	$	26,736	$	—	$	—		$	26,736
Included in marketable securities	58,000		28		(13		)	58,015
Total cash and available for sale securities	$	84,736	$	28	$	(13	)	$	84,751

Unrealized gains and losses are reported as a component of other comprehensive income/(loss) in the statements of comprehensive loss. For the year ended December 31, 2012, and the three months ended March 31, 2013, unrealized holding gains of $10 thousand and $1 thousand were included in the statements of comprehensive loss, respectively.

For the year ended December 31, 2012 and the three months ended March 31, 2013, there were no realized gains or losses. The cost of securities sold is based on the specific identification method.

Unrealized loss positions in the available for sale securities as of December 31, 2012 and March 31, 2013 reflect temporary impairments that have not been recognized and have been in a loss position for less than twelve months. The fair value of these available for sale securities in unrealized loss positions was $33.1 million and $26.1 million as of December 31, 2012 and March 31, 2013, respectively.

The Company holds available-for-sale investment securities which are reported at fair value on the Company’s balance sheet. Unrealized holding gains and losses are reported within accumulated other comprehensive income (“AOCI”) in the statements of comprehensive loss. The changes in AOCI associated with the unrealized holding gain on available-for-sale investments during the three months ended March 31, 2012 and 2013, were as follows (in thousands):

	Three Months Ended March 31,
	2012		2013
Balance, beginning	$	4	$	14
Current period changes in fair value, (a)	33		1
Reclassification of earnings, (a)	—		—
Balance, ending	$	37	$	15

(a) — Taxes have not been accrued on the unrealized gain on securities as the Company is in a loss position for all periods presented.

Stockholders' Equity

3 Months Ended

Mar. 31, 2013

Stockholders' Equity

Stockholders' Equity

Note 4. Stockholders’ Equity

Common Stock and Warrants

As of March 31, 2013, the Company was authorized to issue 125,000,000 shares of common stock. Dividends on common stock will be paid when, and if declared by the board of directors. Each holder of common stock is entitled to vote on all matters and is entitled to one vote for each share held.

In July 2012, Amicus and GSK entered into the SPA pursuant to which GSK purchased 2.9 million unregistered shares of Amicus common stock at a price of $6.30 per share. The total purchase price for these shares was $18.6 million. The Company received all proceeds from the sale of such shares on July 26, 2012. As of March 31, 2013 GSK had a 19.8% ownership position in the Company.

In March 2012, the Company sold 11.5 million shares of its common stock at a public offering price of $5.70 through a Registration Statement on Form S-3 that was declared effective by the SEC on May 27, 2009. The aggregate offering proceeds were $65.6 million.

In October 2010, GSK purchased approximately 6.9 million shares of the Company’s common stock at $4.56 per share, in connection with the Original Collaboration Agreement. The total value of this equity investment was approximately $31 million.

In March 2010, the Company sold 4.9 million shares of its common stock and warrants to purchase 1.9 million shares of common stock in a registered direct offering to a selected group of institutional investors through a Registration Statement on Form S-3 that was declared effective by the SEC on May 27, 2009. The shares of common stock and warrants were sold in units consisting of one share of common stock and one warrant to purchase 0.375 shares of common stock at a price of $3.74 per unit. The warrants have a term of four years and are exercisable any time on or after the six month anniversary of the date they were issued, at an exercise price of $4.43 per share. The gross offering proceeds were $18.5 million. There were approximately 1.4 million warrants outstanding at March 31, 2013.

Stock Option Plans

During the three months ended March 31, 2013, the Company recorded stock-based compensation expense of approximately $1.6 million. The stock-based compensation expense had no impact on the Company’s cash flows from operations and financing activities. As of March 31, 2013, the total unrecognized compensation cost related to non-vested stock options granted was $11.3 million and is expected to be recognized over a weighted average period of 2.6 years. The following table summarizes information related to stock compensation expense recognized in the statements of operations (in thousands):

	Three Months Ended March 31,
	2012		2013
Stock compensation expense recognized in:
Research and development expense	$	873	$	924
General and administrative expense	515		650
Total stock compensation expense	$	1,388	$	1,574

The fair value of the 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 March 31,
	2012			2013
Expected stock price volatility	78.4		%	82.0		%
Risk free interest rate	1.1		%	1.2		%
Expected life of options (years)	6.25			6.25
Expected annual dividend per share	$	0.00		$	0.00

A summary of option activities related to the Company’s stock options for the three months ended March 31, 2013 is as follows:

					Weighted
			Weighted		Average
	Number		Average		Remaining	Aggregate
	of		Exercise		Contractual	Intrinsic
	Shares		Price		Life	Value
	(in thousands)					(in thousands)

Balance at December 31, 2012	7,974.2		$	6.35
Options granted	1,154.5		$	3.53
Options exercised	—		$	—
Options forfeited	(47.6	)	$	4.94
Balance at March 31, 2013	9,081.1		$	5.99	7.51 years	$	207
Vested and unvested expected to vest, March 31, 2013	8,012.5		$	6.10	7.3 years	$	132
Exercisable at March 31, 2013	4,450.9		$	7.25	6.0 years	$	166

- Definition

The entire disclosure for shareholders' equity, comprised of portions attributable to the parent entity and noncontrolling interest, if any, including other comprehensive income (as applicable). Including, but not limited to: (1) balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings; (2) accumulated balance for each classification of other comprehensive income and total amount of comprehensive income; (3) amount and nature of changes in separate accounts, including the number of shares authorized and outstanding, number of shares issued upon exercise and conversion, and for other comprehensive income, the adjustments for reclassifications to net income; (4) rights and privileges of each class of stock authorized; (5) basis of treasury stock, if other than cost, and amounts paid and accounting treatment for treasury stock purchased significantly in excess of market; (6) dividends paid or payable per share and in the aggregate for each class of stock for each period presented; (7) dividend restrictions and accumulated preferred dividends in arrears (in aggregate and per share amount); (8) retained earnings appropriations or restrictions, such as dividend restrictions; (9) impact of change in accounting principle, initial adoption of new accounting principle and correction of an error in previously issued financial statements; (10) shares held in trust for Employee Stock Ownership Plan (ESOP); (11) deferred compensation related to issuance of capital stock; (12) note received for issuance of stock; (13) unamortized discount on shares; (14) description, terms, and number of warrants or rights outstanding; (15) shares under subscription and subscription receivables, effective date of new retained earnings after quasi-reorganization and deficit eliminated by quasi-reorganization and, for a period of at least ten years after the effective date, the point in time from which the new retained dates; and (16) retroactive effective of subsequent change in capital structure.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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-Paragraph 1
-Subparagraph (SX 210.4-08.(d),(e))
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Reference 6: http://www.xbrl.org/2003/role/presentationRef
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Reference 7: http://www.xbrl.org/2003/role/presentationRef
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Reference 8: http://www.xbrl.org/2003/role/presentationRef
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-URI http://asc.fasb.org/extlink&oid=6959260&loc=d3e187085-122770

Reference 9: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=6405834&loc=d3e23285-112656

Reference 10: http://www.xbrl.org/2003/role/presentationRef
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Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Preferred Stock
-URI http://asc.fasb.org/extlink&oid=6521494

Reference 12: http://www.xbrl.org/2003/role/presentationRef
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Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Research Bulletin (ARB)
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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 15: http://www.xbrl.org/2003/role/presentationRef
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Reference 16: http://www.xbrl.org/2003/role/presentationRef
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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 17: http://www.xbrl.org/2003/role/presentationRef
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Reference 18: http://www.xbrl.org/2003/role/presentationRef
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Reference 19: http://www.xbrl.org/2003/role/presentationRef
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Reference 20: http://www.xbrl.org/2003/role/presentationRef
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-Name Regulation S-X (SX)
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Reference 21: http://www.xbrl.org/2003/role/presentationRef
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Reference 22: http://www.xbrl.org/2003/role/presentationRef
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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 23: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Article 3

+ Details

Assets and Liabilities Measured at Fair Value

3 Months Ended

Mar. 31, 2013

Assets and Liabilities Measured at Fair Value

Assets and Liabilities Measured at Fair Value

Note 6. 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.

Cash, Money Market Funds and Marketable Securities

The Company classifies its cash and money market funds within the fair value hierarchy as Level 1 as these assets are valued using quoted prices in active market for identical assets at the measurement date. The Company considers its investments in marketable securities as available-for-sale and classifies these assets 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 three months ended March 31, 2013. No transfers of assets between Level 1 and Level 2 of the fair value measurement hierarchy occurred during the three months ended March 31, 2013.

Secured Debt

As disclosed in Note 5, the Company has a loan and security agreement with Silicon Valley Bank. The carrying amount of the Company’s borrowings approximates fair value at March 31, 2013. The Company’s secured debt is classified as Level 2 and the fair value is estimated 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.

Warrants

The Company allocated $3.3 million of proceeds from its March 2010 registered direct offering to warrants issued in connection with the offering that was classified as a liability. The valuation of the warrants is determined using the Black-Scholes model. This model uses inputs such as the underlying price of the shares issued when the warrant is exercised, volatility, risk free interest rate and expected life of the instrument. The Company has determined that the warrant liability should be classified within Level 3 of the fair value hierarchy by evaluating each input for the Black-Scholes model against the fair value hierarchy criteria and using the lowest level of input as the basis for the fair value classification. There are six inputs: closing price of Amicus stock on the day of evaluation; the exercise price of the warrants; the remaining term of the warrants; the volatility of Amicus’ stock over that term; annual rate of dividends; and the riskless rate of return. Of those inputs, the exercise price of the warrants and the remaining term are readily observable in the warrant agreements. The annual rate of dividends is based on the Company’s historical practice of not granting dividends. The closing price of Amicus stock would fall under Level 1 of the fair value hierarchy as it is a quoted price in an active market. The riskless rate of return is a Level 2 input, while the historical volatility is a Level 3 input in accordance with the fair value accounting guidance. Since the lowest level input is a Level 3, the Company determined the warrant liability is most appropriately classified within Level 3 of the fair value hierarchy. This liability is subject to fair value mark-to-market adjustment each period and approximately 0.5 million warrants were exercised in 2012. The Company recognized the change in the fair value of the warrant liability as non-operating expense of $0.3 million for the three months ended March 31, 2013 and the resulting fair value of the warrant liability at March 31, 2013 was $1.2 million. The weighted average assumptions used in the Black-Scholes valuation model for the warrants are as follows:

	Three Months Ended March 31,
	2012			2013
Expected stock price volatility	72.6		%	98.8		%
Risk free interest rate	0.31		%	0.13		%
Expected life of warrants (years)	1.92			0.92
Expected annual dividend per share	$	0.00		$	0.00

A summary of the fair value of the Company’s assets and liabilities aggregated by the level in the fair value hierarchy within which those measurements fall as of December 31, 2012, are identified in the following table (in thousands):

	Level 1		Level 2		Total
*Assets:*
Cash/Money market funds	$	33,971	$	—	$	33,971
Corporate debt securities	—		42,497		42,497
Commercial paper	—		19,744		19,744
Certificate of deposit	—		2,910		2,910
	$	33,971	$	65,151	$	99,122

	Level 1		Level 2		Level 3		Total
*Liabilities:*
Secured debt	$	—	$	697	$	—	$	697
Warrants liability	—		—		908		908
	$	—	$	697	$	908	$	1,605

A summary of the fair value of the Company’s assets and liabilities aggregated by the level in the fair value hierarchy within which those measurements fall as of March 31, 2013, are identified in the following table (in thousands):

	Level 1		Level 2		Total
*Assets:*
Cash/Money market funds	$	26,736	$	—	$	26,736
Corporate debt securities	—		35,924		35,924
Commercial paper	—		21,741		21,741
Certificate of deposit	—		350		350
	$	26,736	$	58,015	$	84,751

	Level 1		Level 2		Level 3		Total
*Liabilities:*
Secured debt	$	—	$	597	$	—	$	597
Warrants liability	—		—		1,170		1,170
	$	—	$	597	$	1,170	$	1,767

The change in the fair value of the Level 3 liability was an increase of $2.4 million and $0.3 million for the three months ended March 31, 2012, and 2013 respectively.

- 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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 44A, 44B
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 159
-Paragraph 17-22, 27, 28
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 15A
-Subparagraph a-d
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 15C, 15D
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 157
-Paragraph 32, 33, 34
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 3, 10, 14, 15
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Collaborative Agreements	3 Months Ended
Collaborative Agreements	Mar. 31, 2013
Collaborative Agreements
Collaborative Agreements	Note 7. Collaborative Agreements GSK On October 28, 2010, the Company entered into the Original Collaboration Agreement with Glaxo Group Limited, an affiliate of GSK, to develop and commercialize migalastat HCl. Under the terms of the Original Collaboration Agreement, GSK received an exclusive worldwide license to develop, manufacture and commercialize migalastat HCl. In consideration of the license grant, the Company received an upfront, license payment of $30 million from GSK and was eligible to receive further payments of approximately $173.5 million upon the successful achievement of development, regulatory and commercialization milestones, as well as tiered double-digit royalties on global sales of migalastat HCl. Potential payments included up to (i) $13.5 million related to the attainment of certain clinical development objectives and the acceptance of regulatory filings in select worldwide markets, (ii) $80 million related to market approvals for migalastat HCl in selected territories throughout the world, and (iii) $80 million associated with the achievement of certain sales thresholds. GSK and the Company were jointly funding development costs in accordance with an agreed upon development plan. Additionally, GSK purchased approximately 6.9 million shares of the Company’s common stock at $4.56 per share, a 30% premium on the average price per share of the Company’s stock over a 60 day period preceding the closing date of the transaction. The total value of this equity investment to the Company was approximately $31 million. On July 17, 2012, the Company entered into the Expanded Collaboration Agreement with GSK pursuant to which the Company and GSK continue to develop and commercialize migalastat HCl, currently in Phase 3 development for the treatment of Fabry disease. The Expanded Collaboration Agreement amends and replaces in its entirety the Original Collaboration Agreement. Under the terms of the Expanded Collaboration Agreement, the Company and GSK will co-develop all formulations of migalastat HCl for Fabry disease, including the development of migalastat HCl co-formulated with an investigational ERT for Fabry disease in collaboration with another GSK collaborator JCR Pharmaceutical Co., Ltd. The Company will commercialize all migalastat HCl products for Fabry disease in the United States while GSK will commercialize all such products in the rest of the world. The exclusive license granted to GSK under the Original Collaboration Agreement to commercialize migalastat HCl worldwide was replaced under the Expanded Collaboration Agreement, which grants two exclusive licenses: (i) an exclusive license from GSK to the Company to commercialize migalastat HCl in the United States, and (ii) an exclusive license from the Company to GSK to commercialize migalastat HCl in the rest of world. Amicus and GSK each have a license to manufacture migalastat HCl for commercialization of monotherapy and chaperone-ERT co-administration migalastat HCl products while GSK maintains an exclusive license to manufacture such products for development purposes (subject to limited exceptions) and to manufacture the Co-formulated Product. In the event of a change of control in the Company during the term of the Expanded Collaboration Agreement, GSK has the option to purchase an exclusive license to develop, manufacture and commercialize migalastat HCl in the United States. GSK is eligible to receive U.S. regulatory approval milestones totaling $20 million for migalastat HCl monotherapy and migalastat HCl-ERT co-administration, and additional regulatory approval and product launch milestone payments totaling up to $35 million within seven years following the launch of the Co-formulated Product. The Company will also be responsible for certain pass-through milestone payments and single-digit royalties on the net U.S. sales of the Co-formulated Product that GSK must pay to a third party. In addition, the Company is no longer eligible to receive any milestones or royalties it would have been eligible to receive under the Original Collaboration Agreement other than a $3.5 million clinical development milestone achieved in the second quarter of 2012 and paid by GSK to Amicus in the third quarter of 2012. The Company and GSK will continue to jointly fund development costs for all formulations of migalastat HCl in accordance with agreed upon development plans pursuant to which the Company and GSK funded 25% and 75% of such costs, respectively, for the monotherapy and co-administration programs during 2012 and 40% and 60%, respectively, in 2013 and beyond. Effective upon entry into the Expanded Collaboration Agreement, costs for the development of the Co-formulated Product are also funded 40% and 60% between Amicus and GSK, respectively. Additionally, simultaneous with entry into the Expanded Collaboration Agreement, Amicus and GSK entered into an SPA pursuant to which GSK purchased approximately 2.9 million shares of Amicus common stock at a price of $6.30 per share. The SPA provides GSK with customary registration rights for the shares purchased and includes a six-month lock-up provision. The total purchase price was $18.6 million and the Company received all proceeds from the sale of such shares on July 26, 2012. As of March 31, 2013, GSK had a 19.8% ownership position in the Company as a result of the Original and Expanded Collaboration Agreements. Under the Original Collaboration Agreement, the upfront license fee, together with the premium received on the stock purchase, was being recognized as Collaboration Revenue over the original development period. In addition, the Company was receiving reimbursements of research expenditures under the cost sharing arrangement which was being accounted for as research revenue on the statement of operations. Under the Expanded Collaboration Agreement, the Company will continue to receive research expense reimbursements for the development of migalastat HCl but may be required to pay contingent milestones to GSK in the future related to the US commercial rights to migalastat HCl. In accordance with the revenue recognition guidance related to multiple-element arrangements, the Company identified all of the deliverables at the inception of the Expanded Collaboration Agreement. The significant deliverables were determined to be the rest of world licensing rights to migalastat HCl, the research services to continue and complete the development of migalastat HCl and the delivery of the Company’s common stock. The Company determined that the rest of world licensing rights and the research services represent one unit of accounting as none of these deliverables on its own has standalone value separate from the other. The Company also determined that the delivery of the Company’s common stock does have standalone value separate from the rest of world licensing rights and the research services. As a result, the Company’s common stock was considered a separate unit of accounting and was accounted for as an issuance of common stock. However, as the Company’s common stock was sold at a premium to the market closing price, the premium amount paid over the market closing price was determined to be additional consideration paid to the Company for the collaboration agreement and was included as consideration for the single unit of accounting (rest of world licensing rights and research services) identified above. In evaluating the impact of the Expanded Collaboration Agreement, the Company applied the accounting guidance regarding the impact of potential future payments it may make in its role as a vendor (Amicus) to its customer (GSK) and evaluated if these potential future payments could be a reduction of revenue from GSK. If the potential future payments to GSK are: · a payment for an identifiable benefit, and · the identifiable benefit is separable from the existing relationship between the Company and GSK, and · the identifiable benefit can be obtained from a party other than GSK, and · the Company can reasonably estimate the fair value of the identifiable benefit, then the potential future payments would be treated separately from the collaboration and research revenue. However, if all these criteria are not satisfied, then the potential future payments are treated as a reduction of revenue. Accordingly, the Company does not believe that, for accounting purposes, the new US licensing rights to migalastat HCl obtained from GSK represent a separate, identifiable benefit from the licenses in the Original Collaboration Agreement. The contingent amounts payable to GSK are not sufficiently separable from GSK’s original license and the research and development reimbursements such that Amicus could not have entered into a similar exchange transaction with another party. Additionally, the Company cannot reasonably estimate the fair value of the US licensing rights to migalastat HCl. The Company determined that the potential future payments to GSK would be treated as a reduction of revenue and that the total amount of revenue to be received under the arrangement is no longer fixed or determinable as the contingent milestone payments are subject to significant uncertainty. As a result, the Company no longer recognizes any of the upfront license fee and premium on the equity purchase from GSK until such time as the arrangement consideration becomes fixed or determinable, because an indeterminable amount may ultimately be payable back to GSK. These amounts (the balance of the unrecognized upfront license fee and the premium on the equity purchases) are classified as deferred reimbursements on the balance sheet. The recognition of Research Revenue is also affected by the determination that the overall total arrangement consideration is no longer fixed and determinable, despite the fact that the research activities will continue and that the research expense reimbursements by GSK to Amicus will be received as the research activities related to the reimbursement would have already been completed. Therefore any research reimbursements from GSK are recorded as deferred reimbursements on the balance sheet and not recognized until the total arrangement consideration becomes fixed and determinable. As a result, all revenue recognition was suspended until the total arrangement consideration becomes fixed and determinable. In addition, future milestone payments made by the Company will be applied against the balance of this deferred reimbursements account. Revenue recognition for research expense reimbursements, the original upfront license fee, and the equity premiums will resume once the total arrangement consideration becomes fixed and determinable which will occur when the balance of the deferred reimbursements account is sufficient to cover all the remaining contingent milestone payments. Under the Original Collaboration Agreement, the Company evaluated the contingent milestones and determined that they were substantive milestones and would be recognized as revenue in the period that the milestone is achieved. The Company determined that the research based milestones were commensurate with the enhanced value of each delivered item as a result of the Company’s specific performance to achieve the milestones. The research based milestones would have related to past performances when achieved and were reasonable relative to the other payment terms within the Original Collaboration Agreement. In June 2012, the Company achieved a clinical development milestone and recognized $3.5 million of milestone revenue. Under the terms of the Expanded Collaboration Agreement, the Company is no longer entitled to receive any milestone payments from GSK.

Description of Business and Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2013
Description of Business and Significant Accounting Policies
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 Regulations S-X. Accordingly, they do not include all of the information and disclosures required by generally accepted accounting principles 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 year ended December 31, 2012. 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, 2012.
Revenue Recognition	*Revenue Recognition* The Company recognizes revenue when amounts are realized or realizable and earned. Revenue is considered realizable and earned when the following criteria are met: (1) persuasive evidence of an arrangement exists; (2) delivery has occurred or services have been rendered; (3) the price is fixed or determinable; and (4) collection of the amounts due are reasonably assured. In multiple element arrangements, revenue is allocated to each separate unit of accounting and each deliverable in an arrangement is evaluated to determine whether it represents separate units of accounting. A deliverable constitutes a separate unit of accounting when it has standalone value and there is no general right of return for the delivered elements. In instances when the aforementioned criteria are not met, the deliverable is combined with the undelivered elements and the allocation of the arrangement consideration and revenue recognition is determined for the combined unit as a single unit of accounting. Allocation of the consideration is determined at arrangement inception on the basis of each unit’s relative selling price. In instances where there is determined to be a single unit of accounting, the total consideration is applied as revenue for the single unit of accounting and is recognized over the period of inception through the date where the last deliverable within the single unit of accounting is expected to be delivered. The Company’s current revenue recognition policies, which were applied in fiscal 2010, provide that, when a collaboration arrangement contains multiple deliverables, such as license and research and development services, the Company allocates revenue to each separate unit of accounting based on a selling price hierarchy. The selling price hierarchy for a deliverable is based on (i) its vendor specific objective evidence (VSOE) if available, (ii) third party evidence (TPE) if VSOE is not available, or (iii) best estimated selling price (BESP) if neither VSOE nor TPE is available. The Company would establish the VSOE of selling price using the price charged for a deliverable when sold separately. The TPE of selling price would be established by evaluating largely similar and interchangeable competitor products or services in standalone sales to similarly situated customers. The BESP would be established considering internal factors such as an internal pricing analysis or an income approach using a discounted cash flow model. The Company also considers the impact of potential future payments it makes in its role as a vendor to its customers and evaluates if these potential future payments could be a reduction of revenue from that customer. If the potential future payments to the customer are: · a payment for an identifiable benefit; and · the identifiable benefit is separable from the existing relationship between the Company and its customer; and · the identifiable benefit can be obtained from a party other than the customer; and · the Company can reasonably estimate the fair value of the identifiable benefit then the payments are accounted for separate from the revenue received from that customer. If, however, all these criteria are not satisfied, then the payments are treated as a reduction of revenue from that customer. If the Company determines that any potential future payments to its customers are to be considered as a reduction of revenue, it must evaluate if the total amount of revenue to be received under the arrangement is fixed and determinable. If the total amount of revenue is not fixed and determinable due to the uncertain nature of the potential future payments to the customer, then any customer payments cannot be recognized as revenue until the total arrangement consideration becomes fixed and determinable. The reimbursements for research and development costs under collaboration agreements that meet the criteria for revenue recognition are included in Research Revenue and the costs associated with these reimbursable amounts are included in research and development expenses. In order to determine the revenue recognition for contingent milestones, the Company evaluates the contingent milestones using the criteria as provided by the Financial Accounting Standards Boards (FASB) guidance on the milestone method of revenue recognition at the inception of a collaboration agreement. The criteria requires that (i) the Company determines if the milestone is commensurate with either its performance to achieve the milestone or the enhancement of value resulting from the Company’s activities to achieve the milestone, (ii) the milestone be related to past performance, and (iii) the milestone be reasonable relative to all deliverable and payment terms of the collaboration arrangement. If these criteria are met then the contingent milestones can be considered as substantive milestones and will be recognized as revenue in the period that the milestone is achieved.
Fair Value Measurements	*Fair Value Measurements* The Company records certain asset and liability balances under the fair value measurements as defined by the FASB guidance. Current FASB fair value guidance emphasizes that fair value is a market-based measurement, not an entity-specific measurement. Therefore, a fair value measurement should be determined based on the assumptions that market participants would use in pricing the asset or liability. As a basis for considering market participant assumptions in fair value measurements, current FASB guidance establishes a fair value hierarchy that distinguishes between market participant assumptions based on market data obtained from sources independent of the reporting entity (observable inputs that are classified within Levels 1 and 2 of the hierarchy) and the reporting entity’s own assumptions that market participants assumptions would use in pricing assets or liabilities (unobservable inputs classified within Level 3 of the hierarchy). Level 1 inputs utilize quoted prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access at measurement date. Level 2 inputs are inputs other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly. Level 2 inputs may include quoted prices for similar assets and liabilities in active markets, as well as inputs that are observable for the asset or liability (other than quoted prices), such as interest rates, foreign exchange rates, and yield curves that are observable at commonly quoted intervals. Level 3 inputs are unobservable inputs for the asset or liability, which is typically based on an entity’s own assumptions, as there is little, if any, related market activity. In instances where the determination of the fair value measurement is based on inputs from different levels of the fair value hierarchy, the level in the fair value hierarchy within which the entire fair value measurement falls is based on the lowest level input that is significant to the fair value measurement in its entirety. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment, and considers factors specific to the asset or liability.
New Accounting Standards	*New Accounting Standards* In February 2013, the FASB amended its guidance to require an entity to present the effect of certain significant reclassifications out of accumulated other comprehensive income on the respective line items in net income. The new accounting guidance does not change the items that must be reported in other comprehensive income or when an item of other comprehensive income must be reclassified to net income. The guidance is effective prospectively for fiscal years beginning after December 15, 2012. The Company adopted these new provisions for the quarter beginning January 1, 2013. As the guidance requires additional presentation only, there was no impact to the Company’s consolidated results of operations or financial position.

- Definition

Disclosure of accounting policy for revenue recognition. If the entity has different policies for different types of revenue transactions, the policy for each material type of transaction is generally disclosed. If a sales transaction has multiple element arrangements (for example, delivery of multiple products, services or the rights to use assets) the disclosure may indicate the accounting policy for each unit of accounting as well as how units of accounting are determined and valued. The disclosure may encompass important judgment as to appropriateness of principles related to recognition of revenue. The disclosure also may indicate the entity's treatment of any unearned or deferred revenue that arises from the transaction.

+ References + Details

Cash, Money Market Funds and Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2013

Cash, Money Market Funds and Marketable Securities

Schedule of cash and available for sale securities

Cash and available-for-sale securities consisted of the following as of December 31, 2012 and March 31, 2013 (in thousands):

	As of December 31, 2012
	Cost		Unrealized Gain		Unrealized Loss			Fair Value
Cash balances	$	33,971	$	—	$	—		$	33,971
Corporate debt securities	42,503		5		(11		)	42,497
Commercial paper	19,725		19		—			19,744
Certificate of deposit	2,909		1		—			2,910
	$	99,108	$	25	$	(11	)	$	99,122

Included in cash and cash equivalents	$	33,971	$	—	$	—		$	33,971
Included in marketable securities	65,137		25		(11		)	65,151
Total cash and available for sale securities	$	99,108	$	25	$	(11	)	$	99,122

	As of March 31, 2013
	Cost		Unrealized Gain		Unrealized Loss			Fair Value
Cash balances	$	26,736	$	—	$	—		$	26,736
Corporate debt securities	35,934		3		(13		)	35,924
Commercial paper	21,716		25		—			21,741
Certificate of deposit	350		—		—			350
	$	84,736	$	28	$	(13	)	$	84,751

Included in cash and cash equivalents	$	26,736	$	—	$	—		$	26,736
Included in marketable securities	58,000		28		(13		)	58,015
Total cash and available for sale securities	$	84,736	$	28	$	(13	)	$	84,751

Schedule of changes in AOCI associated with the unrealized holding gain on available-for-sale investments

The changes in AOCI associated with the unrealized holding gain on available-for-sale investments during the three months ended March 31, 2012 and 2013, were as follows (in thousands):

	Three Months Ended March 31,
	2012		2013
Balance, beginning	$	4	$	14
Current period changes in fair value, (a)	33		1
Reclassification of earnings, (a)	—		—
Balance, ending	$	37	$	15

(a) — Taxes have not been accrued on the unrealized gain on securities as the Company is in a loss position for all periods presented.

Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2013

Stockholders' Equity

Summary of information related to stock compensation expense recognized in the statements of operations

The following table summarizes information related to stock compensation expense recognized in the statements of operations (in thousands):

	Three Months Ended March 31,
	2012		2013
Stock compensation expense recognized in:
Research and development expense	$	873	$	924
General and administrative expense	515		650
Total stock compensation expense	$	1,388	$	1,574

Schedule of fair value weighted-average assumptions

	Three Months Ended March 31,
	2012			2013
Expected stock price volatility	78.4		%	82.0		%
Risk free interest rate	1.1		%	1.2		%
Expected life of options (years)	6.25			6.25
Expected annual dividend per share	$	0.00		$	0.00

Summary of option activities

					Weighted
			Weighted		Average
	Number		Average		Remaining	Aggregate
	of		Exercise		Contractual	Intrinsic
	Shares		Price		Life	Value
	(in thousands)					(in thousands)

Balance at December 31, 2012	7,974.2		$	6.35
Options granted	1,154.5		$	3.53
Options exercised	—		$	—
Options forfeited	(47.6	)	$	4.94
Balance at March 31, 2013	9,081.1		$	5.99	7.51 years	$	207
Vested and unvested expected to vest, March 31, 2013	8,012.5		$	6.10	7.3 years	$	132
Exercisable at March 31, 2013	4,450.9		$	7.25	6.0 years	$	166

- Definition

Tabular disclosure of the allocation of equity-based compensation costs to a given line item on the balance sheet and income statement for the period. This may include the reporting line for the costs and the amount capitalized and expensed.

+ References + Details

Assets and Liabilities Measured at Fair Value (Tables)

3 Months Ended

Mar. 31, 2013

Assets and Liabilities Measured at Fair Value

Schedule of weighted average assumptions used in the Black-Scholes valuation model for the warrants

	Three Months Ended March 31,
	2012			2013
Expected stock price volatility	72.6		%	98.8		%
Risk free interest rate	0.31		%	0.13		%
Expected life of warrants (years)	1.92			0.92
Expected annual dividend per share	$	0.00		$	0.00

Schedule of financial assets and liabilities subject to fair value measurements

	Level 1		Level 2		Total
*Assets:*
Cash/Money market funds	$	33,971	$	—	$	33,971
Corporate debt securities	—		42,497		42,497
Commercial paper	—		19,744		19,744
Certificate of deposit	—		2,910		2,910
	$	33,971	$	65,151	$	99,122

	Level 1		Level 2		Level 3		Total
*Liabilities:*
Secured debt	$	—	$	697	$	—	$	697
Warrants liability	—		—		908		908
	$	—	$	697	$	908	$	1,605

	Level 1		Level 2		Total
*Assets:*
Cash/Money market funds	$	26,736	$	—	$	26,736
Corporate debt securities	—		35,924		35,924
Commercial paper	—		21,741		21,741
Certificate of deposit	—		350		350
	$	26,736	$	58,015	$	84,751

	Level 1		Level 2		Level 3		Total
*Liabilities:*
Secured debt	$	—	$	597	$	—	$	597
Warrants liability	—		—		1,170		1,170
	$	—	$	597	$	1,170	$	1,767

- Definition

Tabular disclosure related to assets and liabilities by class, including financial instruments measured at fair value that are classified in shareholders' equity, if any, that are measured at fair value on a recurring and/or nonrecurring basis in periods after initial recognition. Disclosures include, but are not limited to: (a) the fair value measurements recorded and the reasons for the measurements and (b) the level within the fair value hierarchy in which the fair value measurements are categorized in their entirety (levels 1, 2, 3) as well as transfers between levels 1 and 2.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
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-Name Statement of Financial Accounting Standard (FAS)
-Number 157
-Paragraph 32
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 157
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Reference 7: http://www.xbrl.org/2003/role/presentationRef
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-Number 157
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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

- Definition

Tabular disclosure of the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments, assets, and liabilities. Such certain disclosures about the financial instruments, assets, and liabilities include: (1) the fair value of the required items together with their carrying amounts (as appropriate) and (2) the methodology and assumptions used in developing such estimates of fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 12
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13433-108611

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 159
-Paragraph 19
-Subparagraph a, b, c(1), d(1)
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 14
-Subparagraph a
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 15
-Subparagraph b-d
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 159
-Paragraph 18
-Subparagraph c(2), d, e, f
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 157
-Paragraph 32
-Subparagraph a, c(1), c(2), c(3), d
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 10
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Cash, Money Market Funds and Marketable Securities (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended	134 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Mar. 31, 2013	Dec. 31, 2011
Cash, Money Market Funds, and Marketable Securities
Cash and cash equivalents, Amortized Cost	$ 26,736	$ 24,523	$ 33,971	$ 26,736	$ 25,668
Cash and cash equivalents, Fair Value	26,736		33,971	26,736
Marketable securities, Amortized Cost	58,000		65,137	58,000
Unrealized Gain	28		25	28
Unrealized Loss	(13)		(11)	(13)
Marketable securities, Fair Value	58,015		65,151	58,015
Cash and marketable securities, Amortized Cost	84,736		99,108	84,736
Cash and marketable securities, Fair Value	84,751		99,122	84,751
Available-for-sale investments
Unrealized holding gains included in statements of comprehensive income	1	33	10	15
Realized gain (loss) on securities available-for-sale	0		0
Fair value of available for sale securities in unrealized loss positions	26,100		33,100	26,100
Changes in AOCI associated with the unrealized holding gain on available-for-sale investments
Balance, beginning	14	4	4
Current period changes in fair value	1	33	10	15
Balance, ending	15	$ 37	14	15
Corporate debt securities
Cash, Money Market Funds, and Marketable Securities
Marketable securities, Amortized Cost	35,934		42,503	35,934
Unrealized Gain	3		5	3
Unrealized Loss	(13)		(11)	(13)
Marketable securities, Fair Value	35,924		42,497	35,924
Commercial paper
Cash, Money Market Funds, and Marketable Securities
Marketable securities, Amortized Cost	21,716		19,725	21,716
Unrealized Gain	25		19	25
Marketable securities, Fair Value	21,741		19,744	21,741
Certificate of deposit
Cash, Money Market Funds, and Marketable Securities
Marketable securities, Amortized Cost	350		2,909	350
Unrealized Gain			1
Marketable securities, Fair Value	$ 350		$ 2,910	$ 350

Stockholders' Equity (Details) $ / shares in Units, $ in Thousands				1 Months Ended				3 Months Ended	134 Months Ended
	Jul. 26, 2012 USD ($)	Jul. 17, 2012 USD ($) $ / shares shares	Oct. 28, 2010 USD ($) $ / shares shares	Jul. 31, 2012 $ / shares shares	Mar. 31, 2012 USD ($) $ / shares shares	Oct. 31, 2010 USD ($) $ / shares shares	Mar. 31, 2010 USD ($) $ / shares shares	Mar. 31, 2012 USD ($) $ / shares	Mar. 31, 2013 USD ($) item shares	Dec. 31, 2012 shares
Stockholders' Equity
Authorized number of shares of common stock									125,000,000	125,000,000
Voting right for each share held, number \| item									1
Collaborative Agreements
Stock issued from collaboration agreement (in shares)							4,900,000
Common stock issued (in shares)					11,500,000		4,950,000
Offering price (in dollars per share) \| $ / shares					$ 5.70		$ 3.74	$ 5.70
Aggregate offering proceeds from issuance of common stock (in dollars) \| $							$ 18,500	$ 65,600
Warrants issued (in shares)							1,900,000
Number of common stock sold in a unit (in shares)							1
Number of warrants sold in a unit (in shares)							1
Portion of share purchased against a unit							0.375
Warrant term							4 years
Exercise period of warrants on or after date of issue							6 months
Exercise price of warrants (in dollars per share) \| $ / shares							4.43
Proceeds from the issuance of common stock and warrants (in dollars) \| $					$ 62,000		$ 17,100	$ 62,063	$ 193,441
Warrants outstanding									1,400,000
GSK \| SPA
Collaborative Agreements
Stock issued from collaboration agreement (in shares)		2,900,000		2,900,000
Offering price (in dollars per share) \| $ / shares		$ 6.30		$ 6.30
Total purchase price (in dollars) \| $	$ 18,600	$ 18,600
Ownership position in the company (as a percent)									19.80%
GSK \| Original Collaboration Agreement
Collaborative Agreements
Stock issued from collaboration agreement (in shares)			6,900,000			6,870,000
Offering price (in dollars per share) \| $ / shares			$ 4.56			$ 4.56
Proceeds from the issuance of common stock and warrants (in dollars) \| $			$ 31,000			$ 31,000

Stockholder's Equity (Details 3) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Stockholders' Equity
Stock-based compensation expenses	$ 1,574	$ 1,388
Stock options plans
Stockholders' Equity
Stock-based compensation expenses	1,600
Total unrecognized compensation cost related to non-vested stock options granted (in dollars)	$ 11,300
Period of recognition compensation cost	2 years 7 months 6 days
Fair value weighted-average assumptions:
Expected stock price volatility (as a percent)	82.00%	78.40%
Risk free interest rate (as a percent)	1.20%	1.10%
Expected life of options	6 years 3 months	6 years 3 months
Expected annual dividend per share (in dollars per share)	$ 0.00	$ 0.00
Number of Shares
Balance at the beginning of the period (in shares)	7,974,200
Options granted (in shares)	1,154,500
Options forfeited (in shares)	(47,600)
Balance at the end of the period (in shares)	9,081,100
Vested and unvested expected to vest at the end of the period (in shares)	8,012,500
Exercisable at the end of the period (in shares)	4,450,900
Weighted Average Exercise Price
Balance at the beginning of the period (in dollars per share)	$ 6.35
Options granted (in dollars per share)	3.53
Options forfeited (in dollars per share)	4.94
Balance at the end of the period (in dollars per share)	5.99
Vested and unvested expected to vest at the end of the period (in dollars per share)	6.10
Exercisable at the end of the period (in dollars per share)	$ 7.25
Weighted Average Remaining Contractual Life
Balance at the end of the period	7 years 6 months 4 days
Vested and unvested expected to vest at the end of the period	7 years 3 months 18 days
Exercisable at the end of the period	6 years
Aggregate Intrinsic Value
Aggregate intrinsic value of options outstanding (in dollars)	$ 207
Aggregate intrinsic value of options vested and unvested expected to vest (in dollars)	132
Aggregate intrinsic value of options exercisable (in dollars)	$ 166

Assets and Liabilities Measured at Fair Value (Details) $ in Thousands, shares in Millions	3 Months Ended		12 Months Ended	134 Months Ended
	Mar. 31, 2013 USD ($) item	Mar. 31, 2012 USD ($)	Dec. 31, 2012 USD ($) shares	Mar. 31, 2013 USD ($)	Dec. 31, 2011 USD ($)
Assets and Liabilities Measured at Fair Value
Transfer of assets from Level 1 to Level 2	$ 0			$ 0
Transfer of assets from Level 2 to Level 1	0			0
Proceeds from issuance of warrants	$ 3,300
Number of inputs used in fair value classification \| item	6
Warrants exercised (in shares) \| shares			0.5
Change in fair value of warrant liability	$ 262	$ 2,376		(1,291)
Weighted average assumptions used in the Black-Scholes valuation model for the warrants
Expected stock price volatility (as a percent)	98.80%	72.60%
Risk free interest rate (as a percent)	0.13%	0.31%
Expected life of warrants	11 months 1 day	1 year 11 months 1 day
Expected annual dividend per share (as a percent)	0.00%	0.00%
Assets:
Cash/Money market fund	$ 26,736	$ 24,523	$ 33,971	26,736	$ 25,668
Level 1
Assets:
Cash/Money market fund	26,376		33,971	26,376
Fair value of assets	26,736		33,971	26,736
Level 2
Assets:
Fair value of assets	58,015		65,151	58,015
Liabilities:
Secured debt	597		697	597
Fair value of liabilities	597		697	597
Level 2 \| Corporate debt securities
Assets:
Fair value of assets	35,924		42,497	35,924
Level 2 \| Commercial paper
Assets:
Fair value of assets	21,741		19,744	21,741
Level 2 \| Certificate of deposit
Assets:
Fair value of assets	350		2,910	350
Level 3
Liabilities:
Warrant liability	1,170		908	1,170
Fair value of liabilities	1,170		908	1,170
Total
Assets:
Cash/Money market fund	26,376		33,971	26,376
Fair value of assets	84,751		99,122	84,751
Liabilities:
Secured debt	597		697	597
Warrant liability	1,170		908	1,170
Fair value of liabilities	1,767		1,605	1,767
Total \| Corporate debt securities
Assets:
Fair value of assets	35,924		42,497	35,924
Total \| Commercial paper
Assets:
Fair value of assets	21,741		19,744	21,741
Total \| Certificate of deposit
Assets:
Fair value of assets	$ 350		$ 2,910	$ 350

Collaborative Agreements (Details) $ / shares in Units, shares in Thousands, $ in Thousands				1 Months Ended				3 Months Ended			134 Months Ended
	Jul. 26, 2012 USD ($)	Jul. 17, 2012 USD ($) item $ / shares shares	Oct. 28, 2010 USD ($) $ / shares shares	Jul. 31, 2012 USD ($) $ / shares shares	Mar. 31, 2012 USD ($) $ / shares	Oct. 31, 2010 USD ($) $ / shares shares	Mar. 31, 2010 USD ($) $ / shares shares	Mar. 31, 2013 item	Jun. 30, 2012 USD ($)	Mar. 31, 2012 USD ($) $ / shares	Mar. 31, 2013 USD ($)
Collaborative Agreements
Stock issued from collaboration agreement (in shares) \| shares							4,900
Price per share of common stock issued as part of the license and collaboration agreement (in dollars per share) \| $ / shares					$ 5.70		$ 3.74			$ 5.70
Total value of the equity investment to the company					$ 62,000		$ 17,100			$ 62,063	$ 193,441
GSK
Collaborative Agreements
Number of accounting units \| item								1
GSK \| Original Collaboration Agreement
Collaborative Agreements
Upfront payment received			$ 30,000
Potential milestone payments receivable			$ 173,500
Stock issued from collaboration agreement (in shares) \| shares			6,900			6,870
Price per share of common stock issued as part of the license and collaboration agreement (in dollars per share) \| $ / shares			$ 4.56			$ 4.56
Percentage of premium on average price per share of common stock issued as part of the license and collaboration agreement			30.00%
Period preceding the closing date of the transaction over which average price per share of the company's stock is used			60 days
Total value of the equity investment to the company			$ 31,000			$ 31,000
GSK \| Expanded Collaboration Agreement
Collaborative Agreements
Percentage of development costs funded by the entity		40.00%
Total value of the equity investment to the company				$ 18,600
Ownership position in the company (as a percent)								19.80%			19.80%
Number of exclusive licenses \| item		2
Percentage of development costs funded by the counterparty		60.00%
GSK \| SPA
Collaborative Agreements
Stock issued from collaboration agreement (in shares) \| shares		2,900		2,900
Price per share of common stock issued as part of the license and collaboration agreement (in dollars per share) \| $ / shares		$ 6.30		$ 6.30
Ownership position in the company (as a percent)								19.80%			19.80%
Total purchase price (in dollars)	$ 18,600	$ 18,600
Lock-up period for common stock issued as a part of SPA	6 months
GSK \| Clinical development objectives and the acceptance of regulatory filings milestone
Collaborative Agreements
Milestone revenue recognized									$ 3,500
GSK \| Clinical development objectives and the acceptance of regulatory filings milestone \| Original Collaboration Agreement
Collaborative Agreements
Potential milestone payments receivable			13,500						$ 3,500
GSK \| Market approvals for migalastat HCl milestone \| Original Collaboration Agreement
Collaborative Agreements
Potential milestone payments receivable			80,000
GSK \| Achievement of certain sales thresholds milestone \| Original Collaboration Agreement
Collaborative Agreements
Potential milestone payments receivable			$ 80,000
GSK \| U.S. regulatory approval milestones for migalastat HCl monotherapy and migalastat HCl-ERT co-administration
Collaborative Agreements
Percentage of development costs funded by the entity in 2012		25.00%
Percentage of development costs funded by the counterparty in 2012		75.00%
Percentage of development costs funded by the entity, thereafter		40.00%
Percentage of development costs funded by the counterparty, thereafter		60.00%
GSK \| U.S. regulatory approval milestones for migalastat HCl monotherapy and migalastat HCl-ERT co-administration \| Expanded Collaboration Agreement
Collaborative Agreements
Potential milestone payments receivable		$ 20,000
GSK \| U.S. regulatory approval milestones for migalastat HCl monotherapy and migalastat HCl-ERT co-administration \| Expanded Collaboration Agreement \| Maximum
Collaborative Agreements
Additional potential milestone payments receivable		$ 35,000
Period of additional potential milestone payments receivable		7 years

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2013	Dec. 31, 2012
Consolidated Balance Sheets
Accumulated depreciation and amortization of property and equipment (in dollars)	$ 8,872	$ 8,501
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	125,000,000	125,000,000
Common stock, shares issued	49,631,672	49,631,672
Common stock, shares outstanding	49,631,672	49,631,672

Short-Term Borrowings and Long-Term Debt	3 Months Ended
Short-Term Borrowings and Long-Term Debt	Mar. 31, 2013
Short-Term Borrowings and Long-Term Debt
Short-Term Borrowings and Long-Term Debt	Note 5. Short-Term Borrowings and Long-Term Debt In August 2011, the Company entered into a loan and security agreement (the “2011 Loan Agreement”) with Silicon Valley Bank (SVB), in order to finance certain capital expenditures anticipated to be made by the Company in connection with its move in March 2012 to new office and laboratory space in Cranbury, New Jersey. The 2011 Loan Agreement provides for up to $3 million of equipment financing through January 2014. Borrowings under the 2011 Loan Agreement are collateralized by equipment purchased with the proceeds of the loan and bear interest at a variable rate of SVB prime + 2.5%. The current SVB prime rate is 4.0%. In February 2012, the Company borrowed approximately $1.0 million from the 2011 Loan Agreement which will be repaid over the following 2.5 years. The 2011 Loan Agreement contains customary terms and conditions, including a financial covenant whereby the Company must maintain a minimum amount of liquidity measured at the end of each month where unrestricted cash, cash equivalents, and marketable securities, are greater than $20 million plus outstanding debt due to SVB. The Company has at all times been in compliance with these covenants during the term of the agreement. At March 31, 2013, the total amount due under the 2011 Loan Agreement was $0.6 million. The carrying amount of the Company’s borrowings approximates fair value at March 31, 2013.

Subsequent Events	3 Months Ended
Subsequent Events	Mar. 31, 2013
Subsequent Events
Subsequent Events	Note 8. Subsequent Events The Company evaluated events that occurred subsequent to March 31, 2013 and there were no material recognized or non-recognized subsequent events during this period.

Short-Term Borrowings and Long-Term Debt (Details) - 2011 Loan Agreement - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Feb. 29, 2012	Mar. 31, 2013
Short-Term Borrowings and Long-Term Debt
Maximum amount of loan		$ 3.0
Variable interest rate base, SVB prime rate		SVB prime
Percentage points added to the reference rate		2.50%
SVB prime rate (as a percent)		4.00%
Amount borrowed	$ 1.0
Period for repayment of debt	2 years 6 months
Financial covenant, minimum amount of unrestricted cash, cash equivalents and marketable securities plus all outstanding borrowings		$ 20.0
Amount outstanding		$ 0.6

Description of Business and Significant Accounting Policies (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands				1 Months Ended				3 Months Ended	134 Months Ended
	Jul. 26, 2012	Jul. 17, 2012	Oct. 28, 2010	Jul. 31, 2012	Mar. 31, 2012	Oct. 31, 2010	Mar. 31, 2010	Mar. 31, 2012	Mar. 31, 2013	Dec. 31, 2012
Corporate Information, Status of Operations and Management Plans
Price per share of common stock issued as part of the license and collaboration agreement (in dollars per share)					$ 5.70		$ 3.74	$ 5.70
Accumulated deficit									$ (336,347)	$ (318,889)
Common stock issued (in shares)					11,500		4,950
Warrants issued (in shares)							1,900
Proceeds from the issuance of common stock and warrants (in dollars)					$ 62,000		$ 17,100	$ 62,063	$ 193,441
Stock issued from collaboration agreement (in shares)							4,900
GSK \| Original Collaboration Agreement
Corporate Information, Status of Operations and Management Plans
Price per share of common stock issued as part of the license and collaboration agreement (in dollars per share)			$ 4.56			$ 4.56
Proceeds from the issuance of common stock and warrants (in dollars)			$ 31,000			$ 31,000
Stock issued from collaboration agreement (in shares)			6,900			6,870
GSK \| Expanded Collaboration Agreement
Corporate Information, Status of Operations and Management Plans
Percentage of development costs funded by the entity		40.00%
Percentage of development costs funded by the counterparty		60.00%
Ownership position in the company (as a percent)									19.80%
Common stock issued (in shares)				2,900
Proceeds from the issuance of common stock and warrants (in dollars)				$ 18,600
GSK \| SPA
Corporate Information, Status of Operations and Management Plans
Price per share of common stock issued as part of the license and collaboration agreement (in dollars per share)		$ 6.30		$ 6.30
Total purchase price (in dollars)	$ 18,600	$ 18,600
Ownership position in the company (as a percent)									19.80%
Stock issued from collaboration agreement (in shares)		2,900		2,900

Stockholder's Equity (Details 2) - USD ($) $ in Thousands	3 Months Ended
Stockholder's Equity (Details 2) - USD ($) $ in Thousands	Mar. 31, 2013	Mar. 31, 2012
Stock compensation expense
Total stock compensation expense	$ 1,574	$ 1,388
Research and development expense
Stock compensation expense
Total stock compensation expense	924	873
General and administrative expense
Stock compensation expense
Total stock compensation expense	$ 650	$ 515