PTC Therapeutics (PTCT) 10-K 6 Mar 14 2013 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2013	Mar. 04, 2014	Jun. 28, 2013
Document and Entity Information	'	'	'
Entity Registrant Name	'PTC THERAPEUTICS, INC.	'	'
Entity Central Index Key	'0001070081	'	'
Document Type	'10-K	'	'
Document Period End Date	31-Dec-13	'	'
Amendment Flag	'false	'	'
Current Fiscal Year End Date	'--12-31	'	'
Entity Well-known Seasoned Issuer	'No	'	'
Entity Voluntary Filers	'No	'	'
Entity Current Reporting Status	'Yes	'	'
Entity Filer Category	'Non-accelerated Filer	'	'
Entity Public Float	'	'	$260,280,900
Entity Common Stock, Shares Outstanding	'	30,076,773	'
Document Fiscal Year Focus	'2013	'	'
Document Fiscal Period Focus	'FY	'	'

Balance_sheets

Balance sheets (USD $)	Dec. 31, 2013	Dec. 31, 2012
Current assets:	'	'
Cash and cash equivalents	$15,414,403	$2,725,702
Marketable securities	127,053,124	'
Prepaid expenses and other current assets	1,599,200	855,750
Grant and collaboration receivables, net	957,722	1,013,813
Total current assets	145,024,449	4,595,265
Fixed assets, net	6,729,364	8,280,037
Deposits and other assets	149,008	197,050
Total assets	151,902,821	13,072,352
Current liabilities:	'	'
Accounts payable and accrued expenses	12,207,383	7,023,971
Current portion of long-term debt	48,622	4,444,171
Deferred revenue	877,434	16,690,747
Total current liabilities	13,133,439	28,158,889
Deferred revenue, less current portion	'	741,667
Long-term debt, less current portion	'	438,810
Other long-term liabilities	2,226,970	2,549,719
Total liabilities	15,360,409	31,889,085
Commitments and contingencies (Note 13)	'	'
Stockholders' equity (deficit):	'	'
Preferred stock, $0.001 par value. Undesignated 5,000,000 shares; issued and outstanding 0 shares at December 31, 2013	'	'
Common stock, $0.001 par value. Authorized 125,000,000 shares; issued and outstanding 23,803,282 shares at December 31, 2013 Authorized 17,000,000 shares; issued and outstanding 4,526 shares at December 31, 2012	24,344	545
Additional paid-in capital	465,245,968	177,583,672
Accumulated other comprehensive income	70,393	'
Accumulated deficit	-328,798,293	-277,224,718
Total stockholders' equity (deficit)	136,542,412	-99,640,501
Total liabilities, convertible preferred stocks and stockholders' equity (deficit)	151,902,821	13,072,352
Series One convertible preferred stock	'	'
Current liabilities:	'	'
Preferred stock	'	62,263,852
Series Two convertible preferred stock	'	'
Current liabilities:	'	'
Preferred stock	'	18,182,129
Series Three convertible preferred stock	'	'
Current liabilities:	'	'
Preferred stock	'	$377,787

Balance_sheets_Parenthetical

Balance sheets (Parenthetical) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Common stock, par value (in dollars per share)	$0.00	$0.00
Common stock, authorized shares	125,000,000	17,000,000
Common stock, issued shares	23,803,282	4,526
Common stock, outstanding shares	23,803,282	4,526
Series One convertible preferred stock	'	'
Preferred stock, designated shares	'	2,000,000
Preferred stock, issued shares	'	1,483,337
Preferred stock, outstanding shares	'	1,483,337
Series Two convertible preferred stock	'	'
Preferred stock, designated shares	'	13,750,000
Preferred stock, issued shares	'	10,701,405
Preferred stock, outstanding shares	'	10,701,405
Series Three convertible preferred stock	'	'
Preferred stock, designated shares	'	13,750,000
Preferred stock, issued shares	'	2,853,517
Preferred stock, outstanding shares	'	2,853,517
Preferred stock	'	'
Preferred stock, par value (in dollars per share)	$0.00	'
Preferred stock, undesignated shares	5,000,000	'
Preferred stock, issued shares	0	'
Preferred stock, outstanding shares	0	'

Statements_of_operations

Statements of operations (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues:	'	'	'
Collaboration revenue	$31,326,117	$28,779,078	$98,960,851
Grant revenue	3,370,210	5,166,985	6,451,296
Total revenues	34,696,327	33,946,063	105,412,147
Operating expenses:	'	'	'
Research and development	54,875,144	46,138,868	58,677,081
General and administrative	25,218,652	14,615,376	16,153,069
Total operating expenses	80,093,796	60,754,244	74,830,150
(Loss) income from operations	-45,397,469	-26,808,181	30,581,997
Interest expense, net	-6,083,655	-1,209,577	-2,444,417
Loss on extinguishment of debt	-129,963	'	'
Other income, net	37,512	1,782,656	461,358
(Loss) income from operations before tax benefit	-51,573,575	-26,235,102	28,598,938
Tax benefit	'	'	2,305,576
Net (loss) income	-51,573,575	-26,235,102	30,904,514
Deemed dividend	-18,248,768	'	'
Gain on exchange of convertible preferred stock in connection with recapitalization	3,390,750	159,954,069	'
Less beneficial conversion charge	'	-377,787	'
Net (loss) income attributable to common stockholders	($66,431,593)	$133,341,180	$30,904,514
Net (loss) income attributable to common stockholders per share:	'	'	'
Basic (in dollars per share)	($5.18)	$219.76	$23.95
Diluted (in dollars per share)	($5.18)	$42.50	$4.55
Weighted-average shares outstanding:	'	'	'
Basic (in shares)	12,829,411	3,328	1,089
Diluted (in shares)	12,829,411	17,205	5,729

Statements_of_comprehensive_lo

Statements of comprehensive (loss) income (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statements of comprehensive (loss) income	'	'	'
Net (loss) income	($51,573,575)	($26,235,102)	$30,904,514
Other comprehensive (loss) income:	'	'	'
Unrealized (loss) gain on marketable securities	70,393	'	-3,606
Comprehensive (loss) income	($51,503,182)	($26,235,102)	$30,900,908

Statements_of_convertible_pref

Statements of convertible preferred stock and changes in stockholders' equity (deficit) (USD $)	Total	Common stock	Additional paid-in capital	Accumulated other comprehensive income (loss)	Accumulated deficit	Series A-G convertible preferred stock	Series One-Three convertible preferred stock	Series Four convertible preferred stock	Series Five convertible preferred stock
Balance at Dec. 31, 2010	($272,328,123)	$131	$9,184,483	$3,606	($281,516,343)	'	'	'	'
Balance, beginning of period at Dec. 31, 2010	'	'	'	'	'	214,379,914	'	'	'
Balance (in shares) at Dec. 31, 2010	'	130,586	'	'	'	'	'	'	'
Balance, beginning of period (in shares) at Dec. 31, 2010	'	'	'	'	'	154,728,267	'	'	'
Increase (Decrease) in Stockholders' Equity	'	'	'	'	'	'	'	'	'
Exercise of stock options	5,889	2	5,887	'	'	'	'	'	'
Exercise of stock options (in shares)	'	1,536	'	'	'	'	'	'	'
Share-based compensation expense	2,816,637	'	2,816,637	'	'	'	'	'	'
Net (loss) income	30,904,514	'	'	'	30,904,514	'	'	'	'
Unrealized gain (loss) on investments	-3,606	'	'	-3,606	'	'	'	'	'
Balance at Dec. 31, 2011	-238,604,689	133	12,007,007	'	-250,611,829	'	'	'	'
Balance (in shares) at Dec. 31, 2011	'	132,122	'	'	'	'	'	'	'
Balance, beginning of period at Dec. 31, 2011	'	'	'	'	'	214,379,914	'	'	'
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	2,956,829	412	2,956,417	'	'	'	'	'	'
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) income	-26,235,102	'	'	'	-26,235,102	'	'	'	'
Balance at Dec. 31, 2012	-99,640,501	545	177,583,672	'	-277,224,718	'	'	'	'
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	131,649,688	9,628	131,640,060	'	'	'	'	'	'
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	162,467,146	14,171	162,452,975	'	'	'	'	'	'
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) income	-51,573,575	'	'	'	-51,573,575	'	'	'	'
Unrealized gain (loss) on investments	70,393	'	'	70,393	'	'	'	'	'
Balance at Dec. 31, 2013	$136,542,412	$24,344	$465,245,968	$70,393	($328,798,293)	'	'	'	'
Balance (in shares) at Dec. 31, 2013	'	23,803,282	'	'	'	'	'	'	'

Statements_of_cash_flows

Statements of cash flows (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash flows from operating activities	'	'	'
Net (loss) income	($51,573,575)	($26,235,102)	$30,904,514
Adjustments to reconcile net (loss) income to net cash used in operating activities:	'	'	'
Depreciation	2,396,405	2,704,151	2,871,200
Change in valuation of warrant liability	-37,507	-1,782,655	-461,947
Noncash interest expense	6,048,580	225,730	416,612
Loss on extinguishment of debt	129,963	'	'
Share-based compensation expense	8,427,188	2,288,392	2,816,637
Changes in operating assets and liabilities:	'	'	'
Prepaid expenses and other current assets	-760,501	2,452,430	-1,355,123
Grant and collaboration receivables	56,091	230,315	2,052,550
Deposits and other assets	48,042	83,817	214,345
Accounts payable and accrued expenses	5,183,412	-6,025,483	-3,159,711
Other long-term liabilities	-285,242	102,757	-67,151
Deferred revenue	-16,554,980	-21,972,143	-54,998,713
Net cash used in operating activities	-46,922,124	-47,927,791	-20,766,787
Cash flows from investing activities	'	'	'
Purchases of fixed assets	-845,732	-188,681	-165,116
Purchases of marketable securities	-156,044,515	'	-2,019,163
Maturities of marketable securities	29,061,784	'	29,887,327
Net cash (used in) provided by investing activities	-127,828,463	-188,681	27,703,048
Cash flows from financing activities	'	'	'
Payments on long-term debt	-4,995,763	-6,943,988	-7,185,610
Net proceeds from sale of Series One preferred stock	'	29,354,752	'
Net proceeds from sale of Series Four preferred stock	60,785,363	'	'
Net proceeds from IPO	131,649,688	'	'
Proceeds from issuance of common stock	'	'	5,889
Net cash provided by (used in) financing activities	187,439,288	22,410,764	-7,179,721
Net increase (decrease) in cash and cash equivalents	12,688,701	-25,705,708	-243,460
Cash and cash equivalents, beginning of period	2,725,702	28,431,410	28,674,870
Cash and cash equivalents, end of period	15,414,403	2,725,702	28,431,410
Supplemental disclosure of cash information	'	'	'
Cash paid for interest	367,065	1,211,764	2,486,682
Cash paid for income taxes	2,077	2,000	2,077
Supplemental disclosures of noncash information related to investing and financing activities	'	'	'
Change in unrealized gain (loss) on marketable securities	70,393	'	-3,606
Change in carry value of preferred securities resulting from recapitalization	$3,390,750	$159,954,069	'

The_Company

The Company	12 Months Ended
	Dec. 31, 2013
The Company	'
The Company	'
	1. The Company
	PTC Therapeutics, Inc. (the Company or PTC) was incorporated as a Delaware corporation on March 31, 1998. The Company is a biopharmaceutical company focused on the discovery and development of orally administered, proprietary small-molecule drugs that target post-transcriptional control processes.
	The Company has devoted substantially all of its efforts to research and development, including clinical trials. The Company has not completed development of any drugs. The Company has not generated 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, 2013, the Company had an accumulated deficit of approximately $328.8 million. The Company has financed its operations to date primarily through a public offering in February 2014, its initial public offering 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. The Company believes that its existing cash, cash equivalents, and marketable securities provide for sufficient resources to fund its currently planned operations through 2016.

Summary_of_significant_account

Summary of significant accounting policies	12 Months Ended
	Dec. 31, 2013
Summary of significant accounting policies	'
Summary of significant accounting policies	'
	2. Summary of significant accounting policies
	Basis of Presentation
	The accompanying 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.
	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 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
	Management determines the classification of marketable securities at the time of purchase and reevaluates such designation as of each balance sheet date. Marketable securities are classified as available-for-sale and carried at fair value, with any unrealized gain or loss recorded as a separate component of stockholders' equity (deficit).
	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
	Grant and collaboration receivables
	The Company records receivables in conjunction with grant and collaboration agreements when the services have been performed. The Company will record an allowance for bad debt if receivables are anticipated to be uncollectible. There is no indication that any receivables are uncollectible as of December 31, 2013 and 2012. Write-offs of receivables have historically been insignificant.
	Concentration of risks
	The Company has no significant off-balance sheet risk or credit risk concentrations. The Company maintains its cash and cash equivalents with various financial institutions. The Company maintains cash accounts that may at times exceed the federally insured limit; however, it has not experienced and does not anticipate experiencing any credit losses from maintaining cash accounts in excess of such limits.
	The Company's revenues from its two largest collaboration partners and its largest grant as a percentage of total revenues were 80%, 10%, and 8%; 67%, 11%, and 9%; 85%, 8%, and 3%, for 2013, 2012, and 2011, respectively.
	Reverse stock split
	As a result of the one-for-120 reverse stock split that was effected on March 7, 2013, each 120 shares of the Company's outstanding common stock were reclassified and combined into one share of common stock. All references to common stock have been restated to reflect the reverse stock split on a retroactive basis.
	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.
	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.
	The Company's revenue is generated primarily through collaborative research and development and licensing agreements and grants.
	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.
	For existing collaborations entered into prior to the adoption in 2011 of the revised multiple element revenue recognition guidance described below, the Company recognized revenue consistent with the approach established at the inception of each arrangement. For these existing collaborations, where the Company has continuing involvement, the Company recorded nonrefundable, upfront fees as deferred revenue and recognizes revenue on a straight-line basis as collaboration revenue over the expected performance period.
	For new collaborations or for material modifications made to existing collaborations, in 2011 and thereafter, the Company adopted the updated multiple element revenue recognition guidance. Under this new guidance, all non-contingent arrangement consideration is allocated to the identified units of accounting based on their relative selling price at inception of the collaboration arrangement. The Company derives the selling price using a combination of internal subjective and available external objective information, such as comparable transactions. The Company recognizes revenue commensurate with delivery, such as in the case with delivery of a license, or ratably over the course of a service period, as appropriate, such as in the case of ongoing research and development activities.
	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 Company had deferred research and development advance payments of approximately $0.2 million as of December 31, 2012. The deferred research and development advance payments were 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 grant and collaboration 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 and preferred stock that include a put feature, 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 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, 2013.
	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.
	Prior to becoming a public company, the Company utilized various valuation methodologies in accordance with the framework of the 2004 American Institute of Certified Public Accountants Technical Practice Aid, Valuation of Privately-Held Company Equity Securities Issued as Compensation, to estimate the fair value of its stock. The methodologies included an option pricing method to estimate the Company's underlying equity value, and a methodology that determined an estimated value under an initial public offering (IPO) scenario and a sale scenario based upon an assessment of the probability of occurrence of each scenario. Each valuation methodology included estimates and assumptions that required the Company's judgment. These estimates included assumptions regarding future performance, including the completion of clinical trials and the time to complete an IPO or sale of the Company. As with any valuation, significant changes to the key assumptions used in the valuations could result in different fair values of common stock at each valuation date.
	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 (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.

Fair_value_of_financial_instru

Fair value of financial instruments and investments	12 Months Ended
	Dec. 31, 2013
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, 2013 and 2012:
		December 31, 2013
		Total			Quoted prices in		Significant			Significant
					active markets for		other			unobservable
					identical assets		observable			inputs
					(level 1)		inputs			(level 3)
							(level 2)
	Marketable securities	$	127,053,124		$	—	$	127,053,124		$	—
	Warrant liability	$	58,154		$	—	$	—		$	58,154
		December 31, 2012
		Total			Quoted prices in		Significant			Significant
					active markets for		other			unobservable
					identical assets		observable			inputs
					(level 1)		inputs			(level 3)
							(level 2)
	Warrant liability	$	95,661		$	—	$	—		$	95,661
	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, 2013.
	The following is a summary of marketable securities accounted for as available-for-sale securities at December 31, 2013:
		December 31, 2013
					Gross Unrealized
		Amortized								Fair
		Cost			Gains		Losses			Value
	Commercial paper	$	14,993,309		$	5,151	$	—		$	14,998,460
	U.S. corporate debt securities		111,989,422			96,737		(31,495	)		112,054,664
		$	126,982,731		$	101,888	$	(31,495	)	$	127,053,124
	Unrealized gains and losses are reported as a component of accumulated other comprehensive (loss) income in stockholders' equity (deficit). During the year ended December 31, 2013, the proceeds from the sale of marketable securities and realized gains/losses were immaterial. 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, 2013, 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, 2013 mature as follows:
		December 31, 2013
		Less Than			More Than
		12 Months			12 Months
	Commercial paper	$	14,998,460		$	—
	U.S. corporate debt securities		54,158,359			57,896,305
	Total Marketable securities	$	69,156,819		$	57,896,305
	There were no marketable securities as of December 31, 2012.
	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 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, 2013 and 2012:
		Level 3 assets
	Beginning balance January 1, 2012	$	1,878,316
	Change in fair value of warrant liability		(1,782,655	)
	Ending balance as of December 31, 2012	$	95,661
	Change in fair value of warrant liability		(37,507	)
	Ending balance as of December 31, 2013	$	58,154
	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, 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). The significant assumptions used in preparing the option pricing model for valuing the Company's warrants as of December 31, 2012 include (i) volatility (87%), (ii) risk free interest rate (0.16%-1.18%), (iii) strike price ($16.00), (iv) fair value of preferred shares ($2.35) and (v) expected life (1.0-7.0 years). The fair value of the preferred shares declined significantly due to the recapitalization of the Company's outstanding convertible preferred stock in June 2012 as described in Note 7.

Fixed_assets

Fixed assets	12 Months Ended
	Dec. 31, 2013
Fixed assets	'
Fixed assets	'
	4. Fixed assets
	Fixed assets, net were as follows at December 31, 2013 and 2012:
		December 31,
		2013			2012
	Leasehold improvements	$	12,473,836		$	12,473,836
	Computer equipment and software		2,284,836			2,118,713
	Furniture, fixtures, and lab equipment		14,283,875			13,969,758
	Assets not yet placed in service		369,644			4,152
			29,412,191			28,566,459
	Less accumulated depreciation and amortization		(22,682,827	)		(20,286,422	)
		$	6,729,364		$	8,280,037
	Depreciation expense was approximately $2.4 million, $2.7 million, and $2.9 million for the years ended December 31, 2013, 2012 and 2011, respectively.

Accounts_payable_and_accrued_e

Accounts payable and accrued expenses	12 Months Ended
	Dec. 31, 2013
Accounts payable and accrued expenses	'
Accounts payable and accrued expenses	'
	5. Accounts payable and accrued expenses
	Accounts payable and accrued expenses at December 31, 2013 and 2012 consist of the following:
		December 31,
		2013		2012
	Employee compensation, benefits, and related accruals	$	5,102,795	$	3,096,475
	Consulting and contracted research		4,006,336		2,515,678
	Professional fees		1,294,637		559,228
	Accounts payable		1,123,895		621,591
	Other		679,720		230,999
		$	12,207,383	$	7,023,971

Longterm_debt

Long-term debt	12 Months Ended
	Dec. 31, 2013
Long-term debt.	'
Long-term debt	'
	6. Long-term debt
	In May 2009, the Company entered into a capital lease for a laboratory instrument. This lease carries an implied interest rate of 8.2% and is payable in fixed monthly installments. As of December 31, 2013 and 2012, the Company had approximately $0.1 million and $0.2 million of remaining principal, respectively, which approximates the fair value.
	In September 2009, the Company entered into a $25.0 million secured debt facility with a syndicate of two lenders. In conjunction with entering into the debt facility, the Company issued warrants to purchase 62,500 shares of Series F-2 convertible preferred stock at an exercise price of $16.00 per share to the lenders. The warrants became exercisable in proportion to the amount of the facility borrowed. The fair value of the warrants was reflected as a discount to debt, and this discount is accreted to interest expense over the term of the debt facility.
	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 are secured by substantially all of the Company's assets except for intellectual property. The notes carry a fixed interest rate of 13.65% and required interest-only payments for the first five months, with principal repayment beginning in month six and continuing for 30 months. As of December 31, 2011 warrants to acquire 56,250 shares of Series F-2 were exercisable. In connection with the recapitalization of the Company's outstanding convertible preferred stock in 2012, these warrants were amended to be warrants to purchase Series Two convertible preferred stock. As of December 31, 2012, the outstanding balance on the notes was $4.8 million.
	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, 2013
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 be 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 $0.8 million, $0.4 million, $15.0 million, $42.6 million, $50.0 million, $26.6 million, $10.0 million, $24.2 million, and $50.3 million 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 has not declared 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 represents 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 are as follows:
	Dividends—The holders of Series One and Series Two, in preference to the holders of common stock, are entitled to noncumulative dividends when and if declared by the Board of Directors. The holders of Series Three are not entitled to dividends. The Company has not declared any dividends through December 31, 2012.
	Liquidation—Upon the liquidation, dissolution, reorganization or winding-up of the Company, the holders of Series One will be entitled to receive, before any distribution or payment is 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 are excess assets to distribute, the holders of Series Two will be entitled to receive 76.47% of such excess assets, and the holders of Series One will be entitled to receive 23.53% of such excess assets, until the holders of Series Two receive 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 are remaining assets after Series Two distributions, the holders of Series Three are entitled to receive 8.82% of such remaining assets, and the holders of Series One and Series Two will be entitled to receive 23.53% and 67.65%, respectively, of such remaining assets, until the holders of Series Three receive 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 are remaining assets to distribute, the holders of Series One, Series Two, and Series Three will be entitled to receive 20%, 55%, and 25% of such remaining assets, respectively.
	Voting—Each holder of Series One is 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 convert. Except as required by law, holders of Series Two and Series Three have limited voting rights. Additionally, the holders of Series One, voting as a single class, are entitled to elect twelve members of the Board of Directors.
	Conversion—Each share of Series One is convertible at any time at the option of the holder into two shares of common stock. Each share of Series Two and Series Three is convertible at any time at the option of the holder into one share of common stock. These conversion ratios are 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 $6.0 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 $54.0 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, are 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 will be entitled to receive, before any distribution or payment is 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 are excess assets to distribute, the holders of Series Five will be entitled to receive, before any distribution or payment is 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 are remaining assets to distribute, the holders of common stock will be entitled to receive such remaining assets.
	Voting—Each holder of Series Four and Series Five are entitled to cast the number of votes into which such holder's shares would convert. Except as required by law, holders of common stock have limited voting rights. Additionally, except as required by law, and except in certain enumerated circumstances, holders of Series Four and Series Five shall vote 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 are 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.
	Warrants
	All of the Company's outstanding warrants are classified as liabilities as of December 31, 2013 and 2012 because they contain either non-standard antidilution provisions or they were exercisable into preferred shares that include a put feature.
	The following is a summary of the Company's outstanding warrants as of December 31, 2013:
		Warrant shares		Exercise price		Expiration
	Common stock		1,428	$	128		2014
	Common stock		6,250	$	128		2017
	Common stock		7,030	$	128		2019 and 2020
	Common stock		452	$	2,520.00		2014
	The following is a summary of the Company's outstanding warrants as of December 31, 2012:
		Warrant shares		Exercise price		Expiration
	Series Two		24,712	$	16		2014
	Series Two		50,000	$	16		2017
	Series Two		56,250	$	16		2019 and 2020
	Common stock		645	$	2,520		2013 and 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, 2013
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 2011 and 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 and $30.9 million for the years ended 2012 and 2011, respectively, for net income attributable to participating securities.
	The diluted earnings per share for the years ended December 31, 2012 and 2011 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
		2013			2012			2011
	Numerator
	Net (loss) income	$	(51,573,575	)	$	(26,235,102	)	$	30,904,514
	Deemed dividend		(18,248,768	)		—			—
	Gain on exchange of convertible preferred stock in connection with recapitalization		3,390,750			159,954,069			—
	Less beneficial conversion charge		—			(377,787	)		—
	Less net income attributable to participating preferred stock		—			(132,609,918	)		(30,878,445	)
	Net (loss) income attributable to common stockholders	$	(66,431,593	)	$	731,262		$	26,069
	Denominator
	Denominator for basic earnings per share		12,829,411			3,328			1,089
	Effect of dilutive securities:
	Employee stock options		—			—			4,640
	Series 3 convertible preferred stock		—			13,877			—
	Denominator for diluted earnings per share		12,829,411			17,205			5,729
	Net (loss) income per share:
	Basic		(5.18	)		219.76			23.95
	Diluted		(5.18	)		42.5			4.55

Stock_option_plan

Stock option plan	12 Months Ended
	Dec. 31, 2013
Stock option plan	'
Stock option plan	'
	9. Stock option 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 Stock Incentive Plan, which provides for the granting of stock option awards, restricted stock awards, and other stock-based and cash-based awards.
	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) 122,296 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 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, 2013, awards for 96,917 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.
	A summary of stock option activity is as follows:
		Number of			Exercise price			Weighted-			Weighted-		Aggregate
		options						average			average		intrinsic
								exercise			remaining		value
								price			contractual
											term
	Outstanding at December 31, 2010		39,557		$	226.80 - $1,149.60		$	547.2
	Granted		8,123		$	490.8		$	490.8
	Exercised		(11	)	$	451.20 - $508.80		$	459.6
	Forfeited		(875	)	$	226.80 - $1,149.60		$	757.2
	Outstanding at December 31, 2011		46,794		$	226.80 - $1,149.60		$	532.8			5.74 years
	Granted		5,715		$	218.4		$	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	$	11,905,903
	Vested or expected to vest at December 31, 2013		1,971,286					$	20.78			9.28 years	$	11,209,761
	Exercisable at December 31, 2013		146,340					$	129.81			7.90 years	$	688,971
	The total intrinsic value (the excess of the market price over the exercise price) for stock options exercised in 2011 was immaterial. There were no stock option exercises in 2013 or 2012.
	The fair value of grants made in the years ended December 31, 2013, 2012 and 2011 was contemporaneously estimated on the date of grant using the following assumptions:
		2013			2012			2011
	Risk-free interest rate		0.85 - 1.90	%		1.14	%		2.4	%
	Expected volatility		87 - 89	%		87	%		87	%
	Expected term		6.00 - 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, 2013, 2012 and 2011 was $8.23, $160.65 and $364.80, 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, 2013:
		Outstanding
											Exercisable
								Weighted-Average
								Remaining
								Contractual
	Range of Exercise Price	Number of			Weighted-Average			Life (in years)			Number of		Weighted Average
		Options			Exercise						Options		Exercise Price
					Price
	$10.59 - $10.85		1,945,213		$	10.85			9.37			109,113	$	10.84
	$10.85 - $20.76		109,400		$	19.43			9.87			—	$	—
	$20.76 - $490.80		28,226		$	311.28			3.75			24,676	$	309.97
	$490.80 - 735.60		8,964		$	673.95			3.87			8,966	$	673.95
	$1,149.60		3,789		$	1,149.60			6.01			3,585	$	1,149.60
			2,095,592									146,340
	In December 2013, the Compensation Committee of the Board of Directors modified the terms of certain performance based 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.
	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 of			Weighted
		Shares			Average Grant
					Date Fair
					Value
	January 1, 2013		—			—
	Granted		1,131,524		$	10.68
	Vested		—		$	—
	Forfeited		(21,298	)	$	10.65
	Unvested at December 31, 2013		1,110,226		$	10.68
The Company recorded share-based compensation expense in the statement of operations as follows:
	Year ended December 31,
	2013			2012			2011
Research and development	$	2,039,880		$	804,576		$	916,495
General and administrative		6,387,308			1,483,816			1,900,142
Total	$	8,427,188		$	2,288,392		$	2,816,637
The Company utilizes newly issued shares to satisfy stock option exercises.
As of December 31, 2013, there was approximately $21.6 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 2.49 years.

Other_comprehensive_income_los

Other comprehensive income (loss) and accumulated other comprehensive items	12 Months Ended
	Dec. 31, 2013
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, 2013, 2012, and 2011, respectively.
		Unrealized			Total Accumulated
		Gains On			Other
		Marketable			Comprehensive
		Securities			Items
	Balance at January 1, 2011	$	3,606		$	3,606
	Other comprehensive loss before reclassifications		(3,606	)		(3,606	)
	Amounts reclassified from other comprehensive items		—			—
	Other comprehensive income/(loss)		—			—
	Balance at December 31, 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		70,393			70,393
	Amounts reclassified from other comprehensive items		—			—
	Other comprehensive income		70,393			70,393
	Balance at December 31, 2013	$	70,393		$	70,393

Collaborations_and_grants

Collaborations and grants	12 Months Ended
	Dec. 31, 2013
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. During 2011, the Genzyme collaboration was modified and later terminated. The following are the key terms to the Company's (i) terminated collaboration with Genzyme, (ii) ongoing collaborations and (iii) early stage discovery and development arrangements.
	Terminated collaboration
	Genzyme
	In July 2008, Genzyme Corporation (now a Sanofi company) and the Company entered into an exclusive global collaboration to develop and commercialize ataluren, the Company's novel oral therapy in late-stage development for the treatment of genetic disorders due to nonsense mutations. Under the terms of this agreement, the Company granted Genzyme rights to commercialize ataluren in all countries except the United States and Canada, which rights the Company retained. Genzyme made a nonrefundable upfront payment to the Company of $100.0 million in July 2008, which was being recognized over the Company's estimated period of performance under the arrangement.
	In August 2011, the Company and Genzyme announced a restructuring of the agreement. Under the terms of the restructuring, the Company regained worldwide rights to ataluren and Genzyme made an additional payment of $7.5 million to the Company in exchange for an option to commercialize ataluren in indications other than nonsense mutation Duchenne muscular dystrophy (nmDMD) outside the United States and Canada. On March 27, 2012, the Company received notification that Genzyme declined to exercise the option, at which time the option expired. As a result, the collaboration was terminated.
	The Company evaluated the August 2011 restructuring of the Genzyme collaboration agreement and determined it to be a material modification to the original agreement for financial reporting purposes pursuant to the revised multiple element revenue recognition guidance. The Company determined that given the significance of the changes in relation to the initial arrangement, including the decrease in the total consideration that could be paid to the Company, the significant removal of existing deliverables, the significant changes in the intellectual property rights and the significant change in the performance period, the initial arrangement had been effectively terminated. The Company elected to reevaluate the amended agreement and performed an analysis to calculate the estimated selling price of the undelivered elements of the arrangement. Based on this analysis, the Company determined that the undelivered element had an estimated selling price of $8.8 million, and as such, adjusted the Company's deferred revenue balance to reflect this amount as of the contract amendment date. The Company amortized the balance through the option period. The effect of this reevaluation was to recognize approximately $79.0 million as of the restructuring date. For the years ended December 31, 2011 and 2012, the Company recognized approximately $90.0 million and $3.8 million respectively, in collaboration revenue from Genzyme.
	Current collaboration
	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 and Roche agreed to provide funding for research activities performed on its behalf.
	The Company applied the revised 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 is being recognized over the estimated performance period of two years, which is the contracted research period. For the year ended December 31, 2013 and 2012, the Company recognized approximately $26.6 million and $18.4 million respectively, in collaboration revenue. The balance of the remaining deferred upfront payment was $0 at 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 $135.0 million in research and development event milestones, up to $325.0 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.
	Early stage collaboration and discovery agreements
	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.
	For those arrangements entered into or significantly modified after January 1, 2011, the Company applies the revised 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. However, since the Company's discovery technologies are highly specialized, the Company has determined that the license does not have standalone value without the ongoing research and development services and accounts for these arrangements as a single unit of accounting.
	As a result, the Company has deferred revenue of $0.9 million and $3.0 million as of December 31, 2013 and 2012, respectively, related to these arrangements. For the years ended December 31, 2013 and 2012, the Company recognized approximately $4.8 million and $6.6 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 $143.0 million and up to $252.0 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, 2013
Income taxes	'
Income taxes	'
	12. Income taxes
	A reconciliation of the U.S. statutory income tax rate to the Company's effective tax rate is as follows:
					December 31,
		2013			2012			2011
	Federal income tax (benefit) at statutory rate		34	%		34	%		34	%
	State income tax benefit, net of federal benefit		5.65			3.8			4.2
	Permanent differences		(5.90	)		—			—
	Research and development		15.88			—			—
	Increase to valuation allowance		(49.63	)		(35.80	)		(45.90	)
	Other		—			(2.00	)		(1.60	)
	Effective income tax rate		0	%		0	%		(9.30	)%
	The Company recognized a tax benefit of $2.3 million in connection with the sale of net operating losses and research and development credits in the New Jersey Transfer Program for the year ended December 31, 2011. The significant components of the Company's deferred tax assets and liabilities at December 31, 2013 and 2012 are as follows:
		2013			2012
	Deferred tax assets:
	Amortization	$	80,387		$	91,871
	Depreciation		1,922,332			1,535,952
	Accrued expense		332,539			1,208,846
	Deferred revenue		350,447			6,962,506
	Federal tax credits		14,081,615			5,383,092
	State tax credits		1,587,217			1,094,833
	Federal net operating losses		88,187,475			71,752,278
	State net operating losses		10,456,688			7,619,606
	Capitalized research and development costs		12,254,381			10,479,055
	Other		3,211,720			742,341
	Total gross deferred tax assets		132,464,801			106,870,380
	Less valuation allowance		(132,464,801	)		(106,870,380	)
	Net deferred tax assets	$	—		$	—
	At December 31, 2013 and 2012, the Company recorded a full valuation allowance against its net deferred tax assets of approximately $132.5 million and $106.9 million, respectively. The change in the valuation allowance during the years ended December 31, 2013 and 2012 was approximately $25.6 million and $9.4 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, 2013, the Company has approximately $259.4 million and $176.0 million of federal and state net operating loss carryforwards, respectively. As of December 31, 2013, credit carryforwards for federal and state purposes are approximately $6.0 million and $2.3 million, respectively. 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 2029, and the state credit carryforwards begin to expire in 2022. 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 had a number of equity transactions since inception, and several of these have created ownership changes that could create such a limitation. The Company has not recently performed an analysis to determine the Company's ability to utilize such carryforwards prior to expiration. An analysis will be performed in the future, as necessary.
	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 totaling $28.5 million during 2011. The New Jersey net operating losses sold during 2011 were generated during 2009. For 2011, the Company established a receivable for the $2.3 million, which was received in 2012. The Company did not participate in this program in 2012 or 2013.
	The income tax benefit for the years ended December 31, 2013 and 2012 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 non-deductible expenses, tax credits generated, utilization of net operating loss carryforwards and increases in the Company's valuation allowance. At December 31, 2013 the Company had no unrecognized income tax benefits. The Company applies the accounting guidance for uncertain income tax provisions. This guidance clarifies the accounting for uncertainty in income taxes recognized in financial statements and requires the 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, 2013, the Company did not have any unrecognized tax benefits and has not accrued any interest or penalties through 2013. 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 2010 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.
	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 similar 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 with 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, 2013
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 $0.7 million for each of the years ended December 31, 2013, 2012 and 2011. The Company also leases certain office equipment under operating leases. Future minimum lease payments as of December 31, 2013 are as follows:
	2014	$	890,000
	2015		849,000
	2016		849,000
	2017		849,000
	2018		952,000
	Thereafter		162,000
		$	4,551,000
	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.

401k_plan

401(k) plan	12 Months Ended
	Dec. 31, 2013
401(k) plan	'
401(k) plan	'
	14. 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 20% matching contribution for up to the first 5% of each contributing employee's base salary contributions. The Company made matching contributions to the 401(k) plan and recorded expense of approximately $0.1 million, $0.2 million and $0.2 million for the years ended December 31, 2013, 2012 and 2011, respectively.

Selected_quarterly_financial_d

Selected quarterly financial data	12 Months Ended
	Dec. 31, 2013
Selected quarterly financial data	'
Selected quarterly financial data	'
	15. Selected quarterly financial data
	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 2013 and 2012 are as follows:
		For the quarters ending
		March 31			June 30			September 30			December 31
	2013:00:00
	Collaboration and grant revenue	$	7,141,664		$	6,854,212		$	16,289,573		$	4,410,878
	Operating expenses		15,718,073			21,307,148			20,565,188			22,503,387
	Loss from operations		(8,576,409	)		(14,452,936	)		(4,275,615	)		(18,092,509	)
	Net loss		(14,684,535	)		(14,586,578	)		(4,416,499	)		(17,885,963	)
	Deemed dividend		(18,248,768	)		—			—			—
	Gain on exchange of convertible preferred stock in connection with recapitalization		3,390,750			—			—			—
	Net loss attributable to common stockholders		(29,542,553	)		(14,586,578	)		(4,416,499	)		(17,885,963	)
	Basic net loss per common share(1)	$	(6,527.30	)	$	(5.51	)	$	(0.19	)	$	(0.75	)
	Diluted net loss per common share(1)	$	(6,527.30	)	$	(5.51	)	$	(0.19	)	$	(0.75	)
	2012:00:00
	Collaboration and grant revenue	$	12,525,720		$	7,585,177		$	7,195,076		$	6,640,090
	Operating expenses		18,745,957			15,083,384			14,250,383			12,674,520
	Loss from operations		(6,220,237	)		(7,498,207	)		(7,055,307	)		(6,034,430	)
	Net loss		(6,597,861	)		(6,068,072	)		(7,297,125	)		(6,272,044	)
	Gain on exchange of convertible preferred stock in connection with recapitalization		—			159,954,069			—			—
	Less beneficial conversion charge		—			(377,787	)		—			—
	Net income (loss) attributable to common stockholders		(6,597,861	)		153,508,210			(7,297,125	)		(6,272,044	)
	Basic net income (loss) per common share(1)	$	(5,992.61	)	$	168		$	(1,605.53	)	$	(1,380.13	)
	Diluted net income (loss) per common share(1)	$	(5,992.61	)	$	48.29		$	(1,605.53	)	$	(1,380.13	)
	-1
	The amounts were computed independently for each quarter and the sum of the quarters may not total the annual amounts.

Subsequent_events

Subsequent events	12 Months Ended
	Dec. 31, 2013
Subsequent events	'
Subsequent events	'
	16. Subsequent events
	The Company continues to advance the development of its spinal muscular atrophy (SMA) collaboration with Roche and the SMA Foundation. The collaboration was initially funded in part by the SMA Foundation. In December 2011, the Company announced a partnership with Roche in the collaboration which provided an upfront payment of $30.0 million, up to $460.0 million in milestone payments and royalties on future sales. In August 2013, a development candidate for the program was announced which triggered a $10.0 million milestone payment from Roche. In January 2014, a Phase 1 clinical program was initiated which triggered a $7.5 million milestone payment from Roche. Roche is responsible for pursuing clinical development of compounds from the program consistent with a governance structure that includes representation from the Company and the SMA Foundation and then commercialization of these compounds.
	In February 2014, the Company initiated an underwritten public offering of 4,489,796 million shares of common stock at a public offering price of $24.50 per share, before underwriting discounts. All of the shares in the offering were offered and sold by PTC. In addition, PTC granted the underwriters an option for a period of 30 days to purchase up to 673,469 additional shares of common stock at the public offering price, less the underwriting discount, which the underwriters exercised in full. J.P. Morgan and Credit Suisse acted as joint lead book-running managers for the offering. A registration statement relating to these securities was declared effective by the Securities and Exchange Commission on February 12, 2014. The Company received net proceeds of approximately $118.4 million upon the close of the offering.

Summary_of_significant_account1

Summary of significant accounting policies (Policies)	12 Months Ended
	Dec. 31, 2013
Summary of significant accounting policies	'
Basis of Presentation	'
	Basis of Presentation
	The accompanying 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.
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 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
	Management determines the classification of marketable securities at the time of purchase and reevaluates such designation as of each balance sheet date. Marketable securities are classified as available-for-sale and carried at fair value, with any unrealized gain or loss recorded as a separate component of stockholders' equity (deficit).
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
Grant and collaboration receivables	'
	Grant and collaboration receivables
	The Company records receivables in conjunction with grant and collaboration agreements when the services have been performed. The Company will record an allowance for bad debt if receivables are anticipated to be uncollectible. There is no indication that any receivables are uncollectible as of December 31, 2013 and 2012. Write-offs of receivables have historically been insignificant.
Concentration of risks	'
	Concentration of risks
	The Company has no significant off-balance sheet risk or credit risk concentrations. The Company maintains its cash and cash equivalents with various financial institutions. The Company maintains cash accounts that may at times exceed the federally insured limit; however, it has not experienced and does not anticipate experiencing any credit losses from maintaining cash accounts in excess of such limits.
	The Company's revenues from its two largest collaboration partners and its largest grant as a percentage of total revenues were 80%, 10%, and 8%; 67%, 11%, and 9%; 85%, 8%, and 3%, for 2013, 2012, and 2011, respectively.
Reverse stock split	'
	Reverse stock split
	As a result of the one-for-120 reverse stock split that was effected on March 7, 2013, each 120 shares of the Company's outstanding common stock were reclassified and combined into one share of common stock. All references to common stock have been restated to reflect the reverse stock split on a retroactive basis.
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.
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.
	The Company's revenue is generated primarily through collaborative research and development and licensing agreements and grants.
	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.
	For existing collaborations entered into prior to the adoption in 2011 of the revised multiple element revenue recognition guidance described below, the Company recognized revenue consistent with the approach established at the inception of each arrangement. For these existing collaborations, where the Company has continuing involvement, the Company recorded nonrefundable, upfront fees as deferred revenue and recognizes revenue on a straight-line basis as collaboration revenue over the expected performance period.
	For new collaborations or for material modifications made to existing collaborations, in 2011 and thereafter, the Company adopted the updated multiple element revenue recognition guidance. Under this new guidance, all non-contingent arrangement consideration is allocated to the identified units of accounting based on their relative selling price at inception of the collaboration arrangement. The Company derives the selling price using a combination of internal subjective and available external objective information, such as comparable transactions. The Company recognizes revenue commensurate with delivery, such as in the case with delivery of a license, or ratably over the course of a service period, as appropriate, such as in the case of ongoing research and development activities.
	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 Company had deferred research and development advance payments of approximately $0.2 million as of December 31, 2012. The deferred research and development advance payments were 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 grant and collaboration 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 and preferred stock that include a put feature, 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 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, 2013.
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.
	Prior to becoming a public company, the Company utilized various valuation methodologies in accordance with the framework of the 2004 American Institute of Certified Public Accountants Technical Practice Aid, Valuation of Privately-Held Company Equity Securities Issued as Compensation, to estimate the fair value of its stock. The methodologies included an option pricing method to estimate the Company's underlying equity value, and a methodology that determined an estimated value under an initial public offering (IPO) scenario and a sale scenario based upon an assessment of the probability of occurrence of each scenario. Each valuation methodology included estimates and assumptions that required the Company's judgment. These estimates included assumptions regarding future performance, including the completion of clinical trials and the time to complete an IPO or sale of the Company. As with any valuation, significant changes to the key assumptions used in the valuations could result in different fair values of common stock at each valuation date.
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 (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.

Summary_of_significant_account2

Summary of significant accounting policies (Tables)	12 Months Ended
	Dec. 31, 2013
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, 2013
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, 2013
		Total			Quoted prices in		Significant			Significant
					active markets for		other			unobservable
					identical assets		observable			inputs
					(level 1)		inputs			(level 3)
							(level 2)
	Marketable securities	$	127,053,124		$	—	$	127,053,124		$	—
	Warrant liability	$	58,154		$	—	$	—		$	58,154
		December 31, 2012
		Total			Quoted prices in		Significant			Significant
					active markets for		other			unobservable
					identical assets		observable			inputs
					(level 1)		inputs			(level 3)
							(level 2)
	Warrant liability	$	95,661		$	—	$	—		$	95,661
Summary of marketable securities accounted for as available-for-sale securities	'
		December 31, 2013
					Gross Unrealized
		Amortized								Fair
		Cost			Gains		Losses			Value
	Commercial paper	$	14,993,309		$	5,151	$	—		$	14,998,460
	U.S. corporate debt securities		111,989,422			96,737		(31,495	)		112,054,664
		$	126,982,731		$	101,888	$	(31,495	)	$	127,053,124
Schedule of marketable securities on the balance sheet	'
		December 31, 2013
		Less Than			More Than
		12 Months			12 Months
	Commercial paper	$	14,998,460		$	—
	U.S. corporate debt securities		54,158,359			57,896,305
	Total Marketable securities	$	69,156,819		$	57,896,305
Summary of changes in the fair value of the Company's Level 3 valuation for warrant liability	'
		Level 3 assets
	Beginning balance January 1, 2012	$	1,878,316
	Change in fair value of warrant liability		(1,782,655	)
	Ending balance as of December 31, 2012	$	95,661
	Change in fair value of warrant liability		(37,507	)
	Ending balance as of December 31, 2013	$	58,154

Fixed_assets_Tables

Fixed assets (Tables)	12 Months Ended
	Dec. 31, 2013
Fixed assets	'
Schedule of fixed assets, net	'
		December 31,
		2013			2012
	Leasehold improvements	$	12,473,836		$	12,473,836
	Computer equipment and software		2,284,836			2,118,713
	Furniture, fixtures, and lab equipment		14,283,875			13,969,758
	Assets not yet placed in service		369,644			4,152
			29,412,191			28,566,459
	Less accumulated depreciation and amortization		(22,682,827	)		(20,286,422	)
		$	6,729,364		$	8,280,037

Accounts_payable_and_accrued_e1

Accounts payable and accrued expenses (Tables)	12 Months Ended
	Dec. 31, 2013
Accounts payable and accrued expenses	'
Schedule of components of accounts payable and accrued expenses	'
		December 31,
		2013		2012
	Employee compensation, benefits, and related accruals	$	5,102,795	$	3,096,475
	Consulting and contracted research		4,006,336		2,515,678
	Professional fees		1,294,637		559,228
	Accounts payable		1,123,895		621,591
	Other		679,720		230,999
		$	12,207,383	$	7,023,971

Capital_structure_Tables

Capital structure (Tables)	12 Months Ended
	Dec. 31, 2013
Capital structure	'
Summary of the Company's outstanding warrants	'
	The following is a summary of the Company's outstanding warrants as of December 31, 2013:
		Warrant shares		Exercise price		Expiration
	Common stock		1,428	$	128		2014
	Common stock		6,250	$	128		2017
	Common stock		7,030	$	128		2019 and 2020
	Common stock		452	$	2,520.00		2014
	The following is a summary of the Company's outstanding warrants as of December 31, 2012:
		Warrant shares		Exercise price		Expiration
	Series Two		24,712	$	16		2014
	Series Two		50,000	$	16		2017
	Series Two		56,250	$	16		2019 and 2020
	Common stock		645	$	2,520		2013 and 2014

Earnings_per_share_Tables

Earnings per share (Tables)	12 Months Ended
	Dec. 31, 2013
Earnings per share	'
Schedule of computation of basic and diluted earnings per share for common stockholders	'
		Year ended December 31
		2013			2012			2011
	Numerator
	Net (loss) income	$	(51,573,575	)	$	(26,235,102	)	$	30,904,514
	Deemed dividend		(18,248,768	)		—			—
	Gain on exchange of convertible preferred stock in connection with recapitalization		3,390,750			159,954,069			—
	Less beneficial conversion charge		—			(377,787	)		—
	Less net income attributable to participating preferred stock		—			(132,609,918	)		(30,878,445	)
	Net (loss) income attributable to common stockholders	$	(66,431,593	)	$	731,262		$	26,069
	Denominator
	Denominator for basic earnings per share		12,829,411			3,328			1,089
	Effect of dilutive securities:
	Employee stock options		—			—			4,640
	Series 3 convertible preferred stock		—			13,877			—
	Denominator for diluted earnings per share		12,829,411			17,205			5,729
	Net (loss) income per share:
	Basic		(5.18	)		219.76			23.95
	Diluted		(5.18	)		42.5			4.55

Stock_option_plan_Tables

Stock option plan (Tables)	12 Months Ended
	Dec. 31, 2013
Stock option plan	'
Summary of stock option activity	'
		Number of			Exercise price			Weighted-			Weighted-		Aggregate
		options						average			average		intrinsic
								exercise			remaining		value
								price			contractual
											term
	Outstanding at December 31, 2010		39,557		$	226.80 - $1,149.60		$	547.2
	Granted		8,123		$	490.8		$	490.8
	Exercised		(11	)	$	451.20 - $508.80		$	459.6
	Forfeited		(875	)	$	226.80 - $1,149.60		$	757.2
	Outstanding at December 31, 2011		46,794		$	226.80 - $1,149.60		$	532.8			5.74 years
	Granted		5,715		$	218.4		$	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	$	11,905,903
	Vested or expected to vest at December 31, 2013		1,971,286					$	20.78			9.28 years	$	11,209,761
	Exercisable at December 31, 2013		146,340					$	129.81			7.90 years	$	688,971
Schedule of assumptions used to estimate fair value of grants made on the date of grant	'
		2013			2012			2011
	Risk-free interest rate		0.85 - 1.90	%		1.14	%		2.4	%
	Expected volatility		87 - 89	%		87	%		87	%
	Expected term		6.00 - 6.25 years			6.00 - 6.25 years			6.00 - 6.25 years
Summary of stock options outstanding and exercisable	'
		Outstanding
											Exercisable
								Weighted-Average
								Remaining
								Contractual
	Range of Exercise Price	Number of			Weighted-Average			Life (in years)			Number of		Weighted Average
		Options			Exercise						Options		Exercise Price
					Price
	$10.59 - $10.85		1,945,213		$	10.85			9.37			109,113	$	10.84
	$10.85 - $20.76		109,400		$	19.43			9.87			—	$	—
	$20.76 - $490.80		28,226		$	311.28			3.75			24,676	$	309.97
	$490.80 - 735.60		8,964		$	673.95			3.87			8,966	$	673.95
	$1,149.60		3,789		$	1,149.60			6.01			3,585	$	1,149.60
			2,095,592									146,340
Summary of information on the Company's restricted stock	'
		Restricted Stock
		Number of			Weighted
		Shares			Average Grant
					Date Fair
					Value
	January 1, 2013		—			—
	Granted		1,131,524		$	10.68
	Vested		—		$	—
	Forfeited		(21,298	)	$	10.65
	Unvested at December 31, 2013		1,110,226		$	10.68
Schedule of share-based compensation expense recorded in the statement of operations	'
		Year ended December 31,
		2013			2012			2011
	Research and development	$	2,039,880		$	804,576		$	916,495
	General and administrative		6,387,308			1,483,816			1,900,142
	Total	$	8,427,188		$	2,288,392		$	2,816,637

Other_comprehensive_income_los1

Other comprehensive income (loss) and accumulated other comprehensive items (Tables)	12 Months Ended
	Dec. 31, 2013
Other comprehensive income (loss) and accumulated other comprehensive items	'
Summary of other comprehensive income (loss) and the changes in accumulated other comprehensive items, by component	'
		Unrealized			Total Accumulated
		Gains On			Other
		Marketable			Comprehensive
		Securities			Items
	Balance at January 1, 2011	$	3,606		$	3,606
	Other comprehensive loss before reclassifications		(3,606	)		(3,606	)
	Amounts reclassified from other comprehensive items		—			—
	Other comprehensive income/(loss)		—			—
	Balance at December 31, 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		70,393			70,393
	Amounts reclassified from other comprehensive items		—			—
	Other comprehensive income		70,393			70,393
	Balance at December 31, 2013	$	70,393		$	70,393

Income_taxes_Tables

Income taxes (Tables)	12 Months Ended
	Dec. 31, 2013
Income taxes	'
Schedule of reconciliation of the U.S. statutory income tax rate to the Company's effective tax rate	'
					December 31,
		2013			2012			2011
	Federal income tax (benefit) at statutory rate		34	%		34	%		34	%
	State income tax benefit, net of federal benefit		5.65			3.8			4.2
	Permanent differences		(5.90	)		—			—
	Research and development		15.88			—			—
	Increase to valuation allowance		(49.63	)		(35.80	)		(45.90	)
	Other		—			(2.00	)		(1.60	)
	Effective income tax rate		0	%		0	%		(9.30	)%
Schedule of significant components of the Company's deferred tax assets and liabilities	'
		2013			2012
	Deferred tax assets:
	Amortization	$	80,387		$	91,871
	Depreciation		1,922,332			1,535,952
	Accrued expense		332,539			1,208,846
	Deferred revenue		350,447			6,962,506
	Federal tax credits		14,081,615			5,383,092
	State tax credits		1,587,217			1,094,833
	Federal net operating losses		88,187,475			71,752,278
	State net operating losses		10,456,688			7,619,606
	Capitalized research and development costs		12,254,381			10,479,055
	Other		3,211,720			742,341
	Total gross deferred tax assets		132,464,801			106,870,380
	Less valuation allowance		(132,464,801	)		(106,870,380	)
	Net deferred tax assets	$	—		$	—

Commitments_and_contingencies_

Commitments and contingencies (Tables)	12 Months Ended
	Dec. 31, 2013
Commitments and contingencies	'
Schedule of future minimum lease payments	'
	Future minimum lease payments as of December 31, 2013 are as follows:
	2014	$	890,000
	2015		849,000
	2016		849,000
	2017		849,000
	2018		952,000
	Thereafter		162,000
		$	4,551,000

Selected_quarterly_financial_d1

Selected quarterly financial data (Tables)	12 Months Ended
	Dec. 31, 2013
Selected quarterly financial data	'
Summary of quarterly data	'
		For the quarters ending
		March 31			June 30			September 30			December 31
	2013:00:00
	Collaboration and grant revenue	$	7,141,664		$	6,854,212		$	16,289,573		$	4,410,878
	Operating expenses		15,718,073			21,307,148			20,565,188			22,503,387
	Loss from operations		(8,576,409	)		(14,452,936	)		(4,275,615	)		(18,092,509	)
	Net loss		(14,684,535	)		(14,586,578	)		(4,416,499	)		(17,885,963	)
	Deemed dividend		(18,248,768	)		—			—			—
	Gain on exchange of convertible preferred stock in connection with recapitalization		3,390,750			—			—			—
	Net loss attributable to common stockholders		(29,542,553	)		(14,586,578	)		(4,416,499	)		(17,885,963	)
	Basic net loss per common share(1)	$	(6,527.30	)	$	(5.51	)	$	(0.19	)	$	(0.75	)
	Diluted net loss per common share(1)	$	(6,527.30	)	$	(5.51	)	$	(0.19	)	$	(0.75	)
	2012:00:00
	Collaboration and grant revenue	$	12,525,720		$	7,585,177		$	7,195,076		$	6,640,090
	Operating expenses		18,745,957			15,083,384			14,250,383			12,674,520
	Loss from operations		(6,220,237	)		(7,498,207	)		(7,055,307	)		(6,034,430	)
	Net loss		(6,597,861	)		(6,068,072	)		(7,297,125	)		(6,272,044	)
	Gain on exchange of convertible preferred stock in connection with recapitalization		—			159,954,069			—			—
	Less beneficial conversion charge		—			(377,787	)		—			—
	Net income (loss) attributable to common stockholders		(6,597,861	)		153,508,210			(7,297,125	)		(6,272,044	)
	Basic net income (loss) per common share(1)	$	(5,992.61	)	$	168		$	(1,605.53	)	$	(1,380.13	)
	Diluted net income (loss) per common share(1)	$	(5,992.61	)	$	48.29		$	(1,605.53	)	$	(1,380.13	)
	-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 $)	Dec. 31, 2013	Dec. 31, 2012
The Company	'	'
Accumulated deficit	$328,798,293	$277,224,718

Summary_of_significant_account3

Summary of significant accounting policies (Details)	12 Months Ended
	Dec. 31, 2013
	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 2)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Concentration of risks	'	'	'
Number of largest collaboration partners	2	'	'
Revenue | Customer concentration risk | Collaboration partner one	'	'	'
Concentration of risks	'	'	'
Concentration risk (as a percent)	80.00%	67.00%	85.00%
Revenue | Customer concentration risk | Collaboration partner two	'	'	'
Concentration of risks	'	'	'
Concentration risk (as a percent)	10.00%	11.00%	8.00%
Revenue | Customer concentration risk | Granting agency	'	'	'
Concentration of risks	'	'	'
Concentration risk (as a percent)	8.00%	9.00%	3.00%

Summary_of_significant_account5

Summary of significant accounting policies (Details 3) (USD $)	3 Months Ended	12 Months Ended		0 Months Ended
	Jun. 30, 2012	Dec. 31, 2013	Dec. 31, 2012	Mar. 07, 2013
				Common stock
Reverse stock split	'	'	'	'
Reverse stock split ratio	'	'	'	0.0083
Research and development costs	'	'	'	'
Deferred research and development advance payments	'	'	$200,000	'
Beneficial conversion	'	'	'	'
Beneficial conversion charge	377,787	'	377,787	'
Impairment of long-lived assets	'	'	'	'
Impairment of long-lived assets	'	$0	'	'

Fair_value_of_financial_instru2

Fair value of financial instruments and investments (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Financial assets and liabilities measured at fair value on recurring basis	'	'
Marketable securities	$127,053,124	'
Recurring basis | Total	'	'
Financial assets and liabilities measured at fair value on recurring basis	'	'
Marketable securities	127,053,124	'
Warrant liability	58,154	95,661
Recurring basis | Significant other observable inputs (level 2)	'	'
Financial assets and liabilities measured at fair value on recurring basis	'	'
Marketable securities	127,053,124	'
Recurring basis | Significant unobservable inputs (level 3)	'	'
Financial assets and liabilities measured at fair value on recurring basis	'	'
Warrant liability	$58,154	$95,661

Fair_value_of_financial_instru3

Fair value of financial instruments and investments (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2013
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	126,982,731
Gross Unrealized Gains	101,888
Gross Unrealized Losses	-31,495
Total Marketable securities	127,053,124
Commercial paper	'
Marketable securities accounted for as available-for-sale securities	'
Amortized Cost	14,993,309
Gross Unrealized Gains	5,151
Total Marketable securities	14,998,460
U.S. corporate debt securities	'
Marketable securities accounted for as available-for-sale securities	'
Amortized Cost	111,989,422
Gross Unrealized Gains	96,737
Gross Unrealized Losses	-31,495
Total Marketable securities	$112,054,664

Fair_value_of_financial_instru4

Fair value of financial instruments and investments (Details 3) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Marketable securities on the balance sheet	'	'
Total Marketable securities, Less Than 12 Months	$69,156,819	'
Total Marketable securities, More Than 12 Months	57,896,305	'
Marketable securities	'	0
Commercial paper	'	'
Marketable securities on the balance sheet	'	'
Total Marketable securities, Less Than 12 Months	14,998,460	'
U.S. corporate debt securities	'	'
Marketable securities on the balance sheet	'	'
Total Marketable securities, Less Than 12 Months	54,158,359	'
Total Marketable securities, More Than 12 Months	$57,896,305	'

Fair_value_of_financial_instru5

Fair value of financial instruments and investments (Details 4) (USD $)	Jun. 30, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2012
	Common stock	Warrant	Warrant	Warrant	Warrant	Warrant	Warrant	Warrant	Warrant
				Minimum	Minimum	Maximum	Maximum	Common stock	Preferred shares
Changes in the fair value of warrant liability	'	'	'	'	'	'	'	'	'
Beginning balance	'	$95,661	$1,878,316	'	'	'	'	'	'
Change in fair value of warrant liability	'	-37,507	-1,782,655	'	'	'	'	'	'
Ending balance	'	$58,154	$95,661	'	'	'	'	'	'
Assumption used to estimate the fair value of warrant liability by utilizing the Black-Scholes option-pricing model	'	'	'	'	'	'	'	'	'
Volatility (as a percent)	'	'	87.00%	61.00%	'	89.00%	'	'	'
Risk-free interest rate (as a percent)	'	'	'	0.07%	0.16%	2.10%	1.18%	'	'
Strike price (in dollars per share)	'	'	$16	$128	'	$2,520	'	'	'
Fair value of shares (in dollars per share)	$15	'	'	'	'	'	'	$16.97	$2.35
Expected life	'	'	'	'3 months 18 days	'1 year	'5 years 8 months 12 days	'7 years	'	'

Fixed_assets_Details

Fixed assets (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Fixed assets	'	'	'
Gross fixed assets	$29,412,191	$28,566,459	'
Less accumulated depreciation and amortization	-22,682,827	-20,286,422	'
Net fixed assets	6,729,364	8,280,037	'
Depreciation expense	2,396,405	2,704,151	2,871,200
Leasehold improvements	'	'	'
Fixed assets	'	'	'
Gross fixed assets	12,473,836	12,473,836	'
Computer equipment and software	'	'	'
Fixed assets	'	'	'
Gross fixed assets	2,284,836	2,118,713	'
Furniture, fixtures, and lab equipment	'	'	'
Fixed assets	'	'	'
Gross fixed assets	14,283,875	13,969,758	'
Assets not yet placed in service	'	'	'
Fixed assets	'	'	'
Gross fixed assets	$369,644	$4,152	'

Accounts_payable_and_accrued_e2

Accounts payable and accrued expenses (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Accounts payable and accrued expenses	'	'
Employee compensation, benefits, and related accruals	$5,102,795	$3,096,475
Consulting and contracted research	4,006,336	2,515,678
Professional fees	1,294,637	559,228
Accounts payable	1,123,895	621,591
Other	679,720	230,999
Accounts payable and accrued expenses	$12,207,383	$7,023,971

Longterm_debt_Details

Long-term debt (Details) (Laboratory instrument, USD $)	Dec. 31, 2013	Dec. 31, 2012	31-May-09
In Millions, unless otherwise specified
Laboratory instrument	'	'	'
Capital lease information	'	'	'
Implied interest rate (as a percent)	'	'	8.20%
Remaining principal	$0.10	$0.20	'

Longterm_debt_Details_2

Long-term debt (Details 2) (Secured debt facility, USD $)	1 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2009
	item
Secured debt facility	'
Debt	'
Maximum borrowing capacity	$25
Number of lenders	2

Longterm_debt_Details_3

Long-term debt (Details 3) (USD $)	1 Months Ended	12 Months Ended		1 Months Ended		12 Months Ended
	Jul. 31, 2013	Dec. 31, 2013	Dec. 31, 2011	Dec. 31, 2010	Sep. 30, 2009	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2009
			Series F-2 convertible preferred stock	Secured debt facility	Secured debt facility	Secured debt facility	Secured debt facility	Secured debt facility
			Warrants					Series F-2 convertible preferred stock
								Warrants
Long-term debt	'	'	'	'	'	'	'	'
Number of shares purchased through warrants	'	'	'	'	'	'	'	62,500
Exercise price (in dollars per share)	'	'	'	'	'	'	'	$16
Amount borrowed	'	'	'	$10,000,000	$12,500,000	'	'	'
Fixed interest rate of notes (as a percent)	'	'	'	'	'	13.65%	'	'
Period of interest-only payments	'	'	'	'	'	'5 months	'	'
Period for principal repayment	'	'	'	'	'	'30 months	'	'
Number of shares that can be acquired from warrants exercisable	'	'	56,250	'	'	'	'	'
Outstanding balance of the notes	'	'	'	'	'	'	4,800,000	'
Paid outstanding principal and interest, due under promissory notes issued	2,600,000	'	'	'	'	'	'	'
Loss on extinguishment of debt	'	($129,963)	'	'	'	'	'	'

Capital_structure_Details

Capital structure (Details) (USD $)

1 Months Ended

3 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

1 Months Ended

Jul. 31, 2012

Mar. 31, 2013

Jun. 30, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2011

Dec. 31, 2011

Dec. 31, 2011

Dec. 31, 2011

Dec. 31, 2011

Dec. 31, 2011

Dec. 31, 2011

Dec. 31, 2011

Dec. 31, 2011

Dec. 31, 2011

Dec. 31, 2011

Dec. 31, 2011

Jul. 31, 2012

Dec. 31, 2012

Dec. 31, 2012

Dec. 31, 2012

item

Maximum

Minimum

Series A

Series B

Series C

Series D

Series E

Series E-2

Series F

Series F-2

Series G

Series F, F-2 and G

Series One

Series One

Series Two

Series Three

Minimum

item

item

item

Capital structure

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Shares authorized

'

'

'

'

'

'

156,995,095

'

750,000

187,500

6,295,000

13,769,935

126,735,022

3,670,138

675,000

1,612,500

3,300,000

'

'

2,000,000

13,750,000

13,750,000

Par value (in dollars per share)

'

'

'

'

'

$0.00

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Conversion factor

'

'

'

'

'

'

'

'

0.0833

0.1333

0.1389

0.1548

0.0548

1

1

1

1

'

'

'

'

'

Percentage of the outstanding preferred shares on an as-converted to common stock basis

'

'

'

'

'

'

'

66.67%

'

'

'

'

'

'

'

'

'

66.67%

'

'

'

'

Number of members of board of directors who can be elected by holders of the preferred stock, voting as a single class

'

'

'

'

'

6

'

'

'

'

'

'

'

'

'

'

'

'

'

12

'

'

Liquidation preference (in dollars per share)

'

'

'

'

'

'

'

'

$1

$2

$2.50

$3.25

$0.40

$7.26

$16

$16

$16

'

'

'

'

'

Aggregate liquidation preference

'

'

'

'

'

'

'

'

$800,000

$400,000

$15,000,000

$42,600,000

$50,000,000

$26,600,000

$10,000,000

$24,200,000

$50,300,000

'

'

'

'

'

Issuance of common stock from IPO and exercise of over allotment exercise, net of offering costs (in shares)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,483,337

'

'

'

Aggregate gross proceeds

'

'

'

'

29,354,752

'

'

'

'

'

'

'

'

'

'

'

'

'

29,700,000

'

'

'

Gain on exchange of convertible preferred stock in connection with recapitalization

$160,000,000

$3,390,750

$159,954,069

$3,390,750

$159,954,069

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Original issuance price multiplier

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2

'

'

Assets available for distribution to series two convertible preferred stock, distribution percentage

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

23.53%

76.47%

'

Stated liquidation preference amount multiplier

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1

1

Assets available for distribution to series three convertible preferred stock, distribution percentage

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

23.53%

67.65%

8.82%

Remaining assets distribution percentage

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

20.00%

55.00%

25.00%

Shares issued upon conversion of preferred stock multiplier

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

5

'

'

Number of shares issued for each share of convertible preferred stock upon conversion

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2

1

1

Capital_structure_Details_2

Capital structure (Details 2) (USD $)

1 Months Ended

3 Months Ended

12 Months Ended

0 Months Ended

0 Months Ended

1 Months Ended

0 Months Ended

1 Months Ended

3 Months Ended

0 Months Ended

Jul. 31, 2012

Mar. 31, 2013

Jun. 30, 2012

Dec. 31, 2013

Dec. 31, 2012

Mar. 07, 2013

Feb. 28, 2013

Mar. 07, 2013

31-May-13

Mar. 07, 2013

Mar. 07, 2013

Mar. 07, 2013

Jun. 30, 2013

Dec. 31, 2013

Jun. 30, 2013

Mar. 31, 2013

Feb. 28, 2013

Mar. 07, 2013

Series One and Series Two

Series One and Series Two

Series Four

Series Four

Series Five

Series Five

Common stock

Common stock

Series Four and Series Five Convertible Preferred Stock

Series Four and Series Five Convertible Preferred Stock

Convertible promissory notes

Convertible promissory notes

Convertible promissory notes

Warrants

Warrants

Warrants

Series Four

Capital structure

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Principal amount of convertible promissory notes issued

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$6,000,000

'

Warrants issued to purchase shares

'

'

'

'

'

'

2,527,675

'

'

'

'

'

'

'

'

'

'

'

Exercise price (in dollars per share)

'

'

'

'

'

'

$0.01

'

'

'

'

'

'

'

'

'

'

'

Debt discount recorded to interest expense

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

6,000,000

'

'

Shares issued and sold

'

'

'

'

'

2,527,675

'

4,497,035

375,000

'

'

'

9,627,800

'

'

'

'

'

Aggregate gross proceeds

'

'

'

'

29,354,752

'

'

54,000,000

'

'

'

'

'

'

'

'

'

'

Amount raised in bridge financing

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

6,000,000

'

'

Gross proceeds raised

'

60,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Shares issued upon conversion of convertible promissory notes

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

502,919

Reverse stock split ratio

'

'

'

'

'

'

'

'

'

'

'

0.0083

'

'

'

'

'

'

Number of shares issued upon conversion

'

'

'

'

'

'

'

'

'

6,700,487

2,095,515

'

'

'

14,170,956

'

'

'

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

160,000,000

3,390,750

159,954,069

3,390,750

159,954,069

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of shares issuable upon conversion of each stock

'

'

'

'

'

'

'

'

'

'

'

'

'

1

'

'

'

'

Share price (in dollars per share)

'

'

'

'

'

'

'

'

$12

'

'

'

$15

'

'

'

'

'

Aggregate purchase price

'

'

'

131,649,688

'

'

'

'

4,500,000

'

'

'

'

'

'

'

'

'

Common stock

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Common stock, authorized shares

'

'

'

125,000,000

17,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

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

'

'

'

'

'

'

'

'

'

'

'

'

1,255,800

'

'

'

'

'

Net proceeds from initial public offering

'

'

'

$131,649,688

'

'

'

'

'

'

'

'

$131,600,000

'

'

'

'

'

Number of shares issued upon conversion

'

'

'

'

'

'

'

'

'

6,700,487

2,095,515

'

'

'

14,170,956

'

'

'

Capital_structure_Details_3

Capital structure (Details 3) (Warrants, USD $)	Dec. 31, 2013	Dec. 31, 2012
Common stock | 2014	'	'
Warrants	'	'
Warrant shares	1,428	'
Exercise price (in dollars per share)	$128	'
Common stock | 2017	'	'
Warrants	'	'
Warrant shares	6,250	'
Exercise price (in dollars per share)	$128	'
Common stock | 2019 and 2020	'	'
Warrants	'	'
Warrant shares	7,030	'
Exercise price (in dollars per share)	$128	'
Common stock | 2014	'	'
Warrants	'	'
Warrant shares	452	645
Exercise price (in dollars per share)	$2,520	$2,520
Series Two | 2014	'	'
Warrants	'	'
Warrant shares	'	24,712
Exercise price (in dollars per share)	'	$16
Series Two | 2017	'	'
Warrants	'	'
Warrant shares	'	50,000
Exercise price (in dollars per share)	'	$16
Series Two | 2019 and 2020	'	'
Warrants	'	'
Warrant shares	'	56,250
Exercise price (in dollars per share)	'	$16

Earnings_per_share_Details

Earnings per share (Details) (USD $)

1 Months Ended

3 Months Ended

12 Months Ended

Jul. 31, 2012

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Net (loss) income 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) income

'

($17,885,963)

($4,416,499)

($14,586,578)

($14,684,535)

($6,272,044)

($7,297,125)

($6,068,072)

($6,597,861)

($51,573,575)

($26,235,102)

$30,904,514

Deemed dividend

'

'

'

'

18,248,768

'

'

'

'

18,248,768

'

'

Gain on exchange of convertible preferred stock in connection with recapitalization

160,000,000

'

'

'

3,390,750

'

'

159,954,069

'

3,390,750

159,954,069

'

Less beneficial conversion charge

'

'

'

'

'

'

'

-377,787

'

'

-377,787

'

Less net income attributable to participating preferred stock

'

'

'

'

'

'

'

'

'

'

-132,600,000

-30,900,000

Net (loss) income attributable to common stockholders

'

'

'

'

'

'

'

'

'

($66,431,593)

$731,262

$26,069

Denominator

'

'

'

'

'

'

'

'

'

'

'

'

Denominator for basic earnings per share (in shares)

'

'

'

'

'

'

'

'

'

12,829,411

3,328

1,089

Effect of dilutive securities:

'

'

'

'

'

'

'

'

'

'

'

'

Employee stock options (in shares)

'

'

'

'

'

'

'

'

'

'

'

4,640

Series 3 convertible preferred stock (in shares)

'

'

'

'

'

'

'

'

'

'

13,877

'

Denominator for diluted earnings per share (in shares)

'

'

'

'

'

'

'

'

'

12,829,411

17,205

5,729

Net (loss) income per share:

'

'

'

'

'

'

'

'

'

'

'

'

Basic (in dollars per share)

'

($0.75)

($0.19)

($5.51)

($6,527.30)

($1,380.13)

($1,605.53)

$168

($5,992.61)

($5.18)

$219.76

$23.95

Diluted (in dollars per share)

'

($0.75)

($0.19)

($5.51)

($6,527.30)

($1,380.13)

($1,605.53)

$48.29

($5,992.61)

($5.18)

$42.50

$4.55

Stock_option_plan_Details

Stock option plan (Details) (USD $)

12 Months Ended

1 Months Ended

12 Months Ended

0 Months Ended

1 Months Ended

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

31-May-13

Dec. 31, 2013

Dec. 31, 2013

Mar. 05, 2013

Mar. 05, 2013

Mar. 05, 2013

Mar. 05, 2013

31-May-13

Dec. 31, 2013

31-May-13

31-May-13

Stock options

Stock options

Stock options

Stock options

Stock options

Stock options

Stock options

Stock options

Stock options

Restricted stock

2009 Stock Incentive Plan

2009 Stock Incentive Plan

2009 Stock Incentive Plan

2013 Stock Incentive Plan

2013 Stock Incentive Plan

2013 Stock Incentive Plan

2013 Stock Incentive Plan

2009 Equity and Long Term Incentive Plan and 2013 Stock Incentive Plan

2013 Long Term Incentive Plan

2013 Long Term Incentive Plan

2013 Long Term Incentive Plan

Minimum

Minimum

Minimum

Maximum

Maximum

Maximum

Stock options

Stock options

Stock options

Restricted stock

Common stock

Common stock

Common stock

Common stock

Common stock

Minimum

Maximum

Minimum

Maximum

Stock option plan

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of shares authorized

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

739,937

'

'

'

'

Number of shares of restricted stock granted

'

'

'

'

'

'

'

'

'

1,131,524

'

'

'

'

4,613

735,324

'

'

'

'

'

Number of shares available for issuance

'

'

'

'

'

'

'

'

'

'

'

'

'

0

'

'

'

122,296

96,917

'

'

Number of additional shares authorized

'

'

'

'

'

'

'

'

'

'

2,500,000

'

'

'

'

'

'

'

'

'

'

Number of shares subject to outstanding awards

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

3,040,444

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%

'

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%

'

'

'

'

'

'

'

'

'

Expiration period

'

'

'

'

'

'

'

'

'

'

'

'

'10 years

'

'

'

'

'

'

'

'

Vesting period

'

'

'

'3 years

'

'

'4 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of options

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Outstanding at the beginning of the period (in shares)

42,394

46,794

39,557

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Granted (in shares)

2,117,113

5,715

8,123

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Exercised (in shares)

'

'

-11

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Forfeited (in shares)

-63,915

-10,115

-875

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Outstanding at the end of the period (in shares)

2,095,592

42,394

46,794

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Vested or expected to vest at the end of the period (in shares)

1,971,286

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Exercisable at the end of the period (in shares)

146,340

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Exercise price

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Outstanding at the beginning of the period (in dollars per share)

'

'

'

$218.40

$226.80

$226.80

$1,149.60

$1,149.60

$1,149.60

'

'

'

'

'

'

'

'

'

'

'

'

Granted (in dollars per share)

'

$218.40

$490.80

$10.59

'

'

$20.76

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Exercised (in dollars per share)

'

'

'

'

'

$451.20

'

'

$508.80

'

'

'

'

'

'

'

'

'

'

'

'

Forfeited (in dollars per share)

'

'

'

$10.85

$218.40

$226.80

$1,149.60

$1,149.60

$1,149.60

'

'

'

'

'

'

'

'

'

'

'

'

Outstanding at the end of the period (in dollars per share)

'

'

'

$10.59

$218.40

$226.80

$1,149.60

$1,149.60

$1,149.60

'

'

'

'

'

'

'

'

'

'

'

'

Weighted-average exercise price

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Outstanding at the beginning of the period (in dollars per share)

$474

$532.80

$547.20

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Granted (in dollars per share)

$11.29

$218.40

$490.80

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Exercised (in dollars per share)

'

'

$459.60

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Forfeited (in dollars per share)

$12.57

$604.80

$757.20

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Outstanding at the end of the period (in dollars per share)

$20.24

$474

$532.80

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Vested or expected to vest at the end of the period (in dollars per share)

$20.78

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Exercisable at the end of the period (in dollars per share)

$129.81

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Weighted-average remaining contractual term

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Outstanding at the end of the period

'9 years 3 months 14 days

'5 years 7 days

'5 years 8 months 26 days

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Vested or expected to vest at the end of the period

'9 years 3 months 11 days

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Exercisable at the end of the period

'7 years 10 months 24 days

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Valuation assumptions

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Risk-free interest rate (as a percent)

'

1.14%

2.40%

0.85%

'

'

1.90%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Expected volatility (as a percent)

'

87.00%

87.00%

87.00%

'

'

89.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Expected term

'

'

'

'6 years

'6 years

'6 years

'6 years 3 months

'6 years 3 months

'6 years 3 months

'

'

'

'

'

'

'

'

'

'

'

'

Expected dividend yield (as a percent)

0.00%

0.00%

0.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Weighted average grant date fair value (in dollars per share)

$8.23

$160.65

$364.80

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Aggregate intrinsic value

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Outstanding at the end of the period (in dollars)

$11,905,903

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Vested or expected to vest at the end of the period (in dollars)

11,209,761

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Exercisable at the end of the period (in dollars)

$688,971

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Stock_option_plan_Details_2

Stock option plan (Details 2) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2013
Stock options outstanding and exercisable	'
Outstanding, Number of options (in shares)	2,095,592
Exercisable, Number of options (in shares)	146,340
Additional compensation recognized due to modifications to the options granted	$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)	1,945,213
Outstanding, Weighted-Average Exercise Price (in dollars per share)	$10.85
Outstanding, Weighted-Average Remaining Contractual Life	'9 years 4 months 13 days
Exercisable, Number of options (in shares)	109,113
Exercisable, Weighted-Average Exercise Price (in dollars per share)	$10.84
$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)	109,400
Outstanding, Weighted-Average Exercise Price (in dollars per share)	$19.43
Outstanding, Weighted-Average Remaining Contractual Life	'9 years 10 months 13 days
$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)	$490.80
Outstanding, Number of options (in shares)	28,226
Outstanding, Weighted-Average Exercise Price (in dollars per share)	$311.28
Outstanding, Weighted-Average Remaining Contractual Life	'3 years 9 months
Exercisable, Number of options (in shares)	24,676
Exercisable, Weighted-Average Exercise Price (in dollars per share)	$309.97
$490.80-735.60	'
Stock options outstanding and exercisable	'
Range of Exercise Price, Lower (in dollars per share)	$490.80
Range of Exercise Price, Higher (in dollars per share)	$735.60
Outstanding, Number of options (in shares)	8,964
Outstanding, Weighted-Average Exercise Price (in dollars per share)	$673.95
Outstanding, Weighted-Average Remaining Contractual Life	'3 years 10 months 13 days
Exercisable, Number of options (in shares)	8,966
Exercisable, Weighted-Average Exercise Price (in dollars per share)	$673.95
$1,149.60	'
Stock options outstanding and exercisable	'
Outstanding, Number of options (in shares)	3,789
Outstanding, Weighted-Average Exercise Price (in dollars per share)	$1,149.60
Outstanding, Weighted-Average Remaining Contractual Life	'6 years 4 days
Exercisable, Number of options (in shares)	3,585
Exercisable, Weighted-Average Exercise Price (in dollars per share)	$1,149.60

Stock_option_plan_Details_3

Stock option plan (Details 3) (Restricted stock, USD $)	12 Months Ended
	Dec. 31, 2013
Restricted stock	'
Number of Shares	'
Granted (in shares)	1,131,524
Forfeited (in shares)	-21,298
Balance at the end of the period (in shares)	1,110,226
Weighted Average Grant Date Fair Value	'
Granted (in dollars per share)	$10.68
Forfeited (in dollars per share)	$10.65
Balance at the end of the period (in dollars per share)	$10.68

Stock_option_plan_Details_4

Stock option plan (Details 4) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based compensation expense recorded in the statement of operations	'	'	'
Share-based compensation expense	$8,427,188	$2,288,392	$2,816,637
Unrecognized compensation cost	21,600,000	'	'
Weighted average remaining service period for recognition of unrecognized compensation cost	'2 years 5 months 26 days	'	'
Research and development	'	'	'
Share-based compensation expense recorded in the statement of operations	'	'	'
Share-based compensation expense	2,039,880	804,576	916,495
General and administrative	'	'	'
Share-based compensation expense recorded in the statement of operations	'	'	'
Share-based compensation expense	$6,387,308	$1,483,816	$1,900,142

Other_comprehensive_income_los2

Other comprehensive income (loss) and accumulated other comprehensive items (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2011
Other comprehensive income (loss) and accumulated other comprehensive items	'	'
Balance at the beginning of the period	'	$3,606
Other comprehensive income/(loss) before reclassifications	70,393	-3,606
Other comprehensive income/(loss)	70,393	'
Balance at the end of the period	70,393	'
Unrealized Gains On Marketable Securities	'	'
Other comprehensive income (loss) and accumulated other comprehensive items	'	'
Balance at the beginning of the period	'	3,606
Other comprehensive income/(loss) before reclassifications	70,393	-3,606
Other comprehensive income/(loss)	70,393	'
Balance at the end of the period	$70,393	'

Collaborations_and_grants_Deta

Collaborations and grants (Details) (USD $)

12 Months Ended

1 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

0 Months Ended

12 Months Ended

In Millions, unless otherwise specified

Dec. 31, 2013

Dec. 31, 2013

Aug. 31, 2011

Dec. 31, 2012

Dec. 31, 2011

Jul. 31, 2008

Nov. 30, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Jan. 02, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Minimum

Maximum

Collaboration agreement

Collaboration agreement

Collaboration agreement

Collaboration agreement

Collaboration agreement

Collaboration agreement

Collaboration agreement

Collaboration agreement

Collaboration agreement

Early stage collaboration and discovery agreements

Early stage collaboration and discovery agreements

Early stage collaboration and discovery agreements

Early stage collaboration and discovery agreements

Early stage collaboration and discovery agreements

Early stage collaboration and discovery agreements

Early stage collaboration and discovery agreements

Genzyme

Genzyme

Genzyme

Genzyme

Roche and SMA Foundation

Roche and SMA Foundation

Roche and SMA Foundation

Roche and SMA Foundation

Roche and SMA Foundation

item

Minimum

Maximum

Research and development event milestones

Sales milestones

item

Research and development event milestones

Sales milestones

Maximum

Maximum

Maximum

Collaborations and grants

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Nonrefundable upfront payment received

'

'

$7.50

'

'

$100

$30

'

'

'

'

'

$0.90

$3

'

'

'

'

Selling price of undelivered agreements

'

'

8.8

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Deferred revenue recognized

'

'

79

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Collaboration revenue recognized

'

'

'

3.8

90

'

'

26.6

18.4

'

'

'

4.8

6.6

'

'

'

'

Number of compounds in preclinical development

'

'

'

'

'

'

3

'

'

'

'

'

'

'

'

'

'

'

Number of significant deliverables

'

'

'

'

'

'

2

'

'

'

'

2

'

'

'

'

'

'

Additional consideration receivable upon achievement of specified events

'

'

'

'

'

'

$30

'

'

$135

$325

'

'

'

'

'

$143

$252

Research period for applying technology

'

'

'

'

'

'

'2 years

'

'

'

'

'

'

'

'3 years

'4 years

'

'

Grant revenue

'

'

'

'

'

'

'

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Income_taxes_Details

Income taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
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)	5.65%	3.80%	4.20%
Permanent differences (as a percent)	-5.90%	'	'
Research and development (as a percent)	15.88%	'	'
Increase to valuation allowance (as a percent)	-49.63%	-35.80%	-45.90%
Other (as a percent)	'	-2.00%	-1.60%
Effective income tax rate (as a percent)	0.00%	0.00%	-9.30%
Tax benefit on sale of net operating losses and research and development credits in the New Jersey Transfer Program	'	'	$2,300,000
Deferred tax assets:	'	'	'
Amortization	80,387	91,871	'
Depreciation	1,922,332	1,535,952	'
Accrued expense	332,539	1,208,846	'
Deferred revenue	350,447	6,962,506	'
Federal tax credits	14,081,615	5,383,092	'
State tax credits	1,587,217	1,094,833	'
Federal net operating losses	88,187,475	71,752,278	'
State net operating losses	10,456,688	7,619,606	'
Capitalized research and development costs	12,254,381	10,479,055	'
Other	3,211,720	742,341	'
Total gross deferred tax assets	132,464,801	106,870,380	'
Less valuation allowance	($132,464,801)	($106,870,380)	'

Income_taxes_Details_2

Income taxes (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Income taxes	'	'
Change in valuation allowance	$25,600,000	$9,400,000
Federal	'	'
Operating loss carryforwards	'	'
Net operating loss carryforwards	259,400,000	'
State	'	'
Operating loss carryforwards	'	'
Net operating loss carryforwards	$176,000,000	'

Income_taxes_Details_3

Income taxes (Details 3) (USD $)	Dec. 31, 2013
Federal	'
Credit carryforwards	'
Credit carryforwards	$6,000,000
State	'
Credit carryforwards	'
Credit carryforwards	$2,300,000

Income_taxes_Details_4

Income taxes (Details 4) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating loss carryforwards	'	'	'
U.S. federal income tax rate (as a percent)	34.00%	34.00%	34.00%
Unrecognized income tax benefits	$0	'	'
State | New Jersey	'	'	'
Operating loss carryforwards	'	'	'
Net operating loss carryforwards sold under the Technology Business Tax Certificate Transfer Program	'	'	28.5
Receivable for operating loss carryforwards sold under the Transfer program	'	'	2.3

Commitments_and_contingencies_1

Commitments and contingencies (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Commitments and contingencies	'	'	'
Rent expense	$700,000	$700,000	$700,000
Future minimum lease payments	'	'	'
2014	890,000	'	'
2015	849,000	'	'
2016	849,000	'	'
2017	849,000	'	'
2018	952,000	'	'
Thereafter	162,000	'	'
Total future minimum lease payments	4,551,000	'	'
Funding agreement | Wellcome Trust | Maximum	'	'	'
Other contingencies	'	'	'
Development and regulatory milestone payments which the entity may be obligated to pay	$68,900,000	'	'

401k_plan_Details

401(k) plan (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
401(k) plan	'	'	'
Matching contribution up to the first 5% of employee's base salary (as a percent)	20.00%	'	'
Percentage of employee's base salary, matched by employer	5.00%	'	'
Expense recorded	$0.10	$0.20	$0.20

Selected_quarterly_financial_d2

Selected quarterly financial data (Details) (USD $)	1 Months Ended	3 Months Ended								12 Months Ended
	Jul. 31, 2012	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Selected quarterly financial data	'	'	'	'	'	'	'	'	'	'	'	'
Collaboration and grant revenue	'	$4,410,878	$16,289,573	$6,854,212	$7,141,664	$6,640,090	$7,195,076	$7,585,177	$12,525,720	$34,696,327	$33,946,063	$105,412,147
Operating expenses	'	22,503,387	20,565,188	21,307,148	15,718,073	12,674,520	14,250,383	15,083,384	18,745,957	80,093,796	60,754,244	74,830,150
Loss from operations	'	-18,092,509	-4,275,615	-14,452,936	-8,576,409	-6,034,430	-7,055,307	-7,498,207	-6,220,237	-45,397,469	-26,808,181	30,581,997
Net loss	'	-17,885,963	-4,416,499	-14,586,578	-14,684,535	-6,272,044	-7,297,125	-6,068,072	-6,597,861	-51,573,575	-26,235,102	30,904,514
Deemed dividend	'	'	'	'	-18,248,768	'	'	'	'	-18,248,768	'	'
Gain on exchange of convertible preferred stock in connection with recapitalization	160,000,000	'	'	'	3,390,750	'	'	159,954,069	'	3,390,750	159,954,069	'
Less beneficial conversion charge	'	'	'	'	'	'	'	-377,787	'	'	-377,787	'
Net income (loss) attributable to common stockholders	'	($17,885,963)	($4,416,499)	($14,586,578)	($29,542,553)	($6,272,044)	($7,297,125)	$153,508,210	($6,597,861)	($66,431,593)	$133,341,180	$30,904,514
Basic (in dollars per share)	'	($0.75)	($0.19)	($5.51)	($6,527.30)	($1,380.13)	($1,605.53)	$168	($5,992.61)	($5.18)	$219.76	$23.95
Diluted (in dollars per share)	'	($0.75)	($0.19)	($5.51)	($6,527.30)	($1,380.13)	($1,605.53)	$48.29	($5,992.61)	($5.18)	$42.50	$4.55

Subsequent_events_Details

Subsequent events (Details) (USD $)	12 Months Ended	1 Months Ended			0 Months Ended		1 Months Ended
	Dec. 31, 2013	Dec. 31, 2011	Dec. 31, 2011	Aug. 31, 2013	Feb. 12, 2014	Feb. 12, 2014	Jan. 31, 2014
		Collaboration agreement	Collaboration agreement	Collaboration agreement	Subsequent event	Subsequent event	Subsequent event
		Roche and SMA Foundation	Roche and SMA Foundation	Roche and SMA Foundation		Maximum	Collaboration agreement
		Sales milestones	Sales milestones	Development event milestones			Roche and SMA Foundation
			Maximum				Clinical development milestones
Subsequent events	'	'	'	'	'	'	'
Milestone payments	'	$30,000,000	$460,000,000	$10,000,000	'	'	$7,500,000
Shares issued	'	'	'	'	4,489,796	'	'
Public offering price (in dollars per share)	'	'	'	'	$24.50	'	'
Period of option	'	'	'	'	'30 days	'	'
Common stock shares issuable pursuant to the exercise by the underwriters of an over-allotment option	'	'	'	'	'	673,469	'
Net proceeds from initial public offering	$131,649,688	'	'	'	$118,400,000	'	'