PTC Therapeutics (PTCT) 10-K 2 Mar 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2014	Feb. 24, 2015	Jun. 30, 2014
Document and Entity Information
Entity Registrant Name	PTC THERAPEUTICS, INC.
Entity Central Index Key	1070081
Document Type	10-K
Document Period End Date	31-Dec-14
Amendment Flag	FALSE
Current Fiscal Year End Date	-19
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Public Float			$683,512,510
Entity Common Stock, Shares Outstanding		33,688,913
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$49,748,000	$15,414,000
Marketable securities	265,493,000	127,053,000
Prepaid expenses and other current assets	3,885,000	1,599,000
Receivables, net	4,445,000	958,000
Total current assets	323,571,000	145,024,000
Fixed assets, net	9,159,000	6,730,000
Deposits and other assets	489,000	149,000
Total assets	333,219,000	151,903,000
Current liabilities:
Accounts payable and accrued expenses	29,121,000	12,207,000
Current portion of long-term debt		49,000
Deferred revenue	3,354,000	878,000
Total current liabilities	32,475,000	13,134,000
Other long-term liabilities	2,277,000	2,227,000
Total liabilities	34,752,000	15,361,000
Stockholders' equity:
Common stock, $0.001 par value. Authorized 125,000,000 shares; issued and outstanding 32,898,392 shares at December 31, 2014. Authorized 125,000,000 shares; issued and outstanding 23,803,282 shares at December 31, 2013	33,000	24,000
Additional paid-in capital	721,722,000	465,246,000
Accumulated other comprehensive (loss) income	-737,000	70,000
Accumulated deficit	-422,551,000	-328,798,000
Total stockholders' equity	298,467,000	136,542,000
Total liabilities and stockholders' equity	$333,219,000	$151,903,000

Consolidated_Balance_sheets_Pa

Consolidated Balance sheets (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Consolidated Balance Sheets
Preferred stock, par value (in dollars per share)	$0.00	$0.00
Preferred stock, undesignated shares	5,000,000	5,000,000
Preferred stock, issued shares	0	0
Preferred stock, outstanding shares	0	0
Common stock, par value (in dollars per share)	$0.00	$0.00
Common stock, authorized shares	125,000,000	125,000,000
Common stock, issued shares	32,898,392	23,803,282
Common stock, outstanding shares	32,898,392	23,803,282

Consolidated_Statements_of_Ope

Consolidated Statements of Operations (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues:
Net product revenue	$717
Collaboration revenue	22,246	31,326	28,779
Grant revenue	2,282	3,370	5,167
Total revenues	25,245	34,696	33,946
Operating expenses:
Research and development	79,838	54,875	46,139
Selling, general and administrative	44,820	25,219	14,615
Total operating expenses	124,658	80,094	60,754
Loss from operations	-99,413	-45,398	-26,808
Interest income (expense), net	1,180	-6,084	-1,210
Loss on extinguishment of debt		-130
Other income (expense), net	-213	38	1,783
Loss from operations before tax benefit	-98,446	-51,574	-26,235
Net tax benefit	4,693
Net loss	-93,753	-51,574	-26,235
Deemed dividend		-18,249
Gain on exchange of convertible preferred stock in connection with recapitalization		3,391	159,954
Less beneficial conversion charge			-378
Net (loss) income attributable to common stockholders	($93,753)	($66,432)	$133,341
Net (loss) income attributable to common stockholders per share:
Basic net income (loss) per common share	($2.97)	($5.18)	$219.76
Diluted net income (loss) per common share	($2.97)	($5.18)	$42.50
Weighted-average shares outstanding:
Basic (in shares)	31,565,310	12,829,411	3,328
Diluted (in shares)	31,565,310	12,829,411	17,205

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Loss (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Consolidated statements of comprehensive loss
Net loss	($93,753)	($51,574)	($26,235)
Other comprehensive (loss) income:
Unrealized (loss) gain on marketable securities	-457	70
Foreign currency translation loss	-350
Comprehensive loss	($94,560)	($51,504)	($26,235)

Consolidated_Statements_of_Con

Consolidated Statements of Convertible Preferred Stock and Changes in Stockholders' Equity (Deficit) (USD $)	Series A-G convertible preferred stock	Series One-Three convertible preferred stock	Series Four convertible preferred stock	Series Five convertible preferred stock	Common stock	Additional paid-in capital	Accumulated other comprehensive income (loss)	Accumulated deficit	Total
Balance at Dec. 31, 2011					$133	$12,007,007		($250,611,829)	($238,604,689)
Balance, beginning of period at Dec. 31, 2011	214,379,914
Balance (in shares) at Dec. 31, 2011					132,122
Balance, beginning of period (in shares) at Dec. 31, 2011	154,728,267
Increase (decrease) in temporary equity
Issuance and exchange of series of convertible preferred stock for series of convertible preferred stock	-211,423,085	80,823,768
Issuance and exchange of series of convertible preferred stock for series of convertible preferred stock (in shares)	-149,560,902	15,038,259
Conversion of series of convertible preferred stock to common stock	-2,956,829
Conversion of series of convertible preferred stock to common stock (in shares)	-5,167,365
Increase (Decrease) in Stockholders' Equity
Issuance and exchange of series of convertible preferred stock for series of convertible preferred stock						159,954,069			159,954,069
Conversion of series of convertible preferred stock to common stock					412	2,956,417			2,956,829
Conversion of series of convertible preferred stock to common stock (in shares)					413,223
Beneficial conversion charge						377,787		-377,787
Share-based compensation expense						2,288,392			2,288,392
Net loss								-26,235,102	-26,235,000
Balance at Dec. 31, 2012					545	177,583,672		-277,224,718	-99,640,501
Balance, end of period at Dec. 31, 2012		80,823,768
Balance (in shares) at Dec. 31, 2012					545,345
Balance, end of period (in shares) at Dec. 31, 2012		15,038,259
Increase (decrease) in temporary equity
Issuance and exchange of series of convertible preferred stock for series of convertible preferred stock		-80,823,768	60,785,363	101,681,783
Issuance and exchange of series of convertible preferred stock for series of convertible preferred stock (in shares)		-15,038,259	5,374,954	8,796,002
Conversion of series of convertible preferred stock to common stock			-60,785,363	-101,681,783
Conversion of series of convertible preferred stock to common stock (in shares)			-5,374,954	-8,796,002
Increase (Decrease) in Stockholders' Equity
Reverse stock split					-540,819
Issuance and exchange of series of convertible preferred stock for series of convertible preferred stock						-14,857,927			-14,857,927
Issuance of common stock from IPO and exercise of over allotment exercise, net of offering costs					9,628	131,640,060			131,649,688
Issuance of common stock from IPO and exercise of over allotment exercise, net of offering costs (in shares)					9,627,800
Conversion of series of convertible preferred stock to common stock					14,171	162,452,975			162,467,146
Conversion of series of convertible preferred stock to common stock (in shares)					14,170,956
Share-based compensation expense						8,427,188			8,427,188
Net loss								-51,573,575	-51,574,000
Comprehensive income (loss)							70,393		70,000
Balance at Dec. 31, 2013					24,344	465,245,968	70,393	-328,798,293	136,542,000
Balance (in shares) at Dec. 31, 2013					23,803,282
Increase (Decrease) in Stockholders' Equity
Exercise of stock options					109	1,195,286			1,195,395
Exercise of stock options (in shares)					108,645
Vesting of restricted stocks					373	-373
Vesting of restricted stock (in shares)					373,200
Issuance of common stock from IPO and exercise of over allotment exercise, net of offering costs					8,072	235,971,025			235,979,097
Issuance of common stock from IPO and exercise of over allotment exercise, net of offering costs (in shares)					8,613,265
Share-based compensation expense						19,309,652			19,309,652
Net loss								-93,753,493	-93,753,000
Comprehensive income (loss)							-807,058		-807,058
Balance at Dec. 31, 2014					$32,898	$721,721,558	($736,665)	($422,551,786)	$298,467,000
Balance (in shares) at Dec. 31, 2014					32,898,392

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities
Net loss	($93,753)	($51,574)	($26,235)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	2,235	2,396	2,704
Change in valuation of warrant liability	130	-38	-1,783
Non-cash interest expense		6,049	226
Loss on extinguishment of debt		130
Share-based compensation expense	19,310	8,427	2,289
Amortization of premiums on investments	1,607
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	-2,286	-760	2,452
Receivables, net	-3,487	56	230
Deposits and other assets	-340	48	84
Accounts payable and accrued expenses	16,914	5,183	-6,026
Other long-term liabilities	-80	-285	103
Deferred revenue	2,476	-16,554	-21,972
Net cash used in operating activities	-57,274	-46,922	-47,928
Cash flows from investing activities
Purchases of fixed assets	-4,664	-846	-189
Purchases of marketable securities	-247,804	-156,045
Sale & redemption of marketable securities	107,300	29,062
Net cash used in investing activities	-145,168	-127,829	-189
Cash flows from financing activities
Payments on long-term debt	-49	-4,996	-6,944
Net proceeds from sale of Series One preferred stock			29,355
Net proceeds from sale of Series Four convertible preferred stock		60,785
Net proceeds from public offerings	235,979	131,650
Proceeds from exercise of options	1,196
Net cash provided by financing activities	237,126	187,439	22,411
Effect of exchange rate changes on cash	-350
Net increase (decrease) in cash and cash equivalents	34,334	12,688	-25,706
Cash and cash equivalents, beginning of period	15,414	2,726	28,432
Cash and cash equivalents, end of period	49,748	15,414	2,726
Supplemental disclosure of cash information
Cash paid for interest	1	367	1,212
Cash paid for income taxes		2	2
Supplemental disclosures of non-cash information related to investing and financing activities
Change in unrealized gain (loss) on marketable securities	-457	70
Change in carry value of preferred securities resulting from recapitalization		$3,391	$159,954

The_Company

The Company	12 Months Ended
	Dec. 31, 2014
The Company
The Company	1. The Company
	PTC Therapeutics, Inc. (the Company or PTC) was incorporated as a Delaware corporation on March 31, 1998. PTC is a global biopharmaceutical company focused on the discovery, development and commercialization of orally administered, small molecule therapeutics targeting an area of RNA biology referred to as post-transcriptional control. The letters "PTC" in the corporate name are an acronym for post-transcriptional control processes, which are the regulatory events that occur in cells during and after a messenger RNA is copied from DNA through the transcription process. The Company has discovered all of its compounds currently under development using its proprietary technologies. The Company plans to continue to develop these compounds both on its own and through selective collaboration arrangements with leading pharmaceutical and biotechnology companies. The Company believes that systematically targeting post-transcriptional control processes represents an unexploited approach to drug discovery and development. The Company's internally discovered pipeline addresses multiple therapeutic areas, including rare disorders, oncology and infectious diseases
	The Company's lead product, Translarna™ (ataluren) received marketing authorization from the European Commission, or EC, in August 2014 for the treatment of nonsense mutation Duchenne muscular dystrophy, or nmDMD, in ambulatory patients age 5 years and over in the 31 member states of the European Economic Area, or EEA. nmDMD is a rare, life threatening disorder. This marketing authorization is subject to annual review and renewal by the European Medicines Agency, or EMA following its reassessment of the risk-benefit balance of the authorization and is further conditioned on the Company's ability to complete its global, confirmatory Phase 3 clinical trial in nmDMD, which it refers to as ACT DMD, and submit the final report, including additional efficacy and safety data from the trial, during 2015. See "Business—Regulation in the European Union" and "Risk Factors—Risks Related to Regulatory Approval of our Product Candidates" for further detail regarding the EMA's approval process, including a description of the risk-benefit balance.
	The Company launched Translarna on a commercial basis in Germany in December 2014 and expects to expand its launch activities across the EEA throughout 2015 and future years, subject to successful completion of pricing and reimbursement negotiations. Concurrently, the Company has been pursuing reimbursed early access programs in selected countries where those mechanisms exist, both within Europe and in those countries outside of Europe that will reference the marketing authorization described above.
	The Company has not generated significant product revenue to date and is subject to a number of risks similar to those of other early stage companies, including dependence on key individuals, the difficulties inherent in the development of commercially usable products, the potential need to obtain additional capital necessary to fund the development of its products, and competition from other companies. As of December 31, 2014, the Company had an accumulated deficit of approximately $422.6 million. The Company has financed its operations to date primarily through public offerings of common stock in February 2014 and October 2014, its initial public offering of common stock in June 2013 (see Note 7 below), private placements of its convertible preferred stock, collaborations, bank debt, convertible debt financings, grant funding and clinical trial support from governmental and philanthropic organizations and patient advocacy groups in the disease area addressed by the Company's product candidates.

Summary_of_significant_account

Summary of significant accounting policies	12 Months Ended
	Dec. 31, 2014
Summary of significant accounting policies
Summary of significant accounting policies
	2. Summary of significant accounting policies
	Basis of presentation
	The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) and include all adjustments necessary for the fair presentation of the Company's financial position for the periods presented.
	Use of estimates
	The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
	Consolidation
	The consolidated financial statements include the accounts of PTC Therapeutics, Inc. and our wholly owned subsidiaries. All inter-company accounts, transactions, and profits have been eliminated in consolidation.
	Segment and geographic information
	Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating and reporting segment.
	Cash equivalents
	The Company considers all highly liquid investments with a maturity of 90 days or less at the time of purchase to be cash equivalents. Cash equivalents are carried at cost which approximates fair value due to their short-term nature.
	Marketable securities
	The Company considers securities with original maturities of greater than 90 days to be available for sale securities. Securities under this classification are recorded at fair value and unrealized gains and losses within accumulated other comprehensive income. The estimated fair value of the available for sale securities is determined based on quoted market prices or rates for similar instruments. In addition, the cost of debt securities in this category is adjusted for amortization of premium and accretion of discount to maturity. The Company evaluates securities with unrealized losses to determine whether such losses, if any, are other than temporary.
	Fixed assets
	Fixed assets are stated at cost. Depreciation is computed starting when the asset is placed into service on a straight-line basis over the estimated useful life of the related asset as follows:
	Leasehold improvements		Lesser of useful life or lease term
	Computer equipment and software		3 years
	Furniture, fixtures, and lab equipment		3 to 7 years
	Concentration of credit risk
	The Company's financial instruments that are exposed to credit risks consist primarily of cash and cash equivalents, available-for-sale marketable securities and accounts receivable. The Company maintains its cash and cash equivalents in bank accounts, which, at times, exceed federally insured limits. The Company has not experienced any credit losses in these accounts and does not believe it is exposed to any significant credit risk on these funds. The Company's investment policy includes guidelines on the quality of the financial institutions and financial instruments the Company is allowed to invest in, which the Company believes minimizes the exposure to concentration of credit risk.
	The Company is subject to credit risk from its accounts receivable related to its product sales revenue of Translarna. The payment terms are predetermined and the Company evaluates the creditworthiness of each customer or distributor on a regular basis. The Company periodically assesses the financial strength of the holders of its accounts receivable to establish allowances for anticipated losses, if necessary. The Company reserves all uninsured amounts billed directly to a patient until the time of cash receipt as collectability is not reasonably assured at the time the product is received. To date, the Company has not incurred any credit losses.
	Inventories and cost of product revenue
	On August 4, 2014, the Company was notified that the European Commission, or EC, granted conditional marketing authorization for Translarna for the treatment of Duchenne muscular dystrophy caused by nonsense mutations, or nmDMD, in ambulatory patients aged five years and older. The conditional marketing authorization allows the Company to market Translarna in the European Economic Area, or EEA, which is comprised of the 28 member states of the European Union plus Norway, Iceland and Liechtenstein. The conditional marketing authorization is subject to an annual review by the European Medicines Agency, or EMA, and the Company will seek to renew the approval on an annual basis until the Company's obligations have been fulfilled and the approval is converted from a conditional approval into a full approval. The launch in these countries is on a country by country basis. The Company does do not have sufficient history or experience from which to accurately forecast product sales or demand generation. As such, the Company has not capitalized inventory and will not capitalize inventory until full approval has been obtained or until the Company can reasonably predict future product sales. The costs incurred related to the manufacturing of Translarna have been recorded as research and development expense in the statements of operations. The Company's cost of product sales includes royalties and other miscellaneous selling costs, which were not material for the year ended 2014 and therefore included as a component of research and development costs in the current year presentation. The time period over which this inventory is consumed will depend on a number of factors, including the amount of future Translarna sales, and the ability to utilize inventory prior to its expiration date.
	Deferred rent
	The Company has an operating lease for office space. Rent expense is recorded on a straight-line basis over the initial lease term. The difference between the actual cash paid and the straight-line rent expense is recorded as deferred rent. Leasehold improvements made related to this lease, subsequent to its inception, are amortized over the remaining lease term.
	Accumulated other comprehensive income (loss)
	Accumulated other comprehensive income (loss) consists of unrealized gains or losses on marketable securities and foreign currency translation adjustments.
	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.
	Net Product Sales
	PTC's net product sales have consisted solely of sales of Translarna for the treatment of DMD caused by nonsense mutations. The Company applies the revenue recognition guidance in accordance with Financial Accounting Standards Board ("FASB") Accounting Standards Codification ("ASC") Subtopic 605-15, Revenue Recognition—Products. The Company recognizes revenue from product sales when there is persuasive evidence that an arrangement exists, title to product and associated risk of loss has passed to the customer, the price is fixed or determinable, collectability is reasonably assured and the Company has no further performance obligations.
	The Company has recorded revenue on sales where Translarna is available on a reimbursed early access program and typically paid for by a government authority or institution. The Company generally recognizes revenue for these named patient or cohort early access programs on a cash basis if all other revenue recognition criteria have been met. Once the Company has established a pattern of collectability, revenue will be recorded upon shipment assuming all other revenue recognition criteria are met.
	The Company records revenue net of estimated discounts and rebates. Allowances are recorded as a reduction of revenue at the time revenues from product sales are recognized. Allowances for government rebates and discounts are established at the time of delivery. These allowances are adjusted to reflect known changes in factors and may impact such allowances in the quarter those changes are known.
	Collaboration and Grant Revenue
	The terms of these agreements typically include payments to the Company of one or more of the following: nonrefundable, upfront license fees; milestone payments; research funding and royalties on future product sales. In addition, the Company generates service revenue through agreements that generally provide for fees for research and development services and may include additional payments upon achievement of specified events.
	The Company evaluates all contingent consideration earned, such as a milestone payment, using the criteria as provided by the Financial Accounting Standards Board (FASB), guidance on the milestone method of revenue recognition. At the inception of a collaboration arrangement, the Company evaluates if milestone payments are substantive. The criteria requires that (1) the Company determines if the milestone is commensurate with either its performance to achieve the milestone or the enhancement of value resulting from our activities to achieve the milestone; (2) the milestone be related to past performance; and (3) 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. The Company recognizes royalties as earned in accordance with the terms of various research and collaboration agreements. If not substantive, the contingent consideration is allocated to the existing units of accounting based on relative selling price and recognized following the same basis previously established for the associated unit of accounting.
	The Company recognizes revenue for reimbursements of research and development costs under collaboration agreements as the services are performed. The Company records these reimbursements as revenue and not as a reduction of research and development expenses as the Company has the risks and rewards as the principal in the research and development activities.
	Research and development costs
	Research and development expenses include the clinical development costs associated with the Company's product development programs and research and development costs associated with the Company's discovery programs. These expenses include internal research and development costs and the costs of research and development conducted on behalf of the Company by third parties, including sponsored university-based research agreements and clinical study vendors. All research and development costs are expensed as incurred. Costs incurred in obtaining technology licenses are charged immediately to research and development expense if the technology licensed has not reached technological feasibility and has no alternative future uses.
	Nonrefundable advance payments made for goods and services that will be used in future research and development activities are deferred if the contracted party has not yet performed the related activities. The amount deferred is then recognized as expense when the research and development activities are performed. The deferred research and development advance payments were $0.9 million as of December 31, 2014 and not significant as of December 31, 2013.
	Fair value of financial instruments
	The Company follows the fair value measurement rules, which provides guidance on the use of fair value in accounting and disclosure for assets and liabilities when such accounting and disclosure is called for by other accounting literature. These rules establish a fair value hierarchy for inputs to be used to measure fair value of financial assets and liabilities. This hierarchy prioritizes the inputs to valuation techniques used to measure fair value into three levels: Level 1 (highest priority), Level 2, and Level 3 (lowest priority).
	•	Level 1—Unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the balance sheet date.
	•	Level 2—Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. Level 2 inputs include quoted prices for similar assets and liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability (i.e., interest rates, yield curves, etc.), and inputs that are derived principally from or corroborated by observable market data by correlation or other means (market corroborated inputs).
	•	Level 3—Inputs are unobservable and reflect the Company's assumptions as to what market participants would use in pricing the asset or liability. The Company develops these inputs based on the best information available.
	Cash equivalents and investments are reflected in the accompanying financial statements at fair value. The carrying amount of receivables and accounts payable and accrued expenses approximates fair value due to the short-term nature of those instruments.
	Beneficial conversion
	When the Company issues a debt or an equity security that is convertible into common stock at a discount from the fair value of the common stock at the date the debt or equity security counterparty is legally committed to purchase such a security (Commitment Date), a beneficial conversion charge is measured and recorded on the Commitment Date for the difference between the fair value of the Company's common stock and the effective conversion price of the convertible debt or equity security. If the intrinsic value of the beneficial conversion feature is greater than the proceeds allocated to the convertible debt or equity security, the amount of the discount assigned to the beneficial conversion feature is limited to the amount of the proceeds allocated to the convertible debt or equity security.
	The amount allocated to the beneficial conversion feature is presented as a discount or reduction to the related debt security or as an immediate charge to earnings available to common shareholders for convertible preferred stock instruments that are convertible by the shareholders at any time. In connection with the Company's recapitalization of its outstanding convertible preferred stock in 2012, the Company recorded a beneficial conversion charge representing the difference between the effective conversion price and the fair value of the Company's common stock as of the Commitment Date. Because the intrinsic value was in excess of the proceeds allocated to the Company's new Series Three convertible preferred stock; the beneficial conversion charge was limited to the allocated proceeds of approximately $0.4 million.
	Warrant liability
	Warrants to purchase the Company's common stock with nonstandard antidilution provisions, regardless of the probability or likelihood that may conditionally obligate the issuer to ultimately transfer assets, are classified as liabilities and are recorded at their estimated fair value at each reporting period. Any change in fair value of these warrants is recorded as gain/(loss) on warrant valuation each reporting period in Other income/(expense) on the Company's statement of operations.
	Impairment of long-lived assets
	The Company monitors its long-lived assets for indicators of impairment. If such indicators are present, the Company assesses the recoverability of affected assets by determining whether the carrying value of such assets is less than the sum of the undiscounted future cash flows of the assets. If such assets are found not to be recoverable, the Company measures the amount of such impairment by comparing the carrying value of the assets to the fair value of the assets, with the fair value generally determined based on the present value of the expected future cash flows associated with the assets. Although current and historical negative cash flows are indicators of impairment, management believes the future cash flows to be received from the long-lived assets and the potential success of the Company's research programs will exceed the assets' carrying value, and accordingly, the Company believes that no impairment of long-lived assets exists as of December 31, 2014.
	Share-based compensation
	The Company measures the cost of employee services received in exchange for an award of equity instruments based on the grant date fair value of the award. Restricted stock awards are measured based on the fair market values of the underlying stock on the dates of grant. For service type awards, share-based compensation expense is recognized on a straight-line basis over the period during which the employee is required to provide service in exchange for the entire award. For awards that vest or begin vesting upon achievement of a performance condition, the Company estimates the likelihood of satisfaction of the performance condition and recognizes compensation expense when achievement of the performance condition is deemed probable using an accelerated attribution model.
	The fair value of options is calculated using the Black-Scholes option pricing model to determine the fair value of stock options on the date of grant based on key assumptions such as expected volatility and expected term. As a new public company, the Company does not have sufficient history to estimate the volatility of its common stock price or the expected life of the options. The Company calculates expected volatility based on reported data for similar publicly traded companies for which historical information is available and will continue to do so until the historical volatility of its common stock is sufficient to measure expected volatility for future option grants.
	Income taxes
	Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and net operating loss and credit carryforwards. Deferred tax assets and liabilities are measured at rates expected to apply to taxable income in the years in which those temporary differences and carryforwards are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in the statement of operations in the period that includes the enactment date. A valuation allowance is recorded when it is not more likely than not that all or a portion of the net deferred tax assets will be realized.
	Net tax benefit
	The Company recognized a tax benefit of $4.9 million related to the sale of net operating losses in the New Jersey Technology Business Tax Certificate Transfer Program for the year ended December 31, 2014. We did not participate in this program during the year ended December 31, 2013.
	Net (loss) income per share
	Basic net income per share is calculated by dividing the net income attributable to common stockholders by the weighted average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net income per share is calculated by dividing the net income attributable to common stockholders by the weighted-average number of common share equivalents outstanding for the period determined using the treasury-stock method and the if-converted method. During periods in which the Company incurs net losses, both basic and diluted loss per share is calculated by dividing the net loss by the weighted average shares outstanding—potentially dilutive securities are excluded from the calculation because their effect would be anti-dilutive. Dilutive common stock equivalents are comprised of convertible preferred stock and options outstanding under the Company's stock option plans.
	In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers. ASU 2014-09 will eliminate transaction- and industry-specific revenue recognition guidance under current GAAP and replace it with a principle-based approach for determining revenue recognition. ASU 2014-09 will require that companies recognize revenue based on the value of transferred goods or services as they occur in the contract. The ASU also will require additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. ASU 2014-09 is effective for annual reporting periods beginning after December 15, 2016. Early application is not permitted. Entities can transition to the standard either retrospectively or as a cumulative-effect adjustment as of the date of adoption. Presently, the Company is assessing what effect the adoption of ASU 2014-09 will have on its financial statements and accompanying notes.

Fair_value_of_financial_instru

Fair value of financial instruments and investments	12 Months Ended
	Dec. 31, 2014
Fair value of financial instruments and investments
Fair value of financial instruments and investments	3. Fair value of financial instruments and investments
	Fair value of certain investments is based upon market prices using quoted prices in active markets for identical assets quoted on the last day of the year. In establishing the estimated fair value of the remaining investments, the Company used the fair value as determined by its investment advisors using observable inputs other than quoted prices.
	The Company reviews its investments on a periodic basis for other-than-temporary impairments. This review is subjective, as it requires management to evaluate whether an event or change in circumstances has occurred in that period that may have a significant adverse effect on the fair value of the investment.
	The following represents the fair value using the hierarchy described in Note 2 for the Company's financial assets and liabilities that are required to be measured at fair value on a recurring basis as of December 31, 2014 and 2013:
		December 31, 2014
		Total			Quoted prices		Significant			Significant
					in active		other			unobservable
					markets for		observable			inputs
					identical assets		inputs			(level 3)
					(level 1)		(level 2)
	Marketable securities	$	265,493		$	—	$	265,493		$	—
	Warrant liability	$	188		$	—	$	—		$	188
		December 31, 2013
		Total			Quoted prices		Significant			Significant
					in active		other			unobservable
					markets for		observable			inputs
					identical assets		inputs			(level 3)
					(level 1)		(level 2)
	Marketable securities	$	127,053		$	—	$	127,053		$	—
	Warrant liability	$	58		$	—	$	—		$	58
	The Company uses the market approach to measure fair value for its financial assets. The market approach uses prices and other relevant information generated by market transactions involving identical or comparable assets. The Company's marketable securities investments classified as Level 2 primarily utilize broker to value these securities. No transfers of assets between Level 1 and Level 2 of the fair value measurement hierarchy occurred during the year ended December 31, 2014.
	The following is a summary of marketable securities accounted for as available-for-sale securities at December 31, 2014:
		December 31, 2014
					Gross Unrealized
		Amortized								Fair
		Cost			Gains		Losses			Value
	Corporate debt securities	$	230,379		$	80	$	(428	)	$	230,031
	Government obligations		35,501			7		(46	)		35,462
		$	265,880		$	87	$	(474	)	$	265,493
		December 31, 2013
					Gross Unrealized
		Amortized								Fair
		Cost			Gains		Losses			Value
	Commercial paper	$	14,994		$	4	$	—		$	14,998
	Corporate debt securities		111,989			97		(31	)		112,055
		$	126,983		$	101	$	(31	)	$	127,053
	Unrealized gains and losses are reported as a component of accumulated other comprehensive (loss) income in stockholders' equity. During the year ended December 31, 2014, the Company did not have any realized gains/losses from the sale of marketable securities. The cost of securities sold is based on the specific identification method. The Company evaluates investments with unrealized losses to determine if the losses are other than temporary. At December 31, 2014, the Company held securities with an unrealized loss position that were not considered to be other-than-temporarily impaired as the Company has the ability to hold such investments until recovery of their fair value. In addition, the Company considered the financial condition, credit ratings and near-term prospects of the issuers, and the magnitude of the losses as compared to the cost and the length of time the investments have been in an unrealized loss position when determining if the losses are other than temporary.
	Marketable securities on the balance sheet at December 31, 2014 mature as follows:
		December 31, 2014
		Less Than			More Than
		12 Months			12 Months
	U.S. corporate debt securities	$	157,758		$	72,273
	Government Obligations		6,003			29,459
	Total Marketable securities	$	163,761		$	101,732
	Marketable securities on the balance sheet at December 31, 2013 matured as follows:
		December 31, 2013
		Less Than			More Than
		12 Months			12 Months
	Commercial paper	$	14,998		$	—
	U.S. corporate debt securities		54,159			57,896
	Total Marketable securities	$	69,157		$	57,896
	Level 3 valuation
	The warrant liability is classified in Other long-term liabilities on the Company's balance sheet. The warrant liability is marked-to-market each reporting period with the change in fair value recorded as a gain or loss within Other income/(expense) on the Company's statement of operations until the warrants are exercised, expire or other facts and circumstances lead the warrant liability to be reclassified as an equity instrument. The fair value of the warrant liability is determined at each reporting period by utilizing the Black-Scholes option pricing model.
	The table presented below is a summary of changes in the fair value of the Company's Level 3 valuation for warrant liability for the years ended December 31, 2014 and 2013:
		Level 3 assets
	Beginning balance January 1, 2013	$	96
	Change in fair value of warrant liability		(38	)
	Ending balance as of December 31, 2013	$	58
	Change in fair value of warrant liability		130
	Ending balance as of December 31, 2014	$	188
	Fair value of the warrant liability is estimated using an option-pricing model, which includes variables such as the expected volatility based on guideline public companies, the preferred stock value, and the estimated time to a liquidity event. The significant assumptions used in preparing the option pricing model for valuing the Company's warrants as of December 31, 2014 include (i) volatility (68-70%), (ii) risk free interest rate (0.89%-1.65%), (iii) strike price ($128.00-$2,520.00), (iv) fair value of common stock ($51.77) and (v) expected life (2.5-4.7 years).The significant assumptions used in preparing the option pricing model for valuing the Company's warrants as of December 31, 2013 include (i) volatility (61-89%), (ii) risk free interest rate (0.07%-2.1%), (iii) strike price ($128.00-$2,520.00), (iv) fair value of common stock($16.97) and (v) expected life (0.3-5.7 years).

Fixed_assets

Fixed assets	12 Months Ended
	Dec. 31, 2014
Fixed assets
Fixed assets
	4. Fixed assets
	Fixed assets, net were as follows at December 31, 2014 and 2013:
		December 31,
		2014			2013
	Leasehold improvements	$	13,051		$	12,474
	Computer equipment and software		2,472			2,285
	Furniture, fixtures, and lab equipment		15,070			14,284
	Assets in process		3,483			369
			34,076			29,412
	Less accumulated depreciation and amortization		(24,917	)		(22,682	)
		$	9,159		$	6,730
	Depreciation expense was approximately $2.2 million, $2.4 million, and $2.7 million for the years ended December 31, 2014, 2013 and 2012, respectively.

Accounts_payable_and_accrued_e

Accounts payable and accrued expenses	12 Months Ended
	Dec. 31, 2014
Accounts payable and accrued expenses
Accounts payable and accrued expenses
	5. Accounts payable and accrued expenses
	Accounts payable and accrued expenses at December 31, 2014 and 2013 consist of the following:
		December 31,
		2014		2013
	Employee compensation, benefits, and related accruals	$	9,312	$	5,103
	Consulting and contracted research		9,349		4,006
	Professional fees		3,334		1,294
	Accounts payable		4,128		1,124
	Other		2,998		680
		$	29,121	$	12,207

Longterm_debt

Long-term debt	12 Months Ended
	Dec. 31, 2014
Long-term debt.
Long-term debt
	6. Long-term debt
	In September 2009, the Company entered into a $25.0 million secured debt facility with a syndicate of two lenders. The Company borrowed $12.5 million under the facility in September 2009 and an additional $10.0 million under the facility in December 2010 and issued the lenders promissory notes. The notes were secured by substantially all of the Company's assets except for intellectual property. In July 2013, the Company paid in full the outstanding principal and interest of $2.6 million due under the promissory notes issued in connection with the secured debt facility. As a result of this transaction, the Company recorded a loss on extinguishment of debt of $0.1 million on the Company's statement of operations for the year ended December 31, 2013. The loss on extinguishment of debt primarily represented the write off of related deferred financing costs, the acceleration of recognition of debt extinguishment fees and the prepayment premium payable.

Capital_structure

Capital structure	12 Months Ended
	Dec. 31, 2014
Capital structure
Capital structure
	7. Capital structure
	Convertible preferred stock prior to 2012 recapitalization
	As of December 31, 2011, the Company had authorized for issuance up to 156,995,095 shares of preferred stock, $0.001 par value. The authorized shares as of December 31, 2011 were designated as follows: 750,000 shares of Series A convertible preferred stock (Series A), 187,500 shares of Series B convertible preferred stock (Series B), 6,295,000 shares of Series C convertible preferred stock (Series C), 13,769,935 shares of Series D convertible preferred stock (Series D), 126,735,022 shares of Series E convertible preferred stock (Series E), 3,670,138 shares of Series E-2 convertible preferred stock (Series E-2), 675,000 shares of Series F convertible preferred stock (Series F), 1,612,500 shares of Series F-2 convertible preferred stock (Series F-2) and 3,300,000 shares of Series G convertible preferred stock (Series G).
	The rights and preferences of the shares of Series A, Series B, Series C, Series D, Series E, Series E-2, Series F, Series F-2 and Series G were as follows:
	Conversion—Each share of Series A, Series B, Series C, Series D, Series E, Series E-2, Series F, Series F-2 and Series G was convertible at any time at the option of the holder into such number of shares of common stock as determined by applying a conversion factor to the outstanding shares of approximately 0.0833, 0.1333, 0.1389, 0.1548, 0.0548, 1.0000, 1.0000, 1.0000 and 1.0000 for the Series A, Series B, Series C, Series D, Series E, Series E-2, Series F, Series F-2, and Series G respectively. These conversion factors were calculated based on the then-applicable conversion price with respect to each respective series of preferred stock. These conversion factors were subject to adjustment in the event the Company issued additional equity securities at prices below the then-applicable conversion price, or if the Company engaged in specified changes to its capitalization, such as stock splits or stock dividends. The conversion of each series of preferred stock would have been automatic upon the closing of a qualified initial public offering or any other public offering upon the written election of the Company and holders of both (1) at least two thirds of the outstanding preferred shares on an as-converted to common stock basis and (2) at least two thirds of the Series F, F-2 and G shares voting together as a single class on an as-converted to common stock basis.
	Voting—Each preferred shareholder was entitled to the number of votes per share as if the preferred shares were converted to common stock. Additionally, the holders of the preferred stock, voting as a single class, were entitled to elect six members of the Board of Directors.
	Liquidation—Upon the liquidation, dissolution, reorganization or winding-up of the Company, holders of preferred stock were entitled to receive, before any distribution or payment on the common stock, an amount equal to $1.00 per share for Series A, $2.00 per share for Series B, $2.50 per share for Series C, $3.25 per share for Series D, $0.397644 per share for Series E, $7.26 per share for Series E-2, $16.00 per share for Series F, $16.00 per share for Series F-2, and $16.00 per share for Series G, plus all declared, but unpaid, dividends. As of December 31, 2011, the aggregate liquidation preference was $750,000, $375,000, $15,000,000, $42,561,249, $49,999,998, $26,645,187, $10,000,000, $24,248,048, and $50,300,000 for the Series A, Series B, Series C, Series D, Series E, Series E-2, Series F, Series F-2, and Series G, respectively. In cases where the liquidation preference applied, if there were insufficient funds to pay the full preference value to all holders, then, as a group, the holders of the Series E, Series E-2, Series F, Series F-2, and Series G would have been paid together first, ratably, in proportion to their respective liquidation preferences. To the extent there were excess assets to distribute, the holders of the Series D would have been paid second. Finally, as a group, the holders of the Series A, Series B, and Series C would have been paid last, ratably, in proportion to their respective liquidation preferences. Dividends were payable only if and when declared. The Company did not declare any dividends through December 31, 2012.
	2012 Recapitalization
	In July 2012, the Company completed a recapitalization pursuant to which all outstanding shares of Series A, B, C, D, E, E-2, F, F-2, and G convertible preferred stock (Prior Series Preferred) were exchanged into Series Three convertible preferred stock (Series Three). Warrants to acquire Prior Series Preferred became warrants to acquire Series Two convertible preferred stock (Series Two). In addition, those investors that elected to participate in the sale of Series One convertible preferred stock (Series One) were entitled to exchange their Series Three shares for Series Two shares.
	In connection with the recapitalization, the Company sold 1,483,337 shares of Series One for aggregate gross proceeds of approximately $29.7 million.
	The Company accounted for the recapitalization as an extinguishment of its Prior Series Preferred and recorded the Series One, Series Two and Series Three shares at their fair value as of the recapitalization date. In accordance with authoritative accounting guidance, the Company recorded a gain attributable to the common stockholders on the extinguishment of the Prior Series Preferred. The gain of approximately $160.0 million represented the excess of the carrying amount of Prior Series Preferred stock immediately prior to the recapitalization over the fair value of the Series One, Two and Three stock issued in connection with the recapitalization.
	Valuation—The value of the Company was estimated using the probability weighted expected return method (PWERM). The PWERM considered the most significant near-term driver of value for the Company as the ability to file a marketing authorization application (MAA) with The European Medicines Agency (EMA) for conditional approval of ataluren. The Company has initiated a confirmatory Phase 3 clinical trial of ataluren for the treatment of nmDMD. If favorable, the results of the confirmatory Phase 3 clinical trial could serve as the basis for full approval by the EMA and the FDA of ataluren for the treatment of nmDMD in the European Union and the United States. The remaining scenarios in the PWERM related to funding the completion of the confirmatory Phase 3 clinical trial of ataluren for the treatment of nmDMD.
	After identifying the various potential liquidity scenarios and their likely timing, a pre-money enterprise value was assigned to each scenario based on a combination of management's guidance and recent trends in the capital markets. The resulting enterprise value for each liquidity event was divided by the total shares that would be outstanding under each scenario to arrive at a price per share for the common and preferred classes of stock. Each scenario was then assigned an outcome probability based on management's estimates. The resulting probability weighted share values were then discounted to present value at a rate that reflects general industry risks (but not Company specific risks).
	The rights and preferences of the shares of Series One, Two and Three were as follows:
	Dividends—The holders of Series One and Series Two, in preference to the holders of common stock, were entitled to noncumulative dividends when and if declared by the Board of Directors. The holders of Series Three were not entitled to dividends. The Company did not declare any dividends through December 31, 2012.
	Liquidation—Upon the liquidation, dissolution, reorganization or winding-up of the Company, the holders of Series One would have been entitled to receive, before any distribution or payment was made to any other class of security, an amount equal to two times the original issuance price, plus all declared, but unpaid, dividends. To the extent there had been excess assets to distribute, the holders of Series Two would have been be entitled to receive 76.47% of such excess assets, and the holders of Series One would have been entitled to receive 23.53% of such excess assets, until the holders of Series Two received an amount equal to one times the stated liquidation preference amount for the Series Two, plus all declared, but unpaid, dividends. In the event there had been remaining assets after Series Two distributions, the holders of Series Three would have been entitled to receive 8.82% of such remaining assets, and the holders of Series One and Series Two would have been entitled to receive 23.53% and 67.65%, respectively, of such remaining assets, until the holders of Series Three received an amount equal to one times the stated liquidation preference amount for the Series Three, plus all declared, but unpaid, dividends. To the extent there had been remaining assets to distribute, the holders of Series One, Series Two, and Series Three would have been entitled to receive 20%, 55%, and 25% of such remaining assets, respectively.
	Voting—Each holder of Series One was entitled to cast the number of votes equal to five times the number of common shares into which such holder's shares of Series One would have converted. Except as required by law, holders of Series Two and Series Three had limited voting rights. Additionally, the holders of Series One, voting as a single class, were entitled to elect twelve members of the Board of Directors.
	Conversion—Each share of Series One was convertible at any time at the option of the holder into two shares of common stock. Each share of Series Two and Series Three was convertible at any time at the option of the holder into one share of common stock. These conversion ratios were subject to adjustment for certain dilutive events, including certain types of stock splits or stock dividends or future recapitalizations.
	2013 Recapitalization
	During January and February of 2013, the Company entered into a "bridge" financing arrangement with certain existing investors providing for the issuance by the Company of an aggregate of $6 million of convertible promissory notes and warrants to purchase 2,527,675 shares of Series One and Series Two convertible preferred stock. The warrants have a per share exercise price of $0.01, and as such, they are referred to as "penny warrants". This bridge financing was closed in anticipation of the March 2013 Series Four financing event, which the Company refers to as the "2013 recapitalization".
	The Company allocated the proceeds of the convertible promissory notes between debt and warrant liability. Since the value of the warrants exceeded the proceeds from the convertible notes issued to existing investors, the value of the warrant in excess of the proceeds is considered a deemed dividend and reflected as an equity transaction in the financial statements. The Company recorded $6.0 million to interest expense related to the debt discount associated with the convertible debt during the quarter ended March 31, 2013.
	On March 7, 2013, the Company closed a private placement of a new series of convertible preferred stock that resulted in another recapitalization event (the 2013 recapitalization). In this private placement, the Company issued and sold an aggregate of 4,497,035 shares of its Series Four senior preferred stock (Series Four) for an aggregate purchase price of approximately $54 million. Including the $6.0 million raised with the bridge financing, total gross proceeds raised during the quarter ended March 31, 2013 was approximately $60.0 million. In addition, the Company issued an aggregate of 502,919 shares of Series Four upon the share settlement of the convertible promissory notes described above that were issued in January and February 2013.
	In connection with this private placement, the Company effected a one-for-120 reverse stock split of its common stock and an exchange of outstanding shares of Series One, Series Two and Series Three convertible preferred stock into an aggregate of 6,700,487 shares of a new series of Series Five junior preferred stock (Series Five). In addition, the Company issued an aggregate of 2,527,675 shares of Series One and Series Two convertible preferred stock upon the exercise of the warrants issued in connection with the bridge loan that were immediately exchanged for 2,095,515 shares of Series Five during the 2013 recapitalization.
	The Company accounted for the 2013 recapitalization as an extinguishment of its Series One, Series Two and Series Three convertible preferred stock and recorded the Series Five shares at their fair value as of the recapitalization date. In accordance with authoritative accounting guidance, the Company recorded a gain attributable to the common stockholders on the extinguishment of the Series One, Series Two and Series Three convertible preferred stock. The gain of approximately $3.4 million represents the excess of the Series One, Series Two and Series Three convertible preferred stock over the fair value of the shares Series Five issued in connection with the recapitalization.
	Valuation—The value of the Company was estimated using the PWERM. The PWERM considered the most significant near-term driver of value for the Company as the Company's ability to complete a Phase 3 clinical trial of ataluren for the treatment of Duchenne muscular dystrophy caused by nonsense mutations (nmDMD). The remaining scenarios in the PWERM related to funding the completion of the Phase 3 clinical trial for nmDMD. The path to raising this money made up the remaining nodes in the PWERM.
	After identifying the various potential liquidity scenarios and their likely timing, a pre-money enterprise value was assigned to each scenario based on a combination of management's guidance and recent trends in the capital markets. The resulting enterprise value for each liquidity event was divided by the total shares that would be outstanding under each scenario to arrive at a price per share for the common and preferred classes of stock. Each scenario was then assigned an outcome probability based on management's estimates. The resulting probability weighted share values were then discounted to present value at a rate that reflects general industry risks (but not Company specific risks).
	The rights and preferences of the shares of Series Four and Series Five are as follows:
	Dividends—The holders of Series Four and Series Five, in preference to the holders of common stock, were entitled to noncumulative dividends when and if declared by the Board of Directors.
	Liquidation—Upon the liquidation, dissolution, reorganization or winding-up of the Company, the holders of Series Four would have been entitled to receive, before any distribution or payment was made to any other class of security, an amount equal to the original issuance price, plus all declared, but unpaid, dividends. To the extent there had been excess assets to distribute, the holders of Series Five would have been entitled to receive, before any distribution or payment was made to the holders of the common stock, an amount equal to the stated liquidation preference, plus all declared, but unpaid, dividends. To the extent there had been remaining assets to distribute, the holders of common stock would have been entitled to receive such remaining assets.
	Voting—Each holder of Series Four and Series Five was entitled to cast the number of votes into which such holder's shares would have converted. Except as required by law, holders of common stock had limited voting rights. Additionally, except as required by law, and except in certain enumerated circumstances, holders of Series Four and Series Five would have voted together with the holders of common stock as a single class.
	Conversion—Each share of Series Four and Series Five is convertible at any time at the option of the holder into one share of common stock. These conversion ratios were subject to adjustment for certain dilutive events, including certain types of stock splits or stock dividends or future recapitalizations.
	In May 2013, the Company issued and sold an additional 375,000 shares of Series Four, at a price per share of $12.00, for an aggregate purchase price of $4.5 million.
	Common Stock
	In May 2013, the Company's Board of Directors and stockholders approved an amendment to the Company's certificate of incorporation increasing the number of authorized shares of common stock to 125,000,000.
	Initial Public Offering
	In June 2013, the Company closed the initial public offering of its common stock pursuant to a registration statement on Form S-1, as amended. The Company issued and sold an aggregate of 9,627,800 shares of common stock under the registration statement at a public offering price of $15.00 per share, including 1,255,800 shares pursuant to the exercise by the underwriters of an over-allotment option. The Company received net proceeds from the initial public offering of approximately $131.6 million, after deducting underwriting discounts and commissions and other offering expenses payable by the Company.
	Upon closing the initial public offering, all outstanding shares of the Series Four and Series Five were converted into 14,170,956 shares of common stock.
	Follow-On Offerings
	In February 2014, the Company closed a follow-on public offering of its common stock pursuant to a registration statement on Form S-1, as amended. The Company issued and sold an aggregate of 5,163,265 shares of common stock under the registration statement at a public offering price of $24.50 per share, including 673,469 shares pursuant to the exercise by the underwriters of an over-allotment option. The Company received net proceeds from the follow -on public offering of approximately $118.4 million, after deducting underwriting discounts and commissions and other offering expenses payable by the Company.
	On October 16, 2014, the Company closed an underwritten public offering of its common stock pursuant to a registration statement on Form S-3. The Company issued and sold an aggregate of 3,450,000 shares of common stock under the registration statement at a public offering price of $36.25 per share, including 450,000 shares issued upon exercise by the underwriters of their option to purchase additional shares. The Company received net proceeds of approximately $117.6 million after deducting underwriting discounts and commissions and other offering expenses payable by the Company.
	Warrants
	All of the Company's outstanding warrants are classified as liabilities as of December 31, 2014 and 2013 because they contain non-standard antidilution provisions.
	The following is a summary of the Company's outstanding warrants as of December 31, 2014:
		Warrant		Exercise price		Expiration
		shares
	Common stock		6,250	$	128.00	2017
	Common stock		7,030	$	128.00	2019 and 2020
	Common stock		130	$	2,520.00	2019
	The following is a summary of the Company's outstanding warrants as of December 31, 2013:
		Warrant		Exercise price		Expiration
		shares
	Common stock		1,428	$	128.00	2014
	Common stock		6,250	$	128.00	2017
	Common stock		7,030	$	128.00	2019 and 2020
	Common stock		452	$	2,520.00	2014
	In connection with the 2013 recapitalization, all of the Series Two outstanding warrants became warrants to purchase Series Five. In connection with the Company's initial public offering all of the Series Five outstanding warrants became warrants to purchase common stock.

Earnings_per_share

Earnings per share	12 Months Ended
	Dec. 31, 2014
Earnings per share
Earnings Per Share
	8. Earnings per share
	Basic earnings per share is computed by dividing net income (loss) available to common stockholders by the weighted-average number of common shares outstanding. Diluted earnings per share is computed by dividing net income (loss) available to common stockholders by the weighted-average number of common shares plus the effect of dilutive potential common shares outstanding during the period.
	The Prior Series Preferred outstanding in 2012 (through the date of the recapitalization) as well as the Series One, Series Two and Series Three outstanding during 2012 (subsequent to the recapitalization) participated in earnings of the Company through dividend rights. Accordingly, the Company measured earnings per share based upon the two-class method. Net income attributable to common stockholders excludes $132.6 million for the year ended 2012 for net income attributable to participating securities.
	The diluted earnings per share for the year ended December 31, 2012 exclude the impact of approximately 0.6 million and 1.3 million common stock equivalents, respectively, since the effect of including these securities would be anti-dilutive.
	The following table sets forth the computation of basic and diluted earnings per share for common stockholders:
	Net (loss) income per share
		Year ended December 31
		2014			2013			2012
	Numerator
	Net (loss) income	$	(93,753	)	$	(51,574	)	$	(26,235	)
	Deemed dividend		—			(18,249	)		—
	Gain on exchange of convertible preferred stock in connection with recapitalization		—			3,391			159,954
	Less beneficial conversion charge		—			—			(378	)
	Less net income attributable to participating preferred stock		—			—			(132,610	)
	Net (loss) income attributable to common stockholders	$	(93,753	)	$	(66,432	)	$	731
	Denominator
	Denominator for basic earnings per share		31,565,310			12,829,411			3,328
	Effect of dilutive securities:
	Employee stock options		—			—			—
	Series 3 convertible preferred stock		—			—			13,877
	Denominator for diluted earnings per share		31,565,310			12,829,411			17,205
	Net (loss) income per share:
	Basic	$	(2.97	)	$	(5.18	)	$	219.76
	Diluted	$	(2.97	)	$	(5.18	)	$	42.5

Stock_award_plan

Stock award plan	12 Months Ended
	Dec. 31, 2014
Stock award plan
Stock award plan
	9. Stock award plan
	In 2009, the Company's shareholders approved the 2009 Equity and Long-Term Incentive Plan, which provides for the granting of stock option awards, restricted stock awards, and other stock-based and cash-based awards, subject to certain adjustments and annual increases.
	On March 5, 2013, the Company's Board of Directors approved the 2013 Stock Incentive Plan, which provides for the granting of stock option awards, stock appreciation rights, restricted stock, restricted stock units and other stock-based awards in the aggregate of 739,937 shares of common stock. On March 5, 2013, the Board approved a grant of 735,324 shares of restricted stock and 4,613 stock options. There are no additional shares available for issuance under this plan.
	In May 2013, the Company's Board of Directors and stockholders increased by 2,500,000 the number of shares authorized under the 2009 Equity and Long Term Incentive Plan, which provides for the granting of stock option awards, restricted stock awards, and other stock-based and cash-based awards. There are no additional shares available for issuance under this plan.
	In May 2013, the Company's Board of Directors and stockholders approved the 2013 Long Term Incentive Plan, which became effective upon the closing of the Company's IPO. The 2013 Long Term Incentive Plan provides for the grant of incentive stock options, nonstatutory stock options, restricted stock awards and other stock-based awards. The number of shares of common stock reserved for issuance under the 2013 Long Term Incentive Plan is the sum of (1) 262,044 shares of common stock available for issuance under the Company's 2009 Equity and Long Term Incentive Plan and 2013 Stock Incentive Plan, (2) the number of shares (up to 3,040,444 shares) equal to the sum of the number of shares of common stock subject to outstanding awards under the Company's 1998 Employee, Director and Consultant Stock Option Plan, 2009 Equity and Long Term Incentive Plan and 2013 Stock Incentive Plan that expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by the Company at their original issuance price pursuant to a contractual repurchase right plus (3) an annual increase, to be added on the first day of each fiscal year until the expiration of the 2013 Long Term Incentive Plan, equal to the lowest of 2,500,000 shares of common stock, 4% of the number of shares of common stock outstanding on the first day of the fiscal year and an amount determined by the Company's Board of Directors. As of December 31, 2014, awards for 255,463 shares of common stock are available for issuance.
	The Board of Directors has the authority to select the individuals to whom options are granted and determine the terms of each option, including (i) the number of shares of common stock subject to the option; (ii) the date on which the option becomes exercisable; (iii) the option exercise price, which, in the case of incentive stock options, must be at least 100% (110% in the case of incentive stock options granted to a stockholder owning in excess of 10% of the Company's stock) of the fair market value of the common stock as of the date of grant; and (iv) the duration of the option (which, in the case of incentive stock options, may not exceed ten years). Options typically vest over a three- or four-year period.
	Inducement stock option awards
	Pursuant to the NASDAQ inducement grant exception, during the year ended December 31, 2014, the Company issued options to purchase an aggregate of 595,300 shares of common stock to certain new hire employees at a weighted-average exercise price of $37.15 per share. An aggregate of 5,900 of these options were forfeited during the year ended December 31, 2014 in connection with employee separations from the company.
	A summary of stock option activity is as follows:
		Number			Exercise price		Weighted-			Weighted-			Aggregate
		of options					average			average			intrinsic
							exercise			remaining			value
							price			contractual
										term
													(in thousands)
	Outstanding at December 31, 2011		46,794		$226.80 - $1,149.60		$	532.8			5.74 years
	Granted		5,715		$218.40		$	218.4
	Exercised		—
	Forfeited		(10,115	)	$218.40 - $1,149.60		$	604.8
	Outstanding at December 31, 2012		42,394		$218.40 - $1,149.60		$	474			5.02 years
	Granted		2,117,113		$10.59 - $20.76		$	11.29
	Exercised		—
	Forfeited		(63,915	)	$10.85 - $1,149.60		$	12.57
	Outstanding at December 31, 2013		2,095,592		$10.59 - $1,149.60		$	20.24			9.29 years
	Granted		1,639,996		$18.78 - $50.45		$	31.09
	Exercised		(108,645	)	$10.85 - $20.71		$	11
	Forfeited		(193,971	)	$10.85 - $1,149.60		$	32.91
	Outstanding at December 31, 2014		3,432,972		$10.59 - $1,149.60		$	25			8.77 years		$	106,796
	Vested or expected to vest at December 31, 2014		3,239,515				$	24.15			8.78 years		$	101,391
	Exercisable at December 31, 2014		764,277				$	31.84			8.24 years		$	29,809
	There were no stock option exercises in 2012 or 2013.
	The fair value of grants made in the years ended December 31, 2014, 2013 and 2012 was contemporaneously estimated on the date of grant using the following assumptions:
		2014		2013		2012
	Risk-free interest rate	0.11 - 2.04%		0.85 - 1.90%		1.14%
	Expected volatility	70 - 91%		87 - 89%		87%
	Expected term	5.50 - 6.25 years		6.00 - 6.25 years		6.00 - 6.25 years
	The Company assumed no expected dividends for all grants. The weighted average grant date fair value of options granted during the years ended December 31, 2014, 2013 and 2012 was $22.39, $8.23, and $160.65, respectively.
	The Company uses the "simplified method" to determine the expected term of options. Under this method, the expected term represents the average of the vesting period and the contractual term. The expected volatility of share options was estimated based on a historical volatility analysis of peers that were similar to the Company with respect to industry, stage of life cycle, size, and financial leverage. The risk-free rate of the option is based on U.S. Government Securities Treasury Constant Maturities yields at the date of grant for a term similar to the expected term of the option.
	The following table summarizes stock options outstanding and exercisable at December 31, 2014:
		Outstanding									Exercisable
	Range of Exercise Price	Number			Weighted-			Weighted-Average			Number			Weighted
		of Options			Average			Remaining			of Options			Average
					Exercise			Contractual						Exercise
					Price			Life (in years)						Price
	$10.59 - $10.85		1,752,630		$	10.85			8.37			704,958		$	10.85
	$10.85 - $20.76		114,425		$	19.42			8.90			28,675		$	19.72
	$20.76 - $27.05		982,796		$	26.91			9.12			350		$	27.05
	$27.05 - $50.45		554,400		$	39.25			9.62			2,968		$	40.45
	$50.45 - $1,149.60		28,721		$	569.97			4.32			27,326		$	585.05
			3,432,972									764,277
	In December 2013, the Compensation Committee of the Board of Directors modified the terms of stock options granted to executive management. Under the modified terms, the Committee waived all remaining performance conditions associated with the initial vesting of the options such that the options vest with service only conditions. The Company accounted for the modification to the option grants pursuant to ASC Topic 718-20-35 and recognized approximately $0.6 million as additional compensation that was charged to operations during the period ended December 31, 2013.
	In 2014, the Company modified the terms of stock options granted to a departing member of the executive team. The Company accounted for the modification to the option grants pursuant to ASC Topic 718-20-35 and recognized approximately $1.9 million as additional compensation that was charged to operations during the year ended December 31, 2014.
	Restricted Stock Awards—Restricted stock awards are granted subject to certain restrictions, including in some cases service conditions (restricted stock). The grant-date fair value of restricted stock awards, which has been determined based upon the market value of the Company's shares on the grant date, is expensed over the vesting period.
	The following table summarizes information on the Company's restricted stock:
		Restricted Stock
		Number			Weighted
		of Shares			Average
					Grant Date
					Fair Value
	January 1, 2014		1,110,226		$	10.68
	Granted		—			—
	Vested		(373,200	)	$	10.59
	Forfeited		(18,626	)	$	10.75
Unvested at December 31, 2014		718,400		$	10.72
The Company recorded share-based compensation expense in the statement of operations as follows:
	Year ended December 31,
	2014			2013			2012
Research and development	$	9,739		$	4,312		$	1,269
Selling, general and administrative		9,571			4,115			1,020
Total	$	19,310		$	8,427		$	2,289
As of December 31, 2014, there was approximately $38.4 million of total unrecognized compensation cost related to unvested share-based compensation arrangements granted under the Company's Plans. This cost is expected to be recognized as compensation expense over the weighted average remaining service period of approximately 2.66 years.

Other_comprehensive_income_los

Other comprehensive income (loss) and accumulated other comprehensive items	12 Months Ended
	Dec. 31, 2014
Other comprehensive income (loss) and accumulated other comprehensive items
Other comprehensive income (loss) and accumulated other comprehensive items
	10. Other comprehensive income (loss) and accumulated other comprehensive items
	Other comprehensive income (loss) includes changes in equity that are excluded from net loss, such as unrealized gains and losses on marketable securities.
	The following table summarizes other comprehensive income (loss) and the changes in accumulated other comprehensive items, by component, for the years ended December 31, 2014, 2013, and 2012, respectively.
		Unrealized			Foreign			Total
		Gains On			Currency			Accumulated
		Marketable			Translation			Other
		Securities						Comprehensive
								Items
	Balance at December, 2011	$	—		$	—		$	—
	Other comprehensive income/(loss) before reclassifications		—			—			—
	Amounts reclassified from other comprehensive items		—			—			—
	Other comprehensive income/(loss)		—			—			—
	Balance at December 31, 2012	$	—		$	—		$	—
	Other comprehensive income before reclassifications		70			—			70
	Amounts reclassified from other comprehensive items		—			—			—
	Other comprehensive income		70			—			70
	Balance at December 31, 2013	$	70		$	—		$	70
	Other comprehensive loss before reclassifications		(457	)		(350	)		(807	)
	Amounts reclassified from other comprehensive items		—			—			—
	Other comprehensive loss		(387	)		(350	)		(737	)
	Balance at December 31, 2014	$	(387	)	$	(350	)	$	(737	)

Collaborations_and_grants

Collaborations and grants	12 Months Ended
	Dec. 31, 2014
Collaborations and grants
Collaborations and grants
	11. Collaborations and grants
	The Company has ongoing collaborations with the Spinal Muscular Atrophy Foundation (SMA Foundation) and F. Hoffman-La Roche Ltd and Hoffman-La Roche Inc. (collectively, Roche) and early stage discovery arrangements with other institutions. The following are the key terms to the Company's (i) ongoing collaborations and (ii) early stage discovery and development arrangements.
	Roche and SMA Foundation
	In November 2011, the Company and the SMA Foundation entered into a licensing and collaboration agreement with Roche for a spinal muscular atrophy program. Under the terms of the agreement, Roche acquired an exclusive worldwide license to the Company's spinal muscular atrophy program, which includes three compounds currently in preclinical development, as well as potential back-up compounds. The Company received a nonrefundable upfront cash payment of $30.0 million during the research term, which was terminated effective December 31, 2014, Roche provided us with funding, based on an agreed-upon full-time equivalent rate, for an agreed-upon number of full-time equivalent employees that we contributed to the research program.
	The Company applied the multiple element revenue recognition guidance in evaluating the accounting treatment of this collaboration agreement. The Company identified two possible significant deliverables in the collaboration agreement, the license and the research activities. The Company evaluated whether these significant deliverables have stand-alone value and determined that the license does not have standalone value without the ongoing research and development services given the unique nature of the technology. As such, both of these elements were combined as a single unit for accounting purposes. As a result, the Company deferred the $30.0 million upfront payment which was recognized over the estimated performance period of two years, which was the contracted research period. For the years ended December 31, 2014, 2013 and 2012, the Company recognized approximately $20.2 million, $26.6 million and $18.4 million respectively, in collaboration revenue. The balance of the remaining deferred upfront payment was fully recognized as of December 31, 2013.
	Under the agreement, the Company is eligible to receive additional payments from Roche if specified events are achieved with respect to each licensed product, including up to $135 million in research and development event milestones, up to $325 million in sales milestones upon achievement of sales events, and up to double digit royalties on worldwide annual net sales of a commercial product.
	The Company considers that each of the potential milestone events under the agreement would be substantive because the applicable criteria of its revenue recognition policy (see Note 2) would be satisfied.
	In January 2014, the Company announced the initiation of a Phase 1 clinical program in its spinal muscular atrophy collaboration with Roche and the SMA Foundation which triggered a $7.5 million milestone payment from Roche. The Company considered this milestone event substantive because the applicable criteria of its revenue recognition policy would be satisfied and recorded it as collaboration revenue for the year ended December 31, 2014.
	In November 2014, the Company announced the initiation of a Phase 2 study in adult and pediatric patients in its spinal muscular atrophy collaboration with Roche and the SMA Foundation which triggered a $10 million payment from Roche. The Company considered this milestone event substantive because the applicable criteria of its revenue recognition policy would be satisfied and recorded it as collaboration revenue for the year ended December 31, 2014.
	Early stage collaboration and discovery agreements
	From time to time, the Company has arrangements with several organizations pursuant to which the Company uses its discovery technologies to help identify potential drug candidates. The Company does not take ownership of the potential compounds, but rather provides research services to the collaborator using its specialized technology platform.
	Generally, these arrangements are structured such that the collaborator and the Company work together to jointly select targets from which to apply its discovery technologies. The research period for the Company to apply its technology is generally three to four years. The Company will typically receive a nonrefundable, upfront cash payment and the collaborator agrees to provide funding for research activities performed on its behalf.
	The Company applies multiple element revenue recognition guidance in evaluating the accounting treatment for these arrangements. Generally, the two significant deliverables in these arrangements are the license and the research activities. The Company evaluates whether the deliverables have standalone value. Since the Company's discovery technologies are highly specialized, the Company has generally determined that the license does not have standalone value without the ongoing research and development services and generally accounts for these arrangements as a single unit of accounting.
	As a result, the Company has deferred revenue of $1.8 million and $0.9 million as of December 31, 2014 and 2013, respectively, related to these arrangements. For the years ended December 31, 2014 and 2013, the Company recognized approximately $1.3 million and $4.8 million in collaboration revenue, respectively.
	The Company is eligible to receive additional payments from its early stage discovery research arrangements if the discovery compounds are ultimately developed and commercialized. The aggregate potential payments the Company is eligible for if all products are developed is $143 million and up to $252 million in sales milestones upon achievement of specified sales events and up to double digit royalties on worldwide annual net sales of the licensed product.
	The Company considers that each of the potential milestone events under the agreement would be substantive because the applicable criteria of its revenue recognition policy (see Note 2) would be satisfied.
	Grant revenue
	The company receives grant funding from various institutions and governmental bodies. The grants are typically for early discovery research, and typically the grant program lasts from two to five years. The Company records revenue as the research activities are performed. If the granting agency provides for an upfront payment, the amount is deferred and recognized as revenue as the expenditures are incurred.

Income_taxes

Income taxes	12 Months Ended
	Dec. 31, 2014
Income taxes
Income taxes
	12. Income taxes
	Income Taxes
	The Income Tax Provision consisted of the following for the years ended December 31, 2014 and December 31, 2013:
		2014			2013
	Current:
	U.S. Federal	$	—		$	—
	U.S. State and Local		(4,890	)		2
	Foreign		197			—
		$	(4,693	)	$	2
	A reconciliation of the U.S. statutory income tax rate to the Company's effective tax rate is as follows:
					December 31,
		2014			2013			2012
	Federal income tax (benefit) at statutory rate		34	%		34	%		34	%
	State income tax benefit, net of federal benefit		(1.60	)		5.65			3.8
	Permanent differences		(0.93	)		(5.90	)		—
	NOL IRC Section 382 Limitations		(21.53	)		—			—
	Research and development		3.78			15.88			—
	Increase to valuation allowance		9.17			(49.63	)		(35.80	)
	Foreign Taxes		(18.14	)		—			—
	Other		0.01			—			(2.00	)
	Effective income tax rate		4.76	%		0	%		0	%
	The significant components of the Company's deferred tax assets and liabilities at December 31, 2014 and 2013 are as follows:
		2014			2013
	Current:
	Accrued Expense	$	611		$	333
	Deferred tax assets:
	Amortization		69			80
	Depreciation		2,268			1,922
	Deferred revenue		699			350
	Federal tax credits		17,807			14,082
	State tax credits		1,274			1,587
	Federal net operating losses		76,933			88,188
	State net operating losses		9,185			10,457
	Capitalized research and development costs		10,585			12,254
	Other		3,852			3,212
	Total gross deferred tax assets		123,283			132,465
	Less valuation allowance		(123,283	)		(132,465	)
	Net deferred tax assets	$	—		$	—
	At December 31, 2014 and 2013, the Company recorded a full valuation allowance against its net deferred tax assets of approximately $123.3 million and $132.5 million, respectively. The change in the valuation allowance during the years ended December 31, 2014 and 2013 was approximately $9.2 million and $25.6 million, respectively. A full valuation allowance has been recorded since, in the judgment of management, these assets are not more likely than not to be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during periods in which those temporary differences and carryforwards become deductible or are utilized.
	As of December 31, 2014, the Company has approximately $226.3 million and $154.6 million of federal and state net operating loss carryforwards, respectively. As of December 31, 2014, credit carryforwards for federal and state purposes are approximately $6.5 million and $1.7 million, respectively. In addition the Orphan Drug Credit Carryover available as of December 31, 2013 is approximately $11.4 million. The federal net operating loss carryforwards begin to expire in 2021, while the federal credit carryforwards begin to expire in 2019. State net operating loss carryforwards begin to expire in 2030, and the state credit carryforwards begin to expire in 2015. Sections 382 and 383 of the Internal Revenue Code of 1986 subject the future utilization of net operating losses and certain other tax attributes, such as research and experimental tax credits, to an annual limitation in the event of certain ownership changes, as defined. The Company has undergone an ownership change and has determined that a "change in ownership" as defined by IRC Section 382 of the Internal Revenue Code of 1986, as amended, and the rules and regulations promulgated thereunder, did occur in June of 2013. Accordingly, about $231.5 million of the Company's NOL carryforwards are limited and the Company can only use $16.7 million for the first five years from the ownership change and $5.7 million per year going forward. Therefore, $169.2 million of the NOL's will be freed up over the next 20 years and $62.3 million are expected to expire unused which are not included in the deferred tax assets listed above. In summary, there are $226.1 million of NOLs available, out of which $169.2 million are limited by IRC Section 382. At December 31, 2014, there is $82.1 million available for immediate use and an additional $16.7 million will free up in 2015.
	The State of New Jersey provides the Technology Business Tax Certificate Transfer Program enabling approved unprofitable biotechnology businesses to sell their unused net operating loss carryforwards to unaffiliated, profitable corporate taxpayers in the State of New Jersey for cash. The Company has participated in this program and sold state net operating losses and research and development credits totaling $50.4 million during 2014. The New Jersey net operating losses and research and development credits sold during 2014 were generated in 2007 through 2010. The Company recognized a tax benefit of $4.9 million for the year ended December 31, 2014. The company did not participate in this program during the year ended December 31, 2013.
	The income tax benefit for the years ended December 31, 2013 and 2014 differed from the amounts computed by applying the U.S. federal income tax rate of 34% to loss before tax benefit as a result of nondeductible expenses, tax credits generated, utilization of net operating loss carryforwards, and increases in the Company's valuation allowance. The Company applies the elements of FASB ASC 740-10 "Income Taxes—Overall" regarding accounting for uncertainty in income taxes. This clarifies the accounting for uncertainty in income taxes recognized in financial statements and required impact of a tax position to be recognized in the financial statements if that position is more likely than not of being sustained by the taxing authority. As of December 31, 2014 the company did not have any unrecognized tax benefits and has not accrued any interest or penalties through 2014. The Company does not expect to have any unrecognized tax benefits within the next twelve months. The Company's policy is to recognize interest and penalties related to tax matters within the income tax provision. Tax years beginning in 2011 are generally subject to examination by taxing authorities, although net operating losses from all years are subject to examinations and adjustments for at least three years following the year in which the attributes are used.
	For all years through December 31, 2014, the Company generated research credits but has not conducted a study to document the qualified activities. This study may result in an adjustment to the Company's research and development credit carryforwards; however, until a study is completed and any adjustment is known, no amounts are being presented as an uncertain tax position for the last two years. A full valuation allowance has been provided against the Company's research and development credits and, if an adjustment is required, this adjustment would be offset by an adjustment to the deferred tax asset established for the research and development credit carryforwards and the valuation allowance.
	In July 2013, the FASB issued amended guidance for the presentation of an unrecognized tax benefit when a net operating loss carry forward exits, which is effective for the Company January 1, 2014. This amended guidance requires an entity to present an unrecognized tax benefit as a reduction of a deferred tax asset for a net operating carry forward, a similiar tax loss or a tax credit carry forward. If an applicable deferred tax asset is not available or a company does not expect to use the applicable deferred tax asset, the unrecognized tax benefit should be presented as a liability in the financial statements and should not be combined wth an unrelated deferred tax asset. The Company does not expect the adoption of this amended guidance to have a significant impact on the consolidated financial statements.

Commitments_and_contingencies

Commitments and contingencies	12 Months Ended
	Dec. 31, 2014
Commitments and contingencies
Commitments and contingencies
	13. Commitments and contingencies
	Operating leases
	The Company leases office space under a noncancelable operating lease through February 2019. Rent expense was approximately $0.9 million for the years ended December 31, 2014, and $0.7 million for the years ended 2013 and 2012. The Company also leases certain office equipment under operating leases. Future minimum lease payments as of December 31, 2014 are as follows:
	2015	$	1,268
	2016		932
	2017		923
	2018		1,035
	2019		176
	Thereafter		—
		$	4,334
	Other contingencies
	Under various agreements, the Company will be required to pay royalties and milestone payments upon the successful development and commercialization of products. The Company has entered into funding agreements with The Wellcome Trust Limited (Wellcome Trust) for the research and development of small molecule compounds. To the extent that the Company develops and commercializes program intellectual property on a for-profit basis, it may become obligated to pay to Wellcome Trust development and regulatory milestone payments of up to an aggregate of $68.9 million and single-digit royalties on sales of any research program product. The Company's obligation to pay such royalties would continue on a country-by-country basis until the longer of the expiration of the last patent in the program intellectual property in such country covering the research program product and the expiration of market exclusivity of such product in such country.
	The Company has also entered into a collaboration agreement with the SMA Foundation. The Company may become obligated to pay the SMA Foundation single-digit royalties on worldwide net product sales of any collaboration product that we successfully develop and subsequently commercialize or, if we outlicense rights to a collaboration product, a specified percentage of certain payments we receive from our licensee. The Company is not obligated to make such payments unless and until annual sales of a collaboration product exceed a designated threshold. The Company's obligation to make such payments would end upon our payment to the SMA Foundation of a specified amount.
	The Company has employment agreements with certain employees which require the funding of a specific level of payments, if certain events, such as a change in control or termination without cause, occur.

Geographic_Segments

Geographic Segments	12 Months Ended
	Dec. 31, 2014
Geographic Segments
Geographic segments
	14. Geographic Segments
	The Company views its operations and manages its business in one operating segment. The following table presents financial information based on the geographic location of the facilities of the company as of and for the years ended:
		Year ended December 31, 2014
		United States		Non-US		Total
	Total assets	$	330,663	$	2,556	$	333,219
	Property and equipment, net	$	8,555	$	604	$	9,159
	Revenue	$	25,245	$	—	$	25,245
		Year ended December 31, 2013
		United States		Non-US		Total
	Total assets	$	151,903	$	—	$	151,903
	Property and equipment, net	$	6,730	$	—	$	6,730
	Revenue	$	34,696	$	—	$	34,696

401k_plan

401(k) plan	12 Months Ended
	Dec. 31, 2014
401(k) plan
401(k) plan
	15. 401(k) plan
	The Company maintains a 401(k) plan for its employees. Employee contributions are voluntary. The Company may match employee contributions in amounts to be determined at the Company's sole discretion. The Company provides a 33% matching contribution for up to the first 6% of each contributing employee's base salary contributions. The Company made matching contributions to the 401(k) plan and recorded expense of approximately $0.3 million, $0.1 million and $0.2 million for the years ended December 31, 2014, 2013 and 2012, respectively.

Subsequent_events

Subsequent events	12 Months Ended
	Dec. 31, 2014
Subsequent events
Subsequent events
	16. Subsequent events
	The Company has evaluated all events or transactions that occurred after December 31, 2014. In the judgment of management, there were no material events that impacted the consolidated financial statements or disclosures.

Selected_quarterly_financial_d

Selected quarterly financial data	12 Months Ended
	Dec. 31, 2014
Selected quarterly financial data
Selected quarterly financial data
	17. Selected quarterly financial data (Unaudited)
	The following financial information reflects all normal recurring adjustments, which are, in the opinion of management, necessary for a fair statement of the results of the interim periods. Summarized quarterly data for 2014 and 2013 are as follows:
			For the quarters ending
			March 31			June 30			September 30			December 31
	2014:00:00
	Net product sales		$	—		$	—		$	81		$	636
	Collaboration and grant revenue			9,217			1,677			1,613			12,022
	Operating expenses			23,429			27,046			29,295			44,888
	Loss from operations			(14,212	)		(25,369	)		(27,601	)		(32,230	)
	Net loss attributable to common stockholders			(14,098	)		(25,104	)		(27,282	)		(27,269	)
	Basic net loss per common share(1)		$	(0.58	)	$	(0.86	)	$	(0.93	)	$	(0.84	)
	Diluted net loss per common share(1)		$	(0.58	)	$	(0.86	)	$	(0.93	)	$	(0.84	)
	2013:00:00
	Collaboration and grant revenue		$	7,142		$	6,854		$	16,290		$	4,411
	Operating expenses			15,718			21,307			20,565			22,503
	Loss from operations			(8,576	)		(14,453	)		(4,276	)		(18,093	)
	Net loss			(14,685	)		(14,587	)		(4,416	)		(17,886	)
	Deemed dividend			(18,249	)		—			—			—
	Gain on exchange of convertible preferred stock in connection with recapitalization			3,391			—			—			—
	Net income (loss) attributable to common stockholders			(29,543	)		(14,587	)		(4,416	)		(17,886	)
	Basic net income (loss) per common share(1)		$	(6,527.30	)	$	(5.51	)	$	(0.19	)	$	(0.75	)
	Diluted net income (loss) per common share(1)		$	(6,527.30	)	$	(5.51	)	$	(0.19	)	$	(0.75	)
	-1	The amounts were computed independently for each quarter and the sum of the quarters may not total the annual amounts.

Summary_of_significant_account1

Summary of significant accounting policies (Policies)	12 Months Ended
	Dec. 31, 2014
Summary of significant accounting policies
Basis of presentation
	Basis of presentation
	The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) and include all adjustments necessary for the fair presentation of the Company's financial position for the periods presented.
Use of estimates
	Use of estimates
	The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Consolidation
	Consolidation
	The consolidated financial statements include the accounts of PTC Therapeutics, Inc. and our wholly owned subsidiaries. All inter-company accounts, transactions, and profits have been eliminated in consolidation.
Segment and geographic information
	Segment and geographic information
	Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating and reporting segment.
Cash equivalents
	Cash equivalents
	The Company considers all highly liquid investments with a maturity of 90 days or less at the time of purchase to be cash equivalents. Cash equivalents are carried at cost which approximates fair value due to their short-term nature.
Marketable securities
	Marketable securities
	The Company considers securities with original maturities of greater than 90 days to be available for sale securities. Securities under this classification are recorded at fair value and unrealized gains and losses within accumulated other comprehensive income. The estimated fair value of the available for sale securities is determined based on quoted market prices or rates for similar instruments. In addition, the cost of debt securities in this category is adjusted for amortization of premium and accretion of discount to maturity. The Company evaluates securities with unrealized losses to determine whether such losses, if any, are other than temporary.
Fixed assets
	Fixed assets
	Fixed assets are stated at cost. Depreciation is computed starting when the asset is placed into service on a straight-line basis over the estimated useful life of the related asset as follows:
	Leasehold improvements		Lesser of useful life or lease term
	Computer equipment and software		3 years
	Furniture, fixtures, and lab equipment		3 to 7 years
Concentration of credit risks	Concentration of credit risk
	The Company's financial instruments that are exposed to credit risks consist primarily of cash and cash equivalents, available-for-sale marketable securities and accounts receivable. The Company maintains its cash and cash equivalents in bank accounts, which, at times, exceed federally insured limits. The Company has not experienced any credit losses in these accounts and does not believe it is exposed to any significant credit risk on these funds. The Company's investment policy includes guidelines on the quality of the financial institutions and financial instruments the Company is allowed to invest in, which the Company believes minimizes the exposure to concentration of credit risk.
	The Company is subject to credit risk from its accounts receivable related to its product sales revenue of Translarna. The payment terms are predetermined and the Company evaluates the creditworthiness of each customer or distributor on a regular basis. The Company periodically assesses the financial strength of the holders of its accounts receivable to establish allowances for anticipated losses, if necessary. The Company reserves all uninsured amounts billed directly to a patient until the time of cash receipt as collectability is not reasonably assured at the time the product is received. To date, the Company has not incurred any credit losses.
Inventories and cost of product revenue
	Inventories and cost of product revenue
	On August 4, 2014, the Company was notified that the European Commission, or EC, granted conditional marketing authorization for Translarna for the treatment of Duchenne muscular dystrophy caused by nonsense mutations, or nmDMD, in ambulatory patients aged five years and older. The conditional marketing authorization allows the Company to market Translarna in the European Economic Area, or EEA, which is comprised of the 28 member states of the European Union plus Norway, Iceland and Liechtenstein. The conditional marketing authorization is subject to an annual review by the European Medicines Agency, or EMA, and the Company will seek to renew the approval on an annual basis until the Company's obligations have been fulfilled and the approval is converted from a conditional approval into a full approval. The launch in these countries is on a country by country basis. The Company does do not have sufficient history or experience from which to accurately forecast product sales or demand generation. As such, the Company has not capitalized inventory and will not capitalize inventory until full approval has been obtained or until the Company can reasonably predict future product sales. The costs incurred related to the manufacturing of Translarna have been recorded as research and development expense in the statements of operations. The Company's cost of product sales includes royalties and other miscellaneous selling costs, which were not material for the year ended 2014 and therefore included as a component of research and development costs in the current year presentation. The time period over which this inventory is consumed will depend on a number of factors, including the amount of future Translarna sales, and the ability to utilize inventory prior to its expiration date.
Deferred rent
	Deferred rent
	The Company has an operating lease for office space. Rent expense is recorded on a straight-line basis over the initial lease term. The difference between the actual cash paid and the straight-line rent expense is recorded as deferred rent. Leasehold improvements made related to this lease, subsequent to its inception, are amortized over the remaining lease term.
Accumulated other comprehensive income (loss)
	Accumulated other comprehensive income (loss)
	Accumulated other comprehensive income (loss) consists of unrealized gains or losses on marketable securities and foreign currency translation adjustments.
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.
	Net Product Sales
	PTC's net product sales have consisted solely of sales of Translarna for the treatment of DMD caused by nonsense mutations. The Company applies the revenue recognition guidance in accordance with Financial Accounting Standards Board ("FASB") Accounting Standards Codification ("ASC") Subtopic 605-15, Revenue Recognition—Products. The Company recognizes revenue from product sales when there is persuasive evidence that an arrangement exists, title to product and associated risk of loss has passed to the customer, the price is fixed or determinable, collectability is reasonably assured and the Company has no further performance obligations.
	The Company has recorded revenue on sales where Translarna is available on a reimbursed early access program and typically paid for by a government authority or institution. The Company generally recognizes revenue for these named patient or cohort early access programs on a cash basis if all other revenue recognition criteria have been met. Once the Company has established a pattern of collectability, revenue will be recorded upon shipment assuming all other revenue recognition criteria are met.
	The Company records revenue net of estimated discounts and rebates. Allowances are recorded as a reduction of revenue at the time revenues from product sales are recognized. Allowances for government rebates and discounts are established at the time of delivery. These allowances are adjusted to reflect known changes in factors and may impact such allowances in the quarter those changes are known.
	Collaboration and Grant Revenue
	The terms of these agreements typically include payments to the Company of one or more of the following: nonrefundable, upfront license fees; milestone payments; research funding and royalties on future product sales. In addition, the Company generates service revenue through agreements that generally provide for fees for research and development services and may include additional payments upon achievement of specified events.
	The Company evaluates all contingent consideration earned, such as a milestone payment, using the criteria as provided by the Financial Accounting Standards Board (FASB), guidance on the milestone method of revenue recognition. At the inception of a collaboration arrangement, the Company evaluates if milestone payments are substantive. The criteria requires that (1) the Company determines if the milestone is commensurate with either its performance to achieve the milestone or the enhancement of value resulting from our activities to achieve the milestone; (2) the milestone be related to past performance; and (3) 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. The Company recognizes royalties as earned in accordance with the terms of various research and collaboration agreements. If not substantive, the contingent consideration is allocated to the existing units of accounting based on relative selling price and recognized following the same basis previously established for the associated unit of accounting.
	The Company recognizes revenue for reimbursements of research and development costs under collaboration agreements as the services are performed. The Company records these reimbursements as revenue and not as a reduction of research and development expenses as the Company has the risks and rewards as the principal in the research and development activities.
Research and development costs
	Research and development costs
	Research and development expenses include the clinical development costs associated with the Company's product development programs and research and development costs associated with the Company's discovery programs. These expenses include internal research and development costs and the costs of research and development conducted on behalf of the Company by third parties, including sponsored university-based research agreements and clinical study vendors. All research and development costs are expensed as incurred. Costs incurred in obtaining technology licenses are charged immediately to research and development expense if the technology licensed has not reached technological feasibility and has no alternative future uses.
	Nonrefundable advance payments made for goods and services that will be used in future research and development activities are deferred if the contracted party has not yet performed the related activities. The amount deferred is then recognized as expense when the research and development activities are performed. The deferred research and development advance payments were $0.9 million as of December 31, 2014 and not significant as of December 31, 2013.
Fair value of financial instruments
	Fair value of financial instruments
	The Company follows the fair value measurement rules, which provides guidance on the use of fair value in accounting and disclosure for assets and liabilities when such accounting and disclosure is called for by other accounting literature. These rules establish a fair value hierarchy for inputs to be used to measure fair value of financial assets and liabilities. This hierarchy prioritizes the inputs to valuation techniques used to measure fair value into three levels: Level 1 (highest priority), Level 2, and Level 3 (lowest priority).
	•	Level 1—Unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the balance sheet date.
	•	Level 2—Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. Level 2 inputs include quoted prices for similar assets and liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability (i.e., interest rates, yield curves, etc.), and inputs that are derived principally from or corroborated by observable market data by correlation or other means (market corroborated inputs).
	•	Level 3—Inputs are unobservable and reflect the Company's assumptions as to what market participants would use in pricing the asset or liability. The Company develops these inputs based on the best information available.
	Cash equivalents and investments are reflected in the accompanying financial statements at fair value. The carrying amount of receivables and accounts payable and accrued expenses approximates fair value due to the short-term nature of those instruments.
Beneficial conversion
	Beneficial conversion
	When the Company issues a debt or an equity security that is convertible into common stock at a discount from the fair value of the common stock at the date the debt or equity security counterparty is legally committed to purchase such a security (Commitment Date), a beneficial conversion charge is measured and recorded on the Commitment Date for the difference between the fair value of the Company's common stock and the effective conversion price of the convertible debt or equity security. If the intrinsic value of the beneficial conversion feature is greater than the proceeds allocated to the convertible debt or equity security, the amount of the discount assigned to the beneficial conversion feature is limited to the amount of the proceeds allocated to the convertible debt or equity security.
	The amount allocated to the beneficial conversion feature is presented as a discount or reduction to the related debt security or as an immediate charge to earnings available to common shareholders for convertible preferred stock instruments that are convertible by the shareholders at any time. In connection with the Company's recapitalization of its outstanding convertible preferred stock in 2012, the Company recorded a beneficial conversion charge representing the difference between the effective conversion price and the fair value of the Company's common stock as of the Commitment Date. Because the intrinsic value was in excess of the proceeds allocated to the Company's new Series Three convertible preferred stock; the beneficial conversion charge was limited to the allocated proceeds of approximately $0.4 million.
Warrant liability
	Warrant liability
	Warrants to purchase the Company's common stock with nonstandard antidilution provisions, regardless of the probability or likelihood that may conditionally obligate the issuer to ultimately transfer assets, are classified as liabilities and are recorded at their estimated fair value at each reporting period. Any change in fair value of these warrants is recorded as gain/(loss) on warrant valuation each reporting period in Other income/(expense) on the Company's statement of operations.
Impairment of long-lived assets
	Impairment of long-lived assets
	The Company monitors its long-lived assets for indicators of impairment. If such indicators are present, the Company assesses the recoverability of affected assets by determining whether the carrying value of such assets is less than the sum of the undiscounted future cash flows of the assets. If such assets are found not to be recoverable, the Company measures the amount of such impairment by comparing the carrying value of the assets to the fair value of the assets, with the fair value generally determined based on the present value of the expected future cash flows associated with the assets. Although current and historical negative cash flows are indicators of impairment, management believes the future cash flows to be received from the long-lived assets and the potential success of the Company's research programs will exceed the assets' carrying value, and accordingly, the Company believes that no impairment of long-lived assets exists as of December 31, 2014.
Share-based compensation
	Share-based compensation
	The Company measures the cost of employee services received in exchange for an award of equity instruments based on the grant date fair value of the award. Restricted stock awards are measured based on the fair market values of the underlying stock on the dates of grant. For service type awards, share-based compensation expense is recognized on a straight-line basis over the period during which the employee is required to provide service in exchange for the entire award. For awards that vest or begin vesting upon achievement of a performance condition, the Company estimates the likelihood of satisfaction of the performance condition and recognizes compensation expense when achievement of the performance condition is deemed probable using an accelerated attribution model.
	The fair value of options is calculated using the Black-Scholes option pricing model to determine the fair value of stock options on the date of grant based on key assumptions such as expected volatility and expected term. As a new public company, the Company does not have sufficient history to estimate the volatility of its common stock price or the expected life of the options. The Company calculates expected volatility based on reported data for similar publicly traded companies for which historical information is available and will continue to do so until the historical volatility of its common stock is sufficient to measure expected volatility for future option grants.
Income taxes
	Income taxes
	Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and net operating loss and credit carryforwards. Deferred tax assets and liabilities are measured at rates expected to apply to taxable income in the years in which those temporary differences and carryforwards are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in the statement of operations in the period that includes the enactment date. A valuation allowance is recorded when it is not more likely than not that all or a portion of the net deferred tax assets will be realized.
Net tax benefit
	Net tax benefit
	The Company recognized a tax benefit of $4.9 million related to the sale of net operating losses in the New Jersey Technology Business Tax Certificate Transfer Program for the year ended December 31, 2014. We did not participate in this program during the year ended December 31, 2013.
Net (loss) income per share
	Net (loss) income per share
	Basic net income per share is calculated by dividing the net income attributable to common stockholders by the weighted average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net income per share is calculated by dividing the net income attributable to common stockholders by the weighted-average number of common share equivalents outstanding for the period determined using the treasury-stock method and the if-converted method. During periods in which the Company incurs net losses, both basic and diluted loss per share is calculated by dividing the net loss by the weighted average shares outstanding—potentially dilutive securities are excluded from the calculation because their effect would be anti-dilutive. Dilutive common stock equivalents are comprised of convertible preferred stock and options outstanding under the Company's stock option plans.
	In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers. ASU 2014-09 will eliminate transaction- and industry-specific revenue recognition guidance under current GAAP and replace it with a principle-based approach for determining revenue recognition. ASU 2014-09 will require that companies recognize revenue based on the value of transferred goods or services as they occur in the contract. The ASU also will require additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. ASU 2014-09 is effective for annual reporting periods beginning after December 15, 2016. Early application is not permitted. Entities can transition to the standard either retrospectively or as a cumulative-effect adjustment as of the date of adoption. Presently, the Company is assessing what effect the adoption of ASU 2014-09 will have on its financial statements and accompanying notes.

Summary_of_significant_account2

Summary of significant accounting policies (Tables)	12 Months Ended
	Dec. 31, 2014
Summary of significant accounting policies
Schedule of estimated useful life of related assets
	Leasehold improvements	Lesser of useful life or lease term
	Computer equipment and software	3 years
	Furniture, fixtures, and lab equipment	3 to 7 years

Fair_value_of_financial_instru1

Fair value of financial instruments and investments (Tables)	12 Months Ended
	Dec. 31, 2014
Fair value of financial instruments and investments
Schedule of financial assets and liabilities that are required to be measured at fair value on a recurring basis
		December 31, 2014
		Total			Quoted prices		Significant			Significant
					in active		other			unobservable
					markets for		observable			inputs
					identical assets		inputs			(level 3)
					(level 1)		(level 2)
	Marketable securities	$	265,493		$	—	$	265,493		$	—
	Warrant liability	$	188		$	—	$	—		$	188
		December 31, 2013
		Total			Quoted prices		Significant			Significant
					in active		other			unobservable
					markets for		observable			inputs
					identical assets		inputs			(level 3)
					(level 1)		(level 2)
	Marketable securities	$	127,053		$	—	$	127,053		$	—
	Warrant liability	$	58		$	—	$	—		$	58
Summary of marketable securities accounted for as available-for-sale securities
		December 31, 2014
					Gross Unrealized
		Amortized								Fair
		Cost			Gains		Losses			Value
	Corporate debt securities	$	230,379		$	80	$	(428	)	$	230,031
	Government obligations		35,501			7		(46	)		35,462
		$	265,880		$	87	$	(474	)	$	265,493
		December 31, 2013
					Gross Unrealized
		Amortized								Fair
		Cost			Gains		Losses			Value
	Commercial paper	$	14,994		$	4	$	—		$	14,998
	Corporate debt securities		111,989			97		(31	)		112,055
		$	126,983		$	101	$	(31	)	$	127,053
Schedule of marketable securities on the balance sheet
		December 31, 2014
		Less Than			More Than
		12 Months			12 Months
	U.S. corporate debt securities	$	157,758		$	72,273
	Government Obligations		6,003			29,459
	Total Marketable securities	$	163,761		$	101,732
	Marketable securities on the balance sheet at December 31, 2013 matured as follows:
		December 31, 2013
		Less Than			More Than
		12 Months			12 Months
	Commercial paper	$	14,998		$	—
	U.S. corporate debt securities		54,159			57,896
	Total Marketable securities	$	69,157		$	57,896
Summary of changes in the fair value of the Company's Level 3 valuation for warrant liability
		Level 3 assets
	Beginning balance January 1, 2013	$	96
	Change in fair value of warrant liability		(38	)
	Ending balance as of December 31, 2013	$	58
	Change in fair value of warrant liability		130
	Ending balance as of December 31, 2014	$	188

Fixed_assets_Tables

Fixed assets (Tables)	12 Months Ended
	Dec. 31, 2014
Fixed assets
Schedule of fixed assets, net
		December 31,
		2014			2013
	Leasehold improvements	$	13,051		$	12,474
	Computer equipment and software		2,472			2,285
	Furniture, fixtures, and lab equipment		15,070			14,284
	Assets in process		3,483			369
			34,076			29,412
	Less accumulated depreciation and amortization		(24,917	)		(22,682	)
		$	9,159		$	6,730

Accounts_payable_and_accrued_e1

Accounts payable and accrued expenses (Tables)	12 Months Ended
	Dec. 31, 2014
Accounts payable and accrued expenses
Schedule of components of accounts payable and accrued expenses
		December 31,
		2014		2013
	Employee compensation, benefits, and related accruals	$	9,312	$	5,103
	Consulting and contracted research		9,349		4,006
	Professional fees		3,334		1,294
	Accounts payable		4,128		1,124
	Other		2,998		680
		$	29,121	$	12,207

Capital_structure_Tables

Capital structure (Tables)	12 Months Ended
	Dec. 31, 2014
Capital structure
Summary of the Company's outstanding warrants
		Warrant		Exercise price		Expiration
		shares
	Common stock		6,250	$	128.00	2017
	Common stock		7,030	$	128.00	2019 and 2020
	Common stock		130	$	2,520.00	2019
	The following is a summary of the Company's outstanding warrants as of December 31, 2013:
		Warrant		Exercise price		Expiration
		shares
	Common stock		1,428	$	128.00	2014
	Common stock		6,250	$	128.00	2017
	Common stock		7,030	$	128.00	2019 and 2020
	Common stock		452	$	2,520.00	2014

Earnings_per_share_Tables

Earnings per share (Tables)	12 Months Ended
	Dec. 31, 2014
Earnings per share
Schedule of computation of basic and diluted net loss per share for common stockholders
		Year ended December 31
		2014			2013			2012
	Numerator
	Net (loss) income	$	(93,753	)	$	(51,574	)	$	(26,235	)
	Deemed dividend		—			(18,249	)		—
	Gain on exchange of convertible preferred stock in connection with recapitalization		—			3,391			159,954
	Less beneficial conversion charge		—			—			(378	)
	Less net income attributable to participating preferred stock		—			—			(132,610	)
	Net (loss) income attributable to common stockholders	$	(93,753	)	$	(66,432	)	$	731
	Denominator
	Denominator for basic earnings per share		31,565,310			12,829,411			3,328
	Effect of dilutive securities:
	Employee stock options		—			—			—
	Series 3 convertible preferred stock		—			—			13,877
	Denominator for diluted earnings per share		31,565,310			12,829,411			17,205
	Net (loss) income per share:
	Basic	$	(2.97	)	$	(5.18	)	$	219.76
	Diluted	$	(2.97	)	$	(5.18	)	$	42.5

Stock_option_plan_Tables

Stock option plan (Tables)	12 Months Ended
	Dec. 31, 2014
Stock award plan
Summary of stock option activity
		Number			Exercise price		Weighted-			Weighted-			Aggregate
		of options					average			average			intrinsic
							exercise			remaining			value
							price			contractual
										term
													(in thousands)
	Outstanding at December 31, 2011		46,794		$226.80 - $1,149.60		$	532.8			5.74 years
	Granted		5,715		$218.40		$	218.4
	Exercised		—
	Forfeited		(10,115	)	$218.40 - $1,149.60		$	604.8
	Outstanding at December 31, 2012		42,394		$218.40 - $1,149.60		$	474			5.02 years
	Granted		2,117,113		$10.59 - $20.76		$	11.29
	Exercised		—
	Forfeited		(63,915	)	$10.85 - $1,149.60		$	12.57
	Outstanding at December 31, 2013		2,095,592		$10.59 - $1,149.60		$	20.24			9.29 years
	Granted		1,639,996		$18.78 - $50.45		$	31.09
	Exercised		(108,645	)	$10.85 - $20.71		$	11
	Forfeited		(193,971	)	$10.85 - $1,149.60		$	32.91
	Outstanding at December 31, 2014		3,432,972		$10.59 - $1,149.60		$	25			8.77 years		$	106,796
	Vested or expected to vest at December 31, 2014		3,239,515				$	24.15			8.78 years		$	101,391
	Exercisable at December 31, 2014		764,277				$	31.84			8.24 years		$	29,809
Schedule of assumptions used to estimate fair value of grants made on the date of grant
		2014		2013		2012
	Risk-free interest rate	0.11 - 2.04%		0.85 - 1.90%		1.14%
	Expected volatility	70 - 91%		87 - 89%		87%
	Expected term	5.50 - 6.25 years		6.00 - 6.25 years		6.00 - 6.25 years
Summary of stock options outstanding and exercisable
	The following table summarizes stock options outstanding and exercisable at December 31, 2014:
		Outstanding									Exercisable
	Range of Exercise Price	Number			Weighted-			Weighted-Average			Number			Weighted
		of Options			Average			Remaining			of Options			Average
					Exercise			Contractual						Exercise
					Price			Life (in years)						Price
	$10.59 - $10.85		1,752,630		$	10.85			8.37			704,958		$	10.85
	$10.85 - $20.76		114,425		$	19.42			8.90			28,675		$	19.72
	$20.76 - $27.05		982,796		$	26.91			9.12			350		$	27.05
	$27.05 - $50.45		554,400		$	39.25			9.62			2,968		$	40.45
	$50.45 - $1,149.60		28,721		$	569.97			4.32			27,326		$	585.05
			3,432,972									764,277
Summary of information on the Company's restricted stock
		Restricted Stock
		Number			Weighted
		of Shares			Average
					Grant Date
					Fair Value
	January 1, 2014		1,110,226		$	10.68
	Granted		—			—
	Vested		(373,200	)	$	10.59
	Forfeited		(18,626	)	$	10.75
	Unvested at December 31, 2014		718,400		$	10.72
Schedule of share-based compensation expense recorded in the statement of operations
		Year ended December 31,
		2014			2013			2012
	Research and development	$	9,739		$	4,312		$	1,269
	Selling, general and administrative		9,571			4,115			1,020
	Total	$	19,310		$	8,427		$	2,289

Other_comprehensive_income_los1

Other comprehensive income (loss) and accumulated other comprehensive items (Tables)	12 Months Ended
	Dec. 31, 2014
Other comprehensive income (loss) and accumulated other comprehensive items
Summary of other comprehensive income (loss) and the changes in accumulated other comprehensive items
		Unrealized			Foreign			Total
		Gains On			Currency			Accumulated
		Marketable			Translation			Other
		Securities						Comprehensive
								Items
	Balance at December, 2011	$	—		$	—		$	—
	Other comprehensive income/(loss) before reclassifications		—			—			—
	Amounts reclassified from other comprehensive items		—			—			—
	Other comprehensive income/(loss)		—			—			—
	Balance at December 31, 2012	$	—		$	—		$	—
	Other comprehensive income before reclassifications		70			—			70
	Amounts reclassified from other comprehensive items		—			—			—
	Other comprehensive income		70			—			70
	Balance at December 31, 2013	$	70		$	—		$	70
	Other comprehensive loss before reclassifications		(457	)		(350	)		(807	)
	Amounts reclassified from other comprehensive items		—			—			—
	Other comprehensive loss		(387	)		(350	)		(737	)
	Balance at December 31, 2014	$	(387	)	$	(350	)	$	(737	)

Income_taxes_Tables

Income taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income taxes
Components of Income Tax Provision
		2014			2013
	Current:
	U.S. Federal	$	—		$	—
	U.S. State and Local		(4,890	)		2
	Foreign		197			—
		$	(4,693	)	$	2
Schedule of reconciliation of the U.S. statutory income tax rate to the Company's effective tax rate
					December 31,
		2014			2013			2012
	Federal income tax (benefit) at statutory rate		34	%		34	%		34	%
	State income tax benefit, net of federal benefit		(1.60	)		5.65			3.8
	Permanent differences		(0.93	)		(5.90	)		—
	NOL IRC Section 382 Limitations		(21.53	)		—			—
	Research and development		3.78			15.88			—
	Increase to valuation allowance		9.17			(49.63	)		(35.80	)
	Foreign Taxes		(18.14	)		—			—
	Other		0.01			—			(2.00	)
	Effective income tax rate		4.76	%		0	%		0	%
Schedule of significant components of the Company's deferred tax assets and liabilities
		2014			2013
	Current:
	Accrued Expense	$	611		$	333
	Deferred tax assets:
	Amortization		69			80
	Depreciation		2,268			1,922
	Deferred revenue		699			350
	Federal tax credits		17,807			14,082
	State tax credits		1,274			1,587
	Federal net operating losses		76,933			88,188
	State net operating losses		9,185			10,457
	Capitalized research and development costs		10,585			12,254
	Other		3,852			3,212
	Total gross deferred tax assets		123,283			132,465
	Less valuation allowance		(123,283	)		(132,465	)
	Net deferred tax assets	$	—		$	—

Commitments_and_contingencies_

Commitments and contingencies (Tables)	12 Months Ended
	Dec. 31, 2014
Commitments and contingencies
Schedule of future minimum lease payments
	2015	$	1,268
	2016		932
	2017		923
	2018		1,035
	2019		176
	Thereafter		—
		$	4,334

Geographic_segments_Tables

Geographic segments (Tables)	12 Months Ended
	Dec. 31, 2014
Geographic Segments
Summary of financial information based on geographical location
		Year ended December 31, 2014
		United States		Non-US		Total
	Total assets	$	330,663	$	2,556	$	333,219
	Property and equipment, net	$	8,555	$	604	$	9,159
	Revenue	$	25,245	$	—	$	25,245
		Year ended December 31, 2013
		United States		Non-US		Total
	Total assets	$	151,903	$	—	$	151,903
	Property and equipment, net	$	6,730	$	—	$	6,730
	Revenue	$	34,696	$	—	$	34,696

Selected_quarterly_financial_d1

Selected quarterly financial data (Tables)	12 Months Ended
	Dec. 31, 2014
Selected quarterly financial data
Summary of quarterly data
			For the quarters ending
			March 31			June 30			September 30			December 31
	2014:00:00
	Net product sales		$	—		$	—		$	81		$	636
	Collaboration and grant revenue			9,217			1,677			1,613			12,022
	Operating expenses			23,429			27,046			29,295			44,888
	Loss from operations			(14,212	)		(25,369	)		(27,601	)		(32,230	)
	Net loss attributable to common stockholders			(14,098	)		(25,104	)		(27,282	)		(27,269	)
	Basic net loss per common share(1)		$	(0.58	)	$	(0.86	)	$	(0.93	)	$	(0.84	)
	Diluted net loss per common share(1)		$	(0.58	)	$	(0.86	)	$	(0.93	)	$	(0.84	)
	2013:00:00
	Collaboration and grant revenue		$	7,142		$	6,854		$	16,290		$	4,411
	Operating expenses			15,718			21,307			20,565			22,503
	Loss from operations			(8,576	)		(14,453	)		(4,276	)		(18,093	)
	Net loss			(14,685	)		(14,587	)		(4,416	)		(17,886	)
	Deemed dividend			(18,249	)		—			—			—
	Gain on exchange of convertible preferred stock in connection with recapitalization			3,391			—			—			—
	Net income (loss) attributable to common stockholders			(29,543	)		(14,587	)		(4,416	)		(17,886	)
	Basic net income (loss) per common share(1)		$	(6,527.30	)	$	(5.51	)	$	(0.19	)	$	(0.75	)
	Diluted net income (loss) per common share(1)		$	(6,527.30	)	$	(5.51	)	$	(0.19	)	$	(0.75	)
	-1	The amounts were computed independently for each quarter and the sum of the quarters may not total the annual amounts.

The_Company_Details

The Company (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
	item
The Company
Accumulated deficit	$422,551	$328,798
Minimum age of ambulatory patient	5 years
Number of member states of the European Union	31

Summary_of_significant_account3

Summary of significant accounting policies (Details)	12 Months Ended
	Dec. 31, 2014
	item
Segment and geographic information
Number of operating segments	1
Computer equipment and software
Fixed assets
Estimated useful life	3 years
Furniture, fixtures, and lab equipment | Minimum
Fixed assets
Estimated useful life	3 years
Furniture, fixtures, and lab equipment | Maximum
Fixed assets
Estimated useful life	7 years

Summary_of_significant_account4

Summary of significant accounting policies (Details 3) (USD $)	12 Months Ended		0 Months Ended
	Dec. 31, 2014	Dec. 31, 2012	Mar. 07, 2013
Research and development costs
Deferred research and development advance payments	$900,000
Beneficial conversion
Beneficial conversion charge		378,000
Impairment of long-lived assets
Impairment of long-lived assets	0
Income Tax Expense (Benefit), Continuing Operations [Abstract]
Net tax benefit	4,693,000
New Jersey
Income Tax Expense (Benefit), Continuing Operations [Abstract]
Net tax benefit	$4,900,000
Common stock
Reverse Stock Split [Abstract]
Reverse stock split ratio			0.0083

Fair_value_of_financial_instru2

Fair value of financial instruments and investments (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Financial assets and liabilities measured at fair value on recurring basis
Marketable securities	$265,493	$127,053
Recurring basis | Total
Financial assets and liabilities measured at fair value on recurring basis
Marketable securities	265,493	127,053
Warrant liability	188	58
Recurring basis | Significant other observable inputs (level 2)
Financial assets and liabilities measured at fair value on recurring basis
Marketable securities	265,493	127,053
Recurring basis | Significant unobservable inputs (level 3)
Financial assets and liabilities measured at fair value on recurring basis
Warrant liability	$188	$58

Fair_value_of_financial_instru3

Fair value of financial instruments and investments (Details 2) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Fair value of financial instruments and investments
Transfers of assets between Level 1 and Level 2 of the fair value measurement hierarchy	$0
Marketable securities accounted for as available-for-sale securities
Amortized Cost	265,880	126,983
Gross Unrealized Gains	87	101
Gross Unrealized Losses	-474	-31
Total Marketable securities	265,493	127,053
Commercial paper
Marketable securities accounted for as available-for-sale securities
Amortized Cost		14,994
Gross Unrealized Gains		4
Total Marketable securities		14,998
Corporate Debt Securities [Member]
Marketable securities accounted for as available-for-sale securities
Amortized Cost	230,379	111,989
Gross Unrealized Gains	80	97
Gross Unrealized Losses	-428	-31
Total Marketable securities	230,031	112,055
Government Agencies Debt Securities [Member]
Marketable securities accounted for as available-for-sale securities
Amortized Cost	35,501
Gross Unrealized Gains	7
Gross Unrealized Losses	-46
Total Marketable securities	$35,462

Fair_value_of_financial_instru4

Fair value of financial instruments and investments (Details 3) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Marketable securities on the balance sheet
Total Marketable securities, Less Than 12 Months	$163,761	$69,157
Total Marketable securities, More Than 12 Months	101,732	57,896
Commercial paper
Marketable securities on the balance sheet
Total Marketable securities, Less Than 12 Months		14,998
U.S. corporate debt securities
Marketable securities on the balance sheet
Total Marketable securities, Less Than 12 Months	157,758	54,159
Total Marketable securities, More Than 12 Months	72,273	57,896
Government Agencies Debt Securities [Member]
Marketable securities on the balance sheet
Total Marketable securities, Less Than 12 Months	6,003
Total Marketable securities, More Than 12 Months	$29,459

Fair_value_of_financial_instru5

Fair value of financial instruments and investments (Details 4) (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Jun. 30, 2013
Common stock
Assumption used to estimate the fair value of warrant liability by utilizing the Black-Scholes option-pricing model
Fair value of shares (in dollars per share)			$15
Warrant
Changes in the fair value of warrant liability
Beginning balance	$58	$96
Change in fair value of warrant liability	130	-38
Ending balance	$188	$58
Warrant | Minimum
Assumption used to estimate the fair value of warrant liability by utilizing the Black-Scholes option-pricing model
Volatility (as a percent)	68.00%	61.00%
Risk-free interest rate (as a percent)	0.89%	0.07%
Strike price (in dollars per share)	$128	$128
Expected life	2 years 6 months	3 months 18 days
Warrant | Maximum
Assumption used to estimate the fair value of warrant liability by utilizing the Black-Scholes option-pricing model
Volatility (as a percent)	70.00%	89.00%
Risk-free interest rate (as a percent)	1.65%	2.10%
Strike price (in dollars per share)	$2,520	$2,520
Expected life	4 years 8 months 12 days	5 years 8 months 12 days
Warrant | Common stock
Assumption used to estimate the fair value of warrant liability by utilizing the Black-Scholes option-pricing model
Fair value of shares (in dollars per share)	$51.77	$16.97

Fixed_assets_Details

Fixed assets (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fixed assets
Gross fixed assets	$34,076	$29,412
Less accumulated depreciation and amortization	-24,917	-22,682
Net fixed assets	9,159	6,730
Depreciation expense	2,235	2,396	2,704
Leasehold improvements
Fixed assets
Gross fixed assets	13,051	12,474
Computer equipment and software
Fixed assets
Gross fixed assets	2,472	2,285
Furniture, fixtures, and lab equipment
Fixed assets
Gross fixed assets	15,070	14,284
Assets in process
Fixed assets
Gross fixed assets	$3,483	$369

Accounts_payable_and_accrued_e2

Accounts payable and accrued expenses (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Accounts payable and accrued expenses
Employee compensation, benefits, and related accruals	$9,312	$5,103
Consulting and contracted research	9,349	4,006
Professional fees	3,334	1,294
Accounts payable	4,128	1,124
Other	2,998	680
Accounts payable and accrued expenses	$29,121	$12,207

Longterm_debt_Details

Long-term debt (Details) (USD $)	1 Months Ended	12 Months Ended	1 Months Ended
	Jul. 31, 2013	Dec. 31, 2013	Dec. 31, 2010	Sep. 30, 2009
				item
Debt
Paid outstanding principal and interest, due under promissory notes issued	$2,600,000
Gains (Losses) on Extinguishment of Debt		-130,000
Secured debt facility
Debt
Maximum borrowing capacity				25,000,000
Amount borrowed			$10,000,000	$12,500,000
Number of lenders				2

Capital_structure_Details

Capital structure (Details) (USD $)	1 Months Ended	3 Months Ended	12 Months Ended
	Jul. 31, 2012	Mar. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Capital structure
Par value (in dollars per share)					0.001
Number of members of board of directors who can be elected by holders of the preferred stock, voting as a single class					6
Proceeds from Issuance of Convertible Preferred Stock				$29,355,000
Preferred Stock Redemption Discount	160,000,000	3,391,000	3,391,000	159,954,000
Maximum
Capital structure
Shares authorized					156,995,095
Minimum
Capital structure
Percentage of the outstanding preferred shares on an as-converted to common stock basis					66.67%
Series A
Capital structure
Shares authorized					750,000
Conversion factor					0.0833
Liquidation preference (in dollars per share)					1
Aggregate liquidation preference					750,000
Series B
Capital structure
Shares authorized					187,500
Conversion factor					0.1333
Liquidation preference (in dollars per share)					2
Aggregate liquidation preference					375,000
Series C
Capital structure
Shares authorized					6,295,000
Conversion factor					0.1389
Liquidation preference (in dollars per share)					2.5
Aggregate liquidation preference					15,000,000
Series D
Capital structure
Shares authorized					13,769,935
Conversion factor					0.1548
Liquidation preference (in dollars per share)					3.25
Aggregate liquidation preference					42,561,249
Series E
Capital structure
Shares authorized					126,735,022
Conversion factor					0.0548
Liquidation preference (in dollars per share)					0.397644
Aggregate liquidation preference					49,999,998
Series E-2
Capital structure
Shares authorized					3,670,138
Conversion factor					1
Liquidation preference (in dollars per share)					7.26
Aggregate liquidation preference					26,645,187
Series F
Capital structure
Shares authorized					675,000
Conversion factor					1
Liquidation preference (in dollars per share)					16
Aggregate liquidation preference					10,000,000
Series F-2 convertible preferred stock
Capital structure
Shares authorized					1,612,500
Conversion factor					1
Liquidation preference (in dollars per share)					16
Aggregate liquidation preference					24,248,048
Series G
Capital structure
Shares authorized					3,300,000
Conversion factor					1
Liquidation preference (in dollars per share)					16
Aggregate liquidation preference					50,300,000
Series F, F-2 and G | Minimum
Capital structure
Percentage of the outstanding preferred shares on an as-converted to common stock basis					66.67%
Series One convertible preferred stock
Capital structure
Number of members of board of directors who can be elected by holders of the preferred stock, voting as a single class				12
Stock Issued During Period, Shares, New Issues				1,483,337
Proceeds from Issuance of Convertible Preferred Stock				$29,700,000
Original issuance price multiplier				2
Assets available for distribution to series convertible preferred stock, distribution percentage				23.53%
Assets available for distribution to series convertible preferred stock, distribution percentage.				23.53%
Remaining assets distribution percentage				20.00%
Shares issued upon conversion of preferred stock multiplier				5
Convertible Preferred Stock, Shares Issued upon Conversion				2
Series Two convertible preferred stock
Capital structure
Assets available for distribution to series convertible preferred stock, distribution percentage				76.47%
Stated liquidation preference amount multiplier				1
Assets available for distribution to series convertible preferred stock, distribution percentage.				67.65%
Remaining assets distribution percentage				55.00%
Convertible Preferred Stock, Shares Issued upon Conversion				1
Series Three convertible preferred stock
Capital structure
Stated liquidation preference amount multiplier				1
Assets available for distribution to series convertible preferred stock, distribution percentage.				8.82%
Remaining assets distribution percentage				25.00%
Convertible Preferred Stock, Shares Issued upon Conversion				1

Capital_structure_Details_2

Capital structure (Details 2) (USD $)

1 Months Ended

3 Months Ended

12 Months Ended

0 Months Ended

1 Months Ended

0 Months Ended

1 Months Ended

Jul. 31, 2012

Mar. 31, 2014

Mar. 31, 2013

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Mar. 07, 2013

31-May-13

Oct. 16, 2014

Feb. 28, 2014

Jun. 30, 2013

Feb. 28, 2013

Capital structure

Aggregate gross proceeds

$29,355,000

Gross proceeds raised

60,000,000

Gain on extinguishment of shares of Series One, Two and Three stock

160,000,000

3,391,000

3,391,000

159,954,000

Aggregate purchase price

235,979,097

131,649,688

Common stock

Common stock, authorized shares

125,000,000

125,000,000

125,000,000

Series One and Series Two | Warrant

Capital structure

Warrants issued to purchase shares

2,527,675

Exercise price (in dollars per share)

$0.01

Shares issued and sold

2,527,675

Series Four convertible preferred stock

Capital structure

Shares issued and sold

4,497,035

375,000

Aggregate gross proceeds

54,000,000

Share price (in dollars per share)

$12

Aggregate purchase price

4,500,000

Series Five convertible preferred stock

Capital structure

Number of shares issued upon conversion

6,700,487

Common stock

Number of shares issued upon conversion

6,700,487

Series Five convertible preferred stock | Warrant

Capital structure

Number of shares issued upon conversion

2,095,515

Common stock

Number of shares issued upon conversion

2,095,515

Common stock

Capital structure

Shares issued and sold

3,450,000

5,163,265

9,627,800

Reverse stock split ratio

0.0083

Share price (in dollars per share)

$15

Public offering price (in dollars per share)

$36.25

$24.50

Common stock

Common stock shares issuable pursuant to the exercise by the underwriters of an over-allotment option

450,000

673,469

1,255,800

Net proceeds from public offerings

117,600,000

118,400,000

Net proceeds from initial public offering

131,600,000

Series Four and Series Five Convertible Preferred Stock

Capital structure

Number of shares issued upon conversion

14,170,956

Number of shares issuable upon conversion of each stock

1

Common stock

Number of shares issued upon conversion

14,170,956

Convertible promissory notes

Capital structure

Principal amount of convertible promissory notes issued

6,000,000

Debt discount recorded to interest expense

6,000,000

Amount raised in bridge financing

$6,000,000

Convertible promissory notes | Series Four convertible preferred stock

Capital structure

Shares issued upon conversion of convertible promissory notes

502,919

Capital_structure_Details_3

Capital structure (Details 3) (Common stock, USD $)	Dec. 31, 2014	Dec. 31, 2013
2014
Warrants
Warrant shares		1,428
Exercise price (in dollars per share)		$128
2017
Warrants
Warrant shares	6,250	6,250
Exercise price (in dollars per share)	$128	$128
2019 and 2020
Warrants
Warrant shares	7,030	7,030
Exercise price (in dollars per share)	$128	$128
2019
Warrants
Warrant shares	130
Exercise price (in dollars per share)	$2,520
2014
Warrants
Warrant shares		452
Exercise price (in dollars per share)		$2,520

Earnings_per_share_Details

Earnings per share (Details) (USD $)	1 Months Ended	3 Months Ended								12 Months Ended
In Thousands, except Share data, unless otherwise specified	Jul. 31, 2012	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net income (loss) per share
Common stock equivalents excluded from calculation of diluted earnings per share since the effect would be anti-dilutive											600,000	1,300,000
Numerator
Net loss						($17,886)	($4,416)	($14,587)	($14,685)	($93,753)	($51,574)	($26,235)
Deemed dividend									-18,249		-18,249
Gain on exchange of convertible preferred stock in connection with recapitalization	160,000								3,391		3,391	159,954
Less beneficial conversion charge												-378
Less net income attributable to participating preferred stock												-132,610
Net loss attributable to common stockholders										($93,753)	($66,432)	$731
Denominator
Denominator for basic earnings per share (in shares)										31,565,310	12,829,411	3,328
Effect of dilutive securities:
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Preferred Stock												13,877
Denominator for diluted earnings per share (in shares)										31,565,310	12,829,411	17,205
Net loss per share:
Earnings Per Share, Basic		($0.84)	($0.93)	($0.86)	($0.58)	($0.75)	($0.19)	($5.51)	($6,527.30)	($2.97)	($5.18)	$219.76
Earnings Per Share, Diluted		($0.84)	($0.93)	($0.86)	($0.58)	($0.75)	($0.19)	($5.51)	($6,527.30)	($2.97)	($5.18)	$42.50

Stock_option_plan_Details

Stock option plan (Details) (USD $)	12 Months Ended				1 Months Ended	0 Months Ended
	Dec. 31, 2011	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	31-May-13	Mar. 05, 2013
Weighted-average remaining contractual term
Outstanding at the end of the period	5 years 8 months 27 days
Stock option
Number of options
Outstanding at the beginning of the period (in shares)		2,095,592	42,394	46,794
Granted (in shares)		1,639,996	2,117,113	5,715
Exercised (in shares)		-108,645
Forfeited (in shares)		-193,971	-63,915	-10,115
Outstanding at the end of the period (in shares)		3,432,972	2,095,592	42,394
Vested or expected to vest at the end of the period (in shares)		3,239,515
Exercisable at the end of the period (in shares)		764,277
Exercise price
Granted (in dollars per share)				$218.40
Weighted-average exercise price
Outstanding at the beginning of the period (in dollars per share)		$20.24	$474	$532.80
Granted (in dollars per share)		$31.09	$11.29	$218.40
Exercised (in dollars per share)		$11
Forfeited (in dollars per share)		$32.91	$12.57	$604.80
Outstanding at the end of the period (in dollars per share)		$25	$20.24	$474
Vested or expected to vest at the end of the period (in dollars per share)		$24.15
Exercisable at the end of the period (in dollars per share)		$31.84
Weighted-average remaining contractual term
Outstanding at the end of the period		8 years 9 months 7 days	9 years 3 months 15 days	5 years 7 days
Vested or expected to vest at the end of the period		8 years 9 months 11 days
Exercisable at the end of the period		8 years 2 months 27 days
Valuation assumptions
Risk-free interest rate (as a percent)				1.14%
Expected volatility (as a percent)				87.00%
Expected dividend yield (as a percent)		0.00%	0.00%	0.00%
Weighted average grant date fair value (in dollars per share)		$22.39	$8.23	$160.65
Aggregate intrinsic value
Outstanding at the end of the period (in dollars)		$106,796
Vested or expected to vest at the end of the period (in dollars)		101,391
Exercisable at the end of the period (in dollars)		$29,809
Stock option | Minimum
Stock option plan
Vesting period		3 years
Exercise price
Outstanding at the beginning of the period (in dollars per share)		$10.59	$218.40	$226.80
Granted (in dollars per share)		$18.78	$10.59
Exercised (in dollars per share)		$10.85
Forfeited (in dollars per share)		$10.85	$10.85	$218.40
Outstanding at the end of the period (in dollars per share)		$10.59	$10.59	$218.40
Valuation assumptions
Risk-free interest rate (as a percent)		0.11%	0.85%
Expected volatility (as a percent)		70.00%	87.00%
Expected term		5 years 6 months	6 years	6 years
Stock option | Maximum
Stock option plan
Vesting period		4 years
Exercise price
Outstanding at the beginning of the period (in dollars per share)		$1,149.60	$1,149.60	$1,149.60
Granted (in dollars per share)		$50.45	$20.76
Exercised (in dollars per share)		$20.71
Forfeited (in dollars per share)		$1,149.60	$1,149.60	$1,149.60
Outstanding at the end of the period (in dollars per share)		$1,149.60	$1,149.60	$1,149.60
Valuation assumptions
Risk-free interest rate (as a percent)		2.04%	1.90%
Expected volatility (as a percent)		91.00%	89.00%
Expected term		6 years 3 months	6 years 3 months	6 years 3 months
2009 Equity and Long-Term Incentive Plan
Stock option plan
Number of shares available for issuance					0
Number of additional shares authorized					2,500,000
2009 Equity and Long-Term Incentive Plan | Stock option | Minimum
Stock option plan
Stock options granted, exercise price as percentage of the fair market value of common stock at grant date		100.00%
Stock options granted to stockholder with specified ownership percentage, exercise price as percentage of the fair market value of common stock at grant date		110.00%
Stockholder's specified ownership percentage		10.00%
2009 Equity and Long-Term Incentive Plan | Stock option | Maximum
Stock option plan
Expiration period		10 years
2013 Stock Incentive Plan
Stock option plan
Number of shares available for issuance						0
2013 Stock Incentive Plan | Stock option
Stock option plan
Number of shares of restricted stock granted						4,613
2013 Stock Incentive Plan | Restricted stock
Stock option plan
Number of shares of restricted stock granted						735,324
2013 Stock Incentive Plan | Common stock
Stock option plan
Number of shares authorized						739,937
2009 Equity and Long Term Incentive Plan and 2013 Stock Incentive Plan | Common stock
Stock option plan
Number of shares available for issuance					262,044
2013 Long Term Incentive Plan | Common stock
Stock option plan
Number of shares available for issuance		255,463
2013 Long Term Incentive Plan | Common stock | Minimum
Stock option plan
Annual increase in the number of shares on the first day of the fiscal year					2,500,000
Annual increase in the number of shares outstanding on the first day of the fiscal year (as a percent)					4.00%
2013 Long Term Incentive Plan | Common stock | Maximum
Stock option plan
Number of shares subject to outstanding awards					3,040,444
Inducement grant plan | Stock option
Number of options
Granted (in shares)		595,300
Forfeited (in shares)		-5,900
Exercise price
Granted (in dollars per share)		$37.15

Stock_option_plan_Details_2

Stock option plan (Details 2) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Stock options outstanding and exercisable
Outstanding, Number of options (in shares)	3,432,972
Exercisable, Number of options (in shares)	764,277
Additional compensation recognized due to modifications to the options granted	$1.90	$0.60
$10.59-$10.85
Stock options outstanding and exercisable
Range of Exercise Price, Lower (in dollars per share)	$10.59
Range of Exercise Price, Higher (in dollars per share)	$10.85
Outstanding, Number of options (in shares)	1,752,630
Outstanding, Weighted-Average Exercise Price (in dollars per share)	$10.85
Outstanding, Weighted-Average Remaining Contractual Life	8 years 4 months 13 days
Exercisable, Number of options (in shares)	704,958
Exercisable, Weighted-Average Exercise Price (in dollars per share)	$10.85
$10.85-$20.76
Stock options outstanding and exercisable
Range of Exercise Price, Lower (in dollars per share)	$10.85
Range of Exercise Price, Higher (in dollars per share)	$20.76
Outstanding, Number of options (in shares)	114,425
Outstanding, Weighted-Average Exercise Price (in dollars per share)	$19.42
Outstanding, Weighted-Average Remaining Contractual Life	8 years 10 months 24 days
Exercisable, Number of options (in shares)	28,675
Exercisable, Weighted-Average Exercise Price (in dollars per share)	$19.72
$20.76 - $490.80
Stock options outstanding and exercisable
Range of Exercise Price, Lower (in dollars per share)	$20.76
Range of Exercise Price, Higher (in dollars per share)	$27.05
Outstanding, Number of options (in shares)	982,796
Outstanding, Weighted-Average Exercise Price (in dollars per share)	$26.91
Outstanding, Weighted-Average Remaining Contractual Life	9 years 1 month 13 days
Exercisable, Number of options (in shares)	350
Exercisable, Weighted-Average Exercise Price (in dollars per share)	$27.05
$490.80-735.60
Stock options outstanding and exercisable
Range of Exercise Price, Lower (in dollars per share)	$27.05
Range of Exercise Price, Higher (in dollars per share)	$50.45
Outstanding, Number of options (in shares)	554,400
Outstanding, Weighted-Average Exercise Price (in dollars per share)	$39.25
Outstanding, Weighted-Average Remaining Contractual Life	9 years 7 months 13 days
Exercisable, Number of options (in shares)	2,968
Exercisable, Weighted-Average Exercise Price (in dollars per share)	$40.45
$1,149.60
Stock options outstanding and exercisable
Range of Exercise Price, Lower (in dollars per share)	$50.45
Range of Exercise Price, Higher (in dollars per share)	$1,149.60
Outstanding, Number of options (in shares)	28,721
Outstanding, Weighted-Average Exercise Price (in dollars per share)	$569.97
Outstanding, Weighted-Average Remaining Contractual Life	4 years 3 months 26 days
Exercisable, Number of options (in shares)	27,326
Exercisable, Weighted-Average Exercise Price (in dollars per share)	$585.05

Stock_option_plan_Details_3

Stock option plan (Details 3) (Restricted stock, USD $)	12 Months Ended
	Dec. 31, 2014
Restricted stock
Number of Shares
Balance at the beginning of the period (in shares)	1,110,226
Vested (in shares)	-373,200
Forfeited (in shares)	-18,626
Balance at the end of the period (in shares)	718,400
Weighted Average Grant Date Fair Value
Balance at the beginning of the period (in dollars per share)	$10.68
Vested	$10.59
Forfeited (in dollars per share)	$10.75
Balance at the end of the period (in dollars per share)	$10.72

Stock_option_plan_Details_4

Stock option plan (Details 4) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based compensation expense recorded in the statement of operations
Share-based compensation expense	$19,310,000	$8,427,000	$2,289,000
Unrecognized compensation cost	38,400,000
Weighted average remaining service period for recognition of unrecognized compensation cost	2 years 7 months 28 days
Research and development
Share-based compensation expense recorded in the statement of operations
Share-based compensation expense	9,739,000	4,312,000	1,269,000
Selling, general and administrative
Share-based compensation expense recorded in the statement of operations
Share-based compensation expense	$9,571,000	$4,115,000	$1,020,000

Other_comprehensive_income_los2

Other comprehensive income (loss) and accumulated other comprehensive items (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Other comprehensive income and accumulated other comprehensive items
Balance at the beginning of the period	$70
Other comprehensive income/(losses) before reclassifications	-807	70
Other comprehensive income/(loss)	-737	70
Balance at the end of the period	-737	70
Unrealized Gains/(Losses) On Marketable Securities
Other comprehensive income and accumulated other comprehensive items
Balance at the beginning of the period	70
Other comprehensive income/(losses) before reclassifications	-457	70
Other comprehensive income/(loss)	-387	70
Balance at the end of the period	-387	70
Foreign Currency Gain (Loss) [Member]
Other comprehensive income and accumulated other comprehensive items
Other comprehensive income/(losses) before reclassifications	-350
Other comprehensive income/(loss)	-350
Balance at the end of the period	($350)

Collaborations_and_grants_Deta

Collaborations and grants (Details) (USD $)	12 Months Ended	1 Months Ended			12 Months Ended		0 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Nov. 30, 2014	Jan. 31, 2014	Nov. 30, 2011	Dec. 31, 2013	Dec. 31, 2012	Jan. 02, 2011
				item			item
Minimum
Grant revenue
Term of grant program	2 years
Maximum
Grant revenue
Term of grant program	5 years
Collaboration agreement | Development event milestones
Collaborations and grants
Collaboration revenue recognized		$10	$7.50
Collaboration agreement | Roche and SMA Foundation
Collaborations and grants
Deferred revenue				30
Collaboration revenue recognized	20.2				26.6	18.4
Number of compounds in preclinical development				3
Number of significant deliverables				2
Research period for applying technology				2 years
Collaboration agreement | Roche and SMA Foundation | Development event milestones | Maximum
Collaborations and grants
Additional consideration receivable upon achievement of specified events	135
Collaboration agreement | Roche and SMA Foundation | Sales milestones | Maximum
Collaborations and grants
Additional consideration receivable upon achievement of specified events	325
Early stage collaboration and discovery agreements
Collaborations and grants
Deferred revenue	1.8				0.9
Collaboration revenue recognized	1.3				4.8
Number of significant deliverables							2
Early stage collaboration and discovery agreements | Minimum
Collaborations and grants
Research period for applying technology	3 years
Early stage collaboration and discovery agreements | Maximum
Collaborations and grants
Research period for applying technology	4 years
Early stage collaboration and discovery agreements | Development event milestones
Collaborations and grants
Additional consideration receivable upon achievement of specified events	143
Early stage collaboration and discovery agreements | Sales milestones | Maximum
Collaborations and grants
Additional consideration receivable upon achievement of specified events	252

Income_taxes_Details

Income taxes (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Current:
U.S. State and local	($4,890)	$2
Foreign	197
Current Income Tax Expense (Benefit), Total	-4,693	2
Reconciliation of the U.S. statutory income tax rate to the entity's effective tax rate
Federal income tax (benefit) at statutory rate (as a percent)	34.00%	34.00%	34.00%
State income tax benefit, net of federal benefit (as a percent)	-1.60%	5.65%	3.80%
Permanent differences (as a percent)	-0.93%	-5.90%
NOL IRC Section 382 Limitations	-21.53%
Research and development (as a percent)	3.78%	15.88%
Increase to valuation allowance (as a percent)	9.17%	-49.63%	-35.80%
Foreign Taxes	-18.14%
Other (as a percent)	0.01%		-2.00%
Effective income tax rate (as a percent)	4.76%	0.00%	0.00%
Deferred tax assets:
Amortization	69	80
Depreciation	2,268	1,922
Accrued expense	611	333
Deferred revenue	699	350
Federal tax credits	17,807	14,082
State tax credits	1,274	1,587
Federal net operating losses	76,933	88,188
State net operating losses	9,185	10,457
Capitalized research and development costs	10,585	12,254
Other	3,852	3,212
Total gross deferred tax assets	123,283	132,465
Less valuation allowance	$123,283	$132,465

Income_taxes_Details_2

Income taxes (Details 2) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Income taxes
Change in valuation allowance	$9.20	$25.60
Federal
Operating loss carryforwards
Net operating loss carryforwards	226.3
State
Operating loss carryforwards
Net operating loss carryforwards	$154.60

Income_taxes_Details_3

Income taxes (Details 3) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014
Credit carryforwards
Orphan drug credit carryover	$11.40
Limited NOL carryforwards	231.5
Operating loss carryforwards, not subject to expiration	169.2
NOL carryforward period	20 years
Operating loss carryforwards, subject to expiration	62.3
Operating loss carryforwards for immediate use	82.1
Operating loss carryforwards in next twelve months	16.7
Federal
Credit carryforwards
Credit carryforwards	6.5
Net operating loss carryforwards	226.3
State
Credit carryforwards
Credit carryforwards	1.7
Net operating loss carryforwards	154.6
First five years from ownership change
Credit carryforwards
Net operating loss carryforwards	16.7
After five years
Credit carryforwards
Net operating loss carryforwards	$5.70

Income_taxes_Details_4

Income taxes (Details 4) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating loss carryforwards
Net tax benefit	$4,693,000
Uncertain tax position	0	0
U.S. federal income tax rate (as a percent)	34.00%	34.00%	34.00%
New Jersey
Operating loss carryforwards
Net tax benefit	4,900,000
State | New Jersey
Operating loss carryforwards
Net operating loss carryforwards sold under the Technology Business Tax Certificate Transfer Program	$50,400,000

Commitments_and_contingencies_1

Commitments and contingencies (Details) (USD $)	12 Months Ended	24 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Commitments and contingencies
Operating Leases, Rent Expense, Net	$900,000	$700,000
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2015	1,268,000
2016	932,000
2017	923,000
2018	1,035,000
2019	176,000
Total future minimum lease payments	4,334,000
Funding agreement | Wellcome Trust | Maximum
Other contingencies
Development and regulatory milestone payments which the entity may be obligated to pay	$68,900,000

Geographic_segments_Details

Geographic segments (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	item
Revenues from External Customers and Long-Lived Assets [Line Items]
Number of Operating Segments	1
Total assets	$333,219	$151,903
Property and equipment, net	9,159	6,730
Revenue, Net	25,245	34,696	33,946
Operating Segments
Revenues from External Customers and Long-Lived Assets [Line Items]
Total assets	333,219	151,903
Property and equipment, net	9,159	6,730
Revenue, Net	25,245	34,696
US
Revenues from External Customers and Long-Lived Assets [Line Items]
Total assets	330,663	151,903
Property and equipment, net	8,555	6,730
Revenue, Net	25,245	34,696
Non US
Revenues from External Customers and Long-Lived Assets [Line Items]
Total assets	2,556
Property and equipment, net	$604

401k_plan_Details

401(k) plan (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
401(k) plan
Matching contribution up to the first 6% of employee's base salary (as a percent)	33.00%
Percentage of employee's base salary, matched by employer	6.00%
Expense recorded	$0.30	$0.10	$0.20

Selected_quarterly_financial_d2

Selected quarterly financial data (Details) (USD $)	1 Months Ended	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Jul. 31, 2012	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Selected quarterly financial data
Net Product Sales		$636	$81							$717
Collaboration and grant revenue		12,022	1,613	1,677	9,217	4,411	16,290	6,854	7,142
Operating Expenses		44,888	29,295	27,046	23,429	22,503	20,565	21,307	15,718	124,658	80,094	60,754
Loss from operations		-32,230	-27,601	-25,369	-14,212	-18,093	-4,276	-14,453	-8,576	-99,413	-45,398	-26,808
Net loss						-17,886	-4,416	-14,587	-14,685	-93,753	-51,574	-26,235
Deemed Dividend									18,249		18,249
Gain on exchange of convertible preferred stock in connection with recapitalization	160,000								3,391		3,391	159,954
Less beneficial conversion charge												-378
Net income (loss) attributable to common stockholders		($27,269)	($27,282)	($25,104)	($14,098)	($17,886)	($4,416)	($14,587)	($29,543)	($93,753)	($66,432)	$133,341
Basic net income (loss) per common share		($0.84)	($0.93)	($0.86)	($0.58)	($0.75)	($0.19)	($5.51)	($6,527.30)	($2.97)	($5.18)	$219.76
Diluted net income (loss) per common share		($0.84)	($0.93)	($0.86)	($0.58)	($0.75)	($0.19)	($5.51)	($6,527.30)	($2.97)	($5.18)	$42.50