Sarepta Therapeutics (SRPT) 10-Q 8 May 14 2014 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2014	Apr. 30, 2014
Document And Entity Information [Abstract]	'	'
Document Type	'10-Q	'
Amendment Flag	'false	'
Document Period End Date	31-Mar-14	'
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q1	'
Trading Symbol	'SRPT	'
Entity Registrant Name	'Sarepta Therapeutics, Inc.	'
Entity Central Index Key	'0000873303	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Large Accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	40,678,439

Condensed_Consolidated_Balance

Condensed Consolidated Balance Sheets (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current Assets:	'	'
Cash and cash equivalents	$49,101	$256,965
Short-term investments	176,091	'
Accounts receivable	7,849	3,530
Restricted investments	7,250	7,250
Other current assets	9,079	3,061
Total Current Assets	249,370	270,806
Restricted investments, noncurrent	647	647
Property and equipment, net of accumulated depreciation and amortization	20,130	15,049
Patent costs, net of accumulated amortization of $1,740 and $1,622	5,217	5,042
Other assets	25	25
Total Assets	275,389	291,569
Current Liabilities:	'	'
Accounts payable	7,721	8,080
Accrued expenses	16,340	14,601
Current portion of long-term debt	94	92
Warrant liability	9,213	9,006
Deferred revenue	3,303	3,299
Other liabilities	1,087	888
Total Current Liabilities	37,758	35,966
Long-term debt	1,551	1,576
Deferred rent and other long-term liabilities	7,118	6,835
Total Liabilities	46,427	44,377
Commitments and contingencies	'	'
Stockholders' Equity:	'	'
Preferred stock, $.0001 par value, 3,333,333 shares authorized; none issued and outstanding	'	'
Common stock, $.0001 par value, 50,000,000 shares authorized; 37,986,041 and 37,751,920 issued and outstanding at March 31, 2014 and December 31, 2013, respectively	4	4
Additional paid-in capital	800,526	790,424
Accumulated other comprehensive loss	-59	'
Deficit accumulated during the development stage	-571,509	-543,236
Total Stockholders' Equity	228,962	247,192
Total Liabilities and Stockholders' Equity	$275,389	$291,569

Condensed_Consolidated_Balance1

Condensed Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, except Share data, unless otherwise specified
Statement Of Financial Position [Abstract]	'	'
Patent costs, accumulated amortization	$1,740	$1,622
Preferred stock, par value	$0.00	$0.00
Preferred stock, shares authorized	3,333,333	3,333,333
Preferred stock, shares issued	'	'
Preferred stock, shares outstanding	'	'
Common stock, par value	$0.00	$0.00
Common stock, shares authorized	50,000,000	50,000,000
Common stock, issued	37,986,041	37,751,920
Common stock, outstanding	37,986,041	37,751,920

Condensed_Consolidated_Stateme

Condensed Consolidated Statements of Operations and Comprehensive Loss (USD $)	3 Months Ended		404 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014
Income Statement [Abstract]	'	'	'
Revenue from license fees, grants and research contracts	$6,088	$4,474	$193,855
Operating expenses:	'	'	'
Research and development	20,906	13,762	479,483
General and administrative	10,303	6,127	160,984
Acquired in-process research and development	'	'	29,461
Operating loss	-25,121	-15,415	-476,073
Other income (loss):	'	'	'
Interest income and other, net	99	237	9,948
Loss on change in warrant valuation	-3,251	-26,906	-92,246
Realized gain on sale of available-for-sale securities	'	'	3,863
Write-down of available-for-sale securities	'	'	-17,001
Total other loss	-3,152	-26,669	-95,436
Net loss	-28,273	-42,084	-571,509
Other comprehensive income (loss):	'	'	'
Write-down of available-for-sale securities	'	'	17,001
Realized gain on sale of available-for-sale securities	'	'	-3,863
Unrealized loss on available-for-sale securities	-59	'	-13,197
Total other comprehensive loss	-59	'	-59
Comprehensive loss	($28,332)	($42,084)	($571,568)
Net loss per share:	'	'	'
Net loss per share - basic and diluted	($0.75)	($1.32)	'
Weighted average number of common shares outstanding for computing basic and diluted net loss per share	37,821	31,813	'

Condensed_Consolidated_Stateme1

Condensed Consolidated Statements of Cash Flows (USD $)	3 Months Ended		404 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014
Cash flows from operating activities:	'	'	'
Net loss	($28,273)	($42,084)	($571,509)
Adjustments to reconcile net loss to net cash flows used in operating activities:	'	'	'
Depreciation and amortization	523	451	23,770
Amortization of premium on available-for-sale securities	519	'	519
Loss on abandonment of patents and disposal of property and equipment	6	196	3,232
Realized gain on sale of available-for-sale securities	'	'	-3,863
Write-down of available-for-sale securities	'	'	17,001
Impairment charge on real estate owned	'	'	1,445
Stock-based compensation	4,342	1,671	47,542
Acquired in-process research and development	'	'	29,461
Increase in warrant valuation	3,251	26,906	92,246
Net increase in accounts receivable and other assets	-10,337	-1,178	-16,297
Net increase (decrease) in accounts payable, accrued expenses and other liabilities	1,704	-955	23,585
Net cash used in operating activities	-28,265	-14,993	-352,868
Cash flows from investing activities:	'	'	'
Purchase of restricted investments	'	-7,250	-7,897
Purchase of property and equipment	-5,326	-9	-27,683
Patent costs	-294	-461	-12,228
Purchase of available-for-sale securities	-176,669	'	-289,662
Sale of available-for-sale securities	'	'	117,724
Acquisition costs	'	'	-2,389
Net cash used in investing activities	-182,289	-7,720	-222,135
Cash flows from financing activities:	'	'	'
Proceeds from exercise of options and warrants, and the sale of common stock, warrants, and partnership units, net of offering costs	2,713	2,993	625,258
Repayments of long-term debt	-23	-22	-542
Other financing activities, net	'	'	-612
Net cash provided by financing activities	2,690	2,971	624,104
Increase (decrease) in cash and cash equivalents	-207,864	-19,742	49,101
Cash and cash equivalents:	'	'	'
Beginning of period	256,965	187,661	'
End of period	49,101	167,919	49,101
Supplemental Disclosure of Cash Flow Information	'	'	'
Cash paid during the period for interest	20	22	739
Supplemental Schedule of Noncash Investing Activities and Financing Activities:	'	'	'
Available-for-sale securities received in connection with the private offering	'	'	17,897
Issuance of common stock in satisfaction of warrants and other liabilities	3,044	1,022	114,092
Tenant improvements paid by landlord	593	'	6,807
Property and equipment included in accounts payable and other liabilities	3,533	'	3,533
Building	'	'	'
Supplemental Schedule of Noncash Investing Activities and Financing Activities:	'	'	'
Issuance of common stock	'	'	750
Assumption of long-term debt	'	'	2,200
Other Assets	'	'	'
Supplemental Schedule of Noncash Investing Activities and Financing Activities:	'	'	'
Issuance of common stock	'	'	8,075
Assumption of long-term debt	'	'	$2,124

BUSINESS_AND_BASIS_OF_PRESENTA

BUSINESS AND BASIS OF PRESENTATION	3 Months Ended
	Mar. 31, 2014
Accounting Policies [Abstract]	'
BUSINESS AND BASIS OF PRESENTATION	'
	1. BUSINESS AND BASIS OF PRESENTATION
	Business
	Sarepta Therapeutics, Inc. and its wholly-owned subsidiaries (“Sarepta” or the “Company”) is a biopharmaceutical company focused on the discovery and development of unique RNA-based therapeutics for the treatment of rare and infectious diseases. Applying its proprietary platform technologies, the Company is able to target a broad range of diseases and disorders through distinct RNA-based mechanisms of action. The Company is focused on advancing the development of its Duchenne muscular dystrophy (“DMD”) drug candidates, including its lead product candidate, eteplirsen, for which the Company is currently conducting an ongoing open label extension study following completion of its initial Phase IIb clinical trials. The Company is also focused on developing therapeutics for the treatment of infectious diseases, including its lead infectious disease program aimed at the development of a drug candidate for the Marburg hemorrhagic fever virus for which the Company has historically received significant financial support from U.S. government research contracts.
	Since its inception in 1980, the Company has incurred losses of approximately $571.5 million, substantially all of which resulted from expenditures related to research and development and general and administrative charges and loss on change in warrant valuation partially offset by revenue generated from government research contracts and other grants. The Company has not generated any material revenue from product sales to date and there can be no assurance that revenue from product sales will be achieved. Moreover, even if the Company does achieve revenue from product sales, it is likely to continue to incur operating losses in the near term.
	As of March 31, 2014, the Company had $233.1 million of cash, cash equivalents and investments, consisting of $49.1 million of cash and cash equivalents, $176.1 million of short-term investments and $7.9 million of restricted investments. On April 29, 2014, the Company sold 2,650,000 shares of common stock in a public offering at a price of $38.00 per share resulting in net proceeds (after deducting underwriting discounts, commissions and other estimated offering expenses) to the Company of approximately $94.5 million. The Company believes, taking into consideration outstanding warrants and the net proceeds of $94.5 million from the common stock offering, that its balance of cash, cash equivalents and investments is sufficient to fund its current operational plan for the next twelve months. Should the Company’s funding from the U.S. government cease or be delayed, the Company would likely curtail certain of its infectious disease research and development efforts unless additional funding was obtained. The Company is also likely to pursue additional cash resources through public or private financings, seek additional government contracts and establish collaborations with or license its technology to other companies.
	Basis of Presentation
	The accompanying unaudited condensed consolidated financial statements, which have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”), reflect the accounts of Sarepta Therapeutics, Inc. and its wholly-owned subsidiaries. All inter-company transactions between and among its consolidated subsidiaries have been eliminated. Management has determined that the Company operates in one segment: the development of pharmaceutical products on its own behalf or in collaboration with others. The information included in this quarterly report on Form 10-Q should be read in conjunction with the Company’s consolidated financial statements and the accompanying notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2013.
	Estimates and Uncertainties
	The preparation of the unaudited condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, equity, revenue, expenses and the disclosure of contingent assets and liabilities. Actual results could differ from those estimates. Significant items subject to such estimates and assumptions include the valuation of stock-based awards and liability classified warrants, research and development expenses and revenue recognition.
	Reclassification
	The Company has revised the presentation as well as the caption of certain current liabilities within the unaudited condensed consolidated balance sheets to conform to the current period presentation. “Accrued liabilities” of $9.6 million as of March 31, 2013, which is broken out from “accounts payable”, and “accrued employee compensation” of $5.0 million are presented as “accrued expenses” in the unaudited condensed consolidated balance sheets. This revision had no impact on total current liabilities or total liabilities.

RECENT_ACCOUNTING_PRONOUNCEMEN

RECENT ACCOUNTING PRONOUNCEMENTS	3 Months Ended
	Mar. 31, 2014
Accounting Changes And Error Corrections [Abstract]	'
RECENT ACCOUNTING PRONOUNCEMENTS	'
	2. RECENT ACCOUNTING PRONOUNCEMENTS
	In July 2013, the Financial Accounting Standards Board (“FASB”) issued new guidance which amends the guidance related to the presentation of unrecognized tax benefits and allows for the reduction of a deferred tax asset for a net operating loss (“NOL”) carryforward whenever the NOL or tax credit carryforward would be available to reduce the additional taxable income or tax due if the tax position is disallowed. The new guidance is effective for annual and interim periods for fiscal years beginning after December 15, 2013, and early adoption is permitted. Since the guidance relates only to the presentation of unrecognized tax benefits, the adoption of this guidance did not have a material effect on the Company’s financial position, results of operations or cash flows.

ACCOUNTS_RECEIVABLE

ACCOUNTS RECEIVABLE	3 Months Ended
	Mar. 31, 2014
Text Block [Abstract]	'
ACCOUNTS RECEIVABLE	'
	3. ACCOUNTS RECEIVABLE
	The Company’s accounts receivable primarily arise from government research contracts and other grants. They are generally stated at invoiced amount and do not bear interest. Because the accounts receivable are primarily from government agencies and historically no amounts have been written off, an allowance for doubtful accounts receivable is not considered necessary. The accounts receivable balance included unbilled receivables of $5.5 million and $2.4 million at March 31, 2014 and December 31, 2013, respectively. Approximately $3.8 million of the unbilled receivables as of March 31, 2014 are subject to a U.S. government audit and will not be collected until the completion of the audit.

FAIR_VALUE_MEASUREMENTS

FAIR VALUE MEASUREMENTS	3 Months Ended
	Mar. 31, 2014
Fair Value Disclosures [Abstract]	'
FAIR VALUE MEASUREMENTS	'
	4. FAIR VALUE MEASUREMENTS
	The Company has certain financial assets and liabilities that are recorded at fair value which have been classified as Level 1, 2 or 3 within the fair value hierarchy as described in the accounting standards for fair value measurements.
		•		Level 1 — quoted prices for identical instruments in active markets;
		•		Level 2 — quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-derived valuations in which all significant inputs and significant value drivers are observable in active markets; and
		•		Level 3 — valuations derived from valuation techniques in which one or more significant value drivers are unobservable.
	The tables below present information about the Company’s financial assets and liabilities that are measured and carried at fair value and indicate the level within the fair value hierarchy of the valuation techniques it utilizes to determine such fair value:
			Fair Value Measurement as of March 31, 2014
			Total		Level 1		Level 2		Level 3
			(in thousands)
	Cash equivalents		$	8,162	$	912	$	7,250	$	—
	Commercial paper			24,890		—		24,890
	Government and government agency bonds			88,745		—		88,745		—
	Corporate bonds			62,456		—		62,456		—
	Certificates of deposit			7,897		7,897		—		—
	Total assets		$	192,150	$	8,809	$	183,341	$	—
			Fair Value Measurement as of December 31, 2013
			Total		Level 1		Level 2		Level 3
			(in thousands)
	Cash equivalents		$	185,000	$	185,000	$	—	$	—
	Certificates of deposit			7,897		7,897		—		—
	Total assets		$	192,897	$	192,897	$	—	$	—
			Fair Value Measurement as of March 31, 2014
			Total		Level 1		Level 2		Level 3
			(in thousands)
	Warrants		$	9,213	$	—	$	—	$	9,213
	Total liabilities		$	9,213	$	—	$	—	$	9,213
			Fair Value Measurement as of December 31, 2013
			Total		Level 1		Level 2		Level 3
			(in thousands)
	Warrants		$	9,006	$	—	$	—	$	9,006
	Total liabilities		$	9,006	$	—	$	—	$	9,006
	The cash equivalents include money market funds, commercial paper and government and government agency bonds. Money market funds are publicly traded mutual funds and, thus, the fair value of these assets is categorized as Level 1 within the fair value hierarchy.
	The majority of the Company’s financial assets, consisting of commercial paper, government and government agency bonds and corporate bonds, have been initially valued at the transaction price and subsequently valued, at the end of each reporting period, through income-based approaches utilizing market observable data. Thus, the fair value of these assets is categorized as Level 2 within the fair value hierarchy.
	The warrants issued in January and August 2009 are classified as liabilities. The fair value is determined using the Black-Scholes-Merton option-pricing model, which requires the use of significant judgment and estimates for the inputs in the model. Accordingly, the fair value of these liabilities is categorized as Level 3 within the fair value hierarchy. For additional information related to the determination of fair value of warrants and a reconciliation of changes in fair value, please read Note 7, Warrants of the unaudited condensed consolidated financial statements.
	The carrying amounts reported in the unaudited condensed consolidated balance sheets for cash, accounts receivable and accounts payable approximate fair value because of the immediate or short-term maturity of these financial instruments and carrying amounts reported for long-term debt approximate fair value based on market activity for other debt instruments with similar characteristics and comparable risk.

CASH_CASH_EQUIVALENTS_AND_SHOR

CASH, CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS	3 Months Ended
	Mar. 31, 2014
Cash And Cash Equivalents [Abstract]	'
CASH, CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS	'
	5. CASH, CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS
	It is the Company’s policy to mitigate credit risk in its financial assets by maintaining a well-diversified portfolio that limits the amount of exposure as to maturity and investment type. The following tables summarize the Company’s cash, cash equivalents and short-term investments for each of the periods indicated:
		As of March 31, 2014
		Amortized		Gross		Gross			Fair
		Cost		Unrealized		Unrealized			Market
				Gains		Losses			Value
		(in thousands)
	Cash, money market funds, commercial paper and government and government agency bonds	$	49,101	$	—	$	—		$	49,101
	Commercial paper		24,892		1		(3	)		24,890
	Government and government agency bonds		88,755		4		(14	)		88,745
	Corporate bonds		62,503		—		(47	)		62,456
	Total	$	225,251	$	5	$	(64	)	$	225,192
	As reported:
	Cash and cash equivalents		49,101		—		—			49,101
	Short-term investments		176,150		5		(64	)		176,091
	Total	$	225,251	$	5	$	(64	)	$	225,192
		As of December 31, 2013
		Amortized		Gross		Gross			Fair
		Cost		Unrealized		Unrealized			Market
				Gains		Losses			Value
		(in thousands)
	Cash and money market funds	$	256,965	$	—	$	—		$	256,965
	Total	$	256,965	$	—	$	—		$	256,965
	As reported:
	Cash and cash equivalents	$	256,965	$	—	$	—		$	256,965
	Total	$	256,965	$	—	$	—		$	256,965

PROPERTY_AND_EQUIPMENT

PROPERTY AND EQUIPMENT	3 Months Ended
	Mar. 31, 2014
Property Plant And Equipment [Abstract]	'
PROPERTY AND EQUIPMENT	'
	6. PROPERTY AND EQUIPMENT
	Property and equipment are recorded at historical cost, net of accumulated depreciation. They are subject to impairment analysis whenever events or changes in circumstances indicate that the carrying amount of the assets may not be recoverable. The cost of normal, recurring or periodic repairs and maintenance activities related to property and equipment is expensed as incurred. The cost for planned major maintenance activities, including the related acquisition or construction of assets, is capitalized if the project will result in future economic benefits.
	The following table summarizes the Company’s property and equipment for each of the periods indicated:
		As of			As of
		March 31,			December 31,
		2014			2013
		(in thousands)
	Lab equipment	$	8,332		$	7,728
	Office equipment		2,210			306
	Software and computer equipment		2,955			1,126
	Building		1,856			1,856
	Leasehold improvements		21,359			10,058
	Construction in progress		521			11,303
	Property and equipment, gross		37,233			32,377
	Less: accumulated depreciation		(17,103	)		(17,328	)
	Property and equipment, net	$	20,130		$	15,049
	At December 31, 2013, the Company recorded construction in progress related to the Cambridge headquarter lease totaling $11.3 million, of which $6.2 million was paid by the landlord as part of a tenant improvement allowance which was recorded in other long-term liabilities. These assets were placed into service, reclassified to their respective asset category and depreciation commenced during the first quarter of 2014.
	Depreciation expense was $0.4 million and $0.3 million for the three months ended March 31, 2014 and 2013, respectively.

WARRANTS

WARRANTS	3 Months Ended
	Mar. 31, 2014
Derivative Instruments And Hedging Activities Disclosure [Abstract]	'
WARRANTS	'
	7. WARRANTS
	The Company has periodically issued warrants in connection with certain common stock offerings. The warrants issued in January and August 2009 are classified as liabilities as opposed to equity due to their settlement terms which require settlement in registered shares. These warrants are non-cash liabilities and the Company is not required to expend any cash to settle these liabilities.
	The outstanding warrants classified as liabilities are recorded on the unaudited condensed consolidated balance sheets and are adjusted to fair value at each financial reporting period, with changes in the fair value being recorded as “Gain (loss) on change in warrant valuation” in the unaudited condensed consolidated statements of operations and comprehensive loss. Fair value is determined using the Black-Scholes-Merton option-pricing model, which requires the use of significant judgment and estimates for the inputs used in the model.
	The following table reflects the weighted-average assumptions for each of the periods indicated:
			For the Three Months Ended March 31,
			2014			2013
	Risk-free interest rate (1)			0.10%			0.10%
	Expected dividend yield (2)			0%			0%
	Expected lives (3)			0.3-0.4 year			0.8-1.4 years
	Expected volatility (4)			101.81%-121.88%			99.4%-110.7%
	Shares underlying warrants classified as liabilities			633,740			3,093,676
	Market value of stock at beginning of the period		$	20.37		$	25.8
	Market value of stock at end of the period		$	24.03		$	36.95
	-1	The risk-free interest rate is estimated using an average of U.S. Treasury bill interest rates that correlate to the prevailing interest rates at the valuation date.
	-2	The expected dividend yield is zero as the Company has not paid any dividends to date and does not expect to pay dividends prior to the expiration of the warrants.
	-3	The expected lives are based on the remaining contractual lives of the related warrants at the valuation date.
	-4	The expected volatility is estimated using a blend of calculated volatility of the Company’s common stock over a historical period and implied volatility in exchange-traded options associated with the Company’s common stock.
	The amounts estimated according to the Black-Scholes-Merton option-pricing model may not be indicative of the actual values realized upon the exercise of these warrants by the holders.
	The following table summarizes the reconciliation of the change in value of the Company’s liability classified warrants for each of the periods indicated:
			For the Three Months Ended March 31,
			2014			2013
			(in thousands)
	Balance at beginning of the period		$	9,006		$	65,193
	Increase in value of warrants			3,251			26,906
	Reclassification to stockholders’ equity upon exercise of warrants			(3,044	)		(1,022	)
	Balance at end of the period		$	9,213		$	91,077
	The following table summarizes the Company’s warrant activity for each of the periods indicated:
			For the Three Months Ended March 31,
			2014						2013
			Shares			Weighted			Shares			Weighted
						Average						Average
						Exercise						Exercise
						Price						Price
	Warrants outstanding at beginning of the period			791,508		$	10.5			3,127,618		$	8.48
	Exercised			(157,768	)		10.59			(33,942	)		8.16
	Warrants outstanding at end of the period			633,740		$	9.92			3,093,676		$	8.49
	Warrants exercisable at end of the period			633,740			9.92			3,093,676			8.49
	The following table summarizes the Company’s warrants outstanding at March 31, 2014:
	Issue Date		Exercise			Outstanding			Expiration
			Price			Warrants			Date
	1/30/09		$	6.96			129,768			7/30/14
	8/25/09		$	10.68			503,972			8/31/14

ACCRUED_EXPENSES

ACCRUED EXPENSES	3 Months Ended
	Mar. 31, 2014
Payables And Accruals [Abstract]	'
ACCRUED EXPENSES	'
	8. ACCRUED EXPENSES
	The following table summarizes the Company’s accrued expenses for each of the periods indicated:
		As of		As of
		March 31,		December 31,
		2014		2013
		(in thousands)
	Accrued contract manufacturing costs	$	5,169	$	1,414
	Accrued facility-related costs		3,531		2,843
	Accrued contract research costs		2,623		2,785
	Accrued employee compensation costs		2,611		5,048
	Accrued professional fees		1,606		1,235
	Others		800		1,276
	Total accrued expenses	$	16,340	$	14,601

GOVERNMENT_CONTRACTS

GOVERNMENT CONTRACTS	3 Months Ended
	Mar. 31, 2014
Contractors [Abstract]	'
GOVERNMENT CONTRACTS	'
	9. GOVERNMENT CONTRACTS
	The Company recognizes revenue from U.S. and European Union (E.U.) government research contracts during the period in which the related expenditures are incurred and presents revenue and related expenses gross in the unaudited condensed consolidated statements of operations and comprehensive loss. In the periods presented, substantially all of the revenue generated by the Company was derived from government research contracts.
	The following table summarizes the revenue for each of our contracts with the U.S. and E.U. governments for each of the periods indicated:
		For the Three Months Ended
		March 31,
		2014		2013
		(in thousands)
	July 2010 Contract (Ebola and Marburg IV)	$	4,064	$	2,614
	August 2012 Contract (Intramuscular)		—		1,806
	November 2012 SKIP-NMD Agreement (DMD)		1,365		54
	July 2013 Children’s National Medical Center (DMD)		659		—
	Total	$	6,088	$	4,474
	July 2010 Contract (Ebola and Marburg Intravenous administration)
	In July 2010, the Company was awarded the Department of Defense (“DoD”) contract managed by its Joint Project Manager Medical Countermeasure Systems (“JPM-MCS”) program for the advanced development of its hemorrhagic fever virus therapeutic candidates, AVI-6002 and AVI-6003, against the Ebola and Marburg viruses, respectively. In February 2012, the Company announced that it received permission from the U.S. Food and Drug Administration (“FDA”) to proceed with a single oligomer from AVI-7288, one of the two components that make up AVI-6003, as the lead product candidate against Marburg virus infection. In August 2012, the Company received a stop-work order related to the Ebola virus portion of the contract and, in October 2012, the DoD terminated the Ebola portion of the contract for the convenience of the government due to government funding constraints.
	The remaining Marburg portion of the contract is structured into four segments and has an aggregate remaining period of performance spanning approximately four years if DoD exercises its options for all segments. Activities under the first segment began in July 2010 and include preclinical studies and Phase I studies in healthy volunteers. In February 2014, the Company announced positive safety results from the Phase I multiple ascending dose study of AVI-7288.
	After completion of the first segment, DoD has the option to proceed to the next segment. If DoD exercises its options for segments II, III and IV, the Company’s contract activities would include all clinical and licensure activities necessary to obtain FDA regulatory approval for the therapeutic candidate against the Marburg virus. The funding for segments II, III and IV of the Marburg virus portion of the contract is estimated to be approximately $84.4 million.
	During the three months ended March 31, 2014 and 2013, the Company recognized $4.1 million and $2.6 million as revenue under this agreement, respectively.
	August 2012 Agreement (Intramuscular)
	In August 2012, the Company was awarded a contract from the JPM-MCS program. The contract was for approximately $3.9 million to evaluate the feasibility of an intramuscular route of administration using AVI-7288, the Company’s candidate for treatment of Marburg virus. The period of performance for this contract concluded in the third quarter of 2013. No revenue was recognized under this agreement for the three months ended March 31, 2014. The Company recognized $1.8 million as revenue under this agreement for the three months ended March 31, 2013.
	European Union SKIP-NMD Agreement (DMD)
	In November 2012, the Company entered into an agreement for a collaborative research project partially funded by the E.U. Health Innovation. The agreement provides for approximately $2.5 million for research in certain development and study related activities for a DMD therapeutic and is expected to last approximately three years. During the three months ended March 31, 2014 and 2013, the Company recognized $1.4 million and less than $0.1 million as revenue under this agreement, respectively. Revenue under this agreement has been fully recognized as March 31, 2014.
	July 2013 Children’s National Medical Center (“CNMC”) Agreement (DMD)
	In July 2013, the Company entered into an agreement totaling $1.3 million to provide a drug product to CNMC to conduct research related to the Company’s DMD program. During the three months ended March 31, 2014, the Company recognized $ 0.7 million as revenue under the agreement. Revenue under this agreement has been fully recognized as March 31, 2014.

STOCKBASED_COMPENSATION

STOCK-BASED COMPENSATION	3 Months Ended
	Mar. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'
STOCK-BASED COMPENSATION	'
	10. STOCK-BASED COMPENSATION
	The Company’s equity incentive plans allow for the granting of a variety of stock awards. To date, the Company has granted stock options, restricted stock awards, restricted stock units and stock appreciation rights. The fair value of stock awards, with consideration given to estimated forfeitures, is recognized as compensation expense on a straight-line basis over the vesting period of the grants.
	Stock Options
	The Company has granted stock options with both service- and performance-based criteria. In general, stock options granted vest over four years and have a ten-year term. As of March 31, 2014, the achievement of the performance criteria is not probable and, accordingly, the Company has not recognized any expense related to the options with performance-based criteria.
	The following table summarizes the Company’s stock option activity for each of the periods indicated:
			For the Three Months Ended March 31,
			2014						2013
			Shares			Weighted			Shares			Weighted
						Average						Average
						Exercise						Exercise
						Price						Price
	Grants outstanding at beginning of the period			4,190,367		$	23.46			2,522,522		$	11.76
	Granted			1,185,265			26.83			242,320			28.76
	Exercised			(48,579	)		10.39			(64,390	)		8.97
	Canceled or expired			(53,715	)		30.26			(5,774	)		14.83
	Grants outstanding at end of the period			5,273,338		$	24.27			2,694,678		$	13.35
	Grants exercisable at end of the period			1,180,245		$	12.85			656,805		$	12.36
	The fair values of stock options granted during the periods presented were measured on the date of grant using the Black-Scholes-Merton option-pricing model, with the following assumptions:
			For the Three Months Ended March 31,
			2014			2013
	Risk-free interest rate (1)			1.7	%		0.7	%
	Expected dividend yield (2)			0	%		0	%
	Expected lives (3)			4.9 years			4.9 years
	Expected volatility (4)			95.4	%		80	%
	-1	The risk-free interest rate is estimated using an average of Treasury bill interest rates over a historical period commensurate with the expected term of the option that correlates to the prevailing interest rates at the time of grant.
	-2	The expected dividend yield is zero as the Company has not paid any dividends to date and does not expect to pay dividends in the future.
	-3	The expected lives are estimated using expected and historical exercise behavior.
	-4	The expected volatility is estimated using a blend of calculated volatility of the Company’s common stock over a historical period and implied volatility in exchange-traded options of the Company’s common stock.
	The amounts estimated according to the Black-Scholes-Merton option-pricing model may not be indicative of the actual values realized upon the exercise of these options by the holders.
	Restricted Stock Awards (“RSA”)
	The Company grants RSAs to members of its board of directors. The weighted-average grant date fair value of RSAs is based on the market price of the Company’s common stock on the date of grant. The fair value is amortized to stock-based compensation expense on a straight-line basis over the vesting period of the grants. The following table summarizes the Company’s RSA activity for each of the periods indicated:
			For the Three Months Ended March 31,
			2014						2013
			Shares			Weighted			Shares			Weighted
						Average						Average
						Grant Date						Grant Date
						Fair Value						Fair Value
	Grants outstanding at beginning of the period			6,000		$	34.92			4,998		$	10.08
	Granted			6,000			29.03			—			—
	Grants outstanding at end of the period			12,000		$	31.98			4,998		$	10.08
	Restricted Stock Units (“RSU”)
	The Company granted RSUs to employees in 2012. The weighted-average grant date fair value of RSUs is based on the market price of the Company’s common stock on the date of grant. The fair value is amortized to stock-based compensation expense on a straight-line basis over the vesting period of the grants. The following table summarizes the Company’s RSU activity for each of the periods indicated:
			For the Three Months Ended March 31,
			2014						2013
			Shares			Weighted			Shares			Weighted
						Average						Average
						Grant Date						Grant Date
						Fair Value						Fair Value
	Grants outstanding at beginning of the period			6,507		$	5.4			38,260		$	6.32
	Canceled or expired			—			—			(262	)		5.4
	Grants outstanding at end of the period			6,507		$	5.4			37,998		$	6.33
	Stock Appreciation Rights (“SAR”)
	The Company issues SARs to employees on the same terms as the stock options granted to employees. The grant date fair value of the SARs is determined using the same valuation assumptions as for the stock options described above. Stock-based compensation expense is recognized on a straight-line basis over the vesting period of the SARs. The following table summarizes the Company’s SAR activity for each of the periods indicated:
			For the Three Months Ended March 31,
			2014						2013
			Shares			Weighted			Shares			Weighted
						Average						Average
						Exercise						Exercise
						Price						Price
	Grants outstanding at beginning of the period			170,000		$	18.18			170,000		$	18.18
	Grants outstanding at end of the period			170,000		$	18.18			170,000		$	18.18
	Grants exercisable at end of the period			61,041		$	17.6			—		$	—
	Employee Stock Purchase Plan (“ESPP”)
Under the Company’s ESPP, participating employees purchase common stock through payroll deductions. The purchase price is equal to 85% of the lower of the closing price of the Company’s common stock on the first business day and the last business day of the relevant plan period. The 24-month award period will end on February 29, 2016. For the purchasing period ended February 28, 2014, 21,774 shares of the Company’s common stock were purchased for total proceeds of $0.5 million.
The fair values of stock purchase rights were estimated using the Black-Scholes-Merton option-pricing model. The following table summarizes the assumptions used in the calculation during the period indicated:
		For the Three
		Months Ended
		March 31, 2014
Fair value of stock purchase rights		$12.22 - 25.35
Weighted-average stock price volatility		101% - 109%
Expected lives		0.5 - 2 years
Risk-free rate		0.1% - 0.3%
Stock-based Compensation Expense
For the three months ended March 31, 2014 and 2013, total stock-based compensation expense was $4.3 million and $1.7 million, respectively. The following table summarizes share-based compensation expense by function included within the unaudited condensed consolidated statements of operations and comprehensive loss:
		For the Three Months Ended March 31,
		2014			2013
Research and development		$	1,873		$	530
General and administrative			2,469			1,141
Total		$	4,342		$	1,671
The following table summarizes share-based compensation expense by grant type included within the unaudited condensed consolidated statements of operations and comprehensive loss:
		For the Three Months Ended March 31,
		2014			2013
Stock options		$	3,911		$	1,401
Restricted stock awards			64			12
Restricted stock units			(4	)		117
Stock appreciation rights			147			141
Employee stock purchase plan			224			—
Total		$	4,342		$	1,671

NET_LOSS_PER_SHARE

NET LOSS PER SHARE	3 Months Ended
	Mar. 31, 2014
Earnings Per Share [Abstract]	'
NET LOSS PER SHARE	'
	11. NET LOSS PER SHARE
	Basic net loss per share is computed by dividing net loss by the weighted-average number of shares of common stock outstanding. Diluted net loss per share is computed by dividing net loss by the weighted-average number of shares of common stock and dilutive common stock equivalents outstanding. Given that the Company is in a loss position for each of the periods presented, there is no difference between basic and diluted net loss per share since the effect of common stock equivalents would be anti-dilutive and are, therefore, excluded from the diluted net loss per share calculation.
			For the Three Months Ended March 31,
			2014			2013
			(in thousands, except per share amounts)
	Net loss		$	(28,273	)	$	(42,084	)
	Weighted-average number of shares of common stock and common stock equivalents outstanding:
	Weighted-average number of shares of common stock outstanding for computing basic earnings per share			37,821			31,813
	Dilutive effect of outstanding warrants and stock options after application of the treasury stock method*			—			—
	Weighted-average number of shares of common stock and dilutive common stock equivalents outstanding for computing diluted earnings per share			37,821			31,813
	Net loss per share — basic and diluted		$	(0.75	)	$	(1.32	)
	*	Warrants, stock options, restricted stock awards, restricted stock units and stock appreciation rights to purchase approximately 6,096,000 and 5,997,000 shares of common stock were excluded from the net loss per share calculation for the three months ended March 31, 2014 and 2013, respectively, as their effect would have been anti-dilutive.

INCOME_TAXES

INCOME TAXES	3 Months Ended
	Mar. 31, 2014
Income Tax Disclosure [Abstract]	'
INCOME TAXES	'
	12. INCOME TAXES
	As of December 31, 2013, the Company had gross deferred tax assets of $133.6 million primarily from U.S. federal and state NOL carryforwards, U.S. federal and state research and development credit carryforwards, stock-based compensation expense and intangibles. Due to uncertainties surrounding the Company’s ability to generate future taxable income to realize these assets, a full valuation allowance has been established to offset its net deferred tax asset. Additionally, the Internal Revenue Code rules could limit the future use of its NOL and research and development credit carryforwards to offset future taxable income based on ownership changes and the value of the Company’s common stock.

RESTRUCTURING

RESTRUCTURING	3 Months Ended
	Mar. 31, 2014
Restructuring And Related Activities [Abstract]	'
RESTRUCTURING	'
	13. RESTRUCTURING
	In November 2012, the Company notified 21 Bothell, Washington based employees that they would be terminated as part of the corporate headquarters relocation to Cambridge, Massachusetts. The employees were given various incentives to remain through a transition period which was completed in 2013. During the first quarter of 2014, the transition period was extended to the end of the second quarter of 2014 for one employee. For the three months ended March 31, 2014, the Company recorded a restructuring charge of less than $0.1 million to research and development expenses. For the three months ended March 31, 2013, the Company recorded a restructuring charge of $0.3 million to research and development expenses and $0.2 million to general and administrative expenses.
	Changes in the liability and the balance related to the restructuring plan are as follows:
		For the Three Months Ended March 31,
		2014			2013
		(in thousands)
	Balance at beginning of the period	$	44		$	185
	Restructuring charges		9			462
	Payments		(8	)		(201	)
	Balance at end of the period	$	45		$	446

COMMITMENTS_AND_CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	3 Months Ended
	Mar. 31, 2014
Commitments And Contingencies Disclosure [Abstract]	'
COMMITMENTS AND CONTINGENCIES	'
	14. COMMITMENTS AND CONTINGENCIES
	Lease Obligations
	In June 2013, the Company entered into a lease agreement for its headquarters located in Cambridge, Massachusetts. The agreement calls for a security deposit in the form of a letter of credit totaling $0.6 million. The Company purchased a certificate of deposit (“CD”) to meet the requirement and it was recorded as a long-term restricted investment in the unaudited condensed consolidated balance sheets as of March 31, 2014. The initial term of the lease agreement is for seven years with an average annual base rent of approximately $2.4 million.
	In November 2013, the Company entered into the first amendment of its lease agreement for its headquarters located in Cambridge, Massachusetts. The amendment modified the original lease to add an additional 15,077 square feet to its original space, increasing its total rental space for its headquarters to 61,453 square feet. The amendment calls for additional annual base rent of approximately $0.5 million, subject to a 2.5% annual increase. In January 2014, the Company entered into a sublease for the 15,077 square feet of office space with an unrelated third party for an 18-month term with a total base rent of approximately $0.7 million.
	The Company also leases laboratory and office space in Corvallis, Oregon. The annual base rent at the Corvallis, Oregon facility is approximately $0.9 million, excluding other occupancy costs, and is subject to an annual increase of 3%.
	For the three months ended March 31, 2014 and 2013, rent expense and occupancy costs under all leases totaled $1.1 million and $0.6 million, respectively. The aggregate non-cancelable future minimum payments under leases were as follows:
		As of
		March 31, 2014
		(in thousands)
	2014 (9 months)	$	2,790
	2015		3,807
	2016		3,895
	2017		3,986
	2018		4,079
	Thereafter		8,889
	Total minimum lease payments	$	27,446
	Royalty Obligations
	The Company has license agreements for which it is obligated to pay minimum royalties if the Company does not terminate the relevant agreement. The notice period to terminate these agreements is six months or less. Royalty payments under these agreements were less than $0.1 million for the three months ended March 31, 2014 and 2013, respectively.
	The Company is also obligated to pay royalties upon the net sales of DMD products. The royalty rates are in the low single-digit percentages for both inside and outside the United States. Under the agreement with Charley’s Fund, Inc. signed in October 2007, the Company is obligated to pay a mid single-digit percentage royalty on the net sales of any product developed pursuant to the agreement with Charley’s Fund up to a maximum of $3.4 million. In May 2003, the Company entered into a collaboration and license agreement with Isis-Ercole. The range of percentage of royalty payments under this agreement, should such payments ever be made, is from a fraction of a percent to mid-single-digit percentages.
	Milestone Obligations
	The Company has license agreements for which it is obligated to pay development milestones as a product candidate proceeds from the filing of an Investigational New Drug application through approval for commercial sale. There were no milestone payments under these agreements for the three months ended March 31, 2014 and 2013, respectively.
	Under the collaboration and license agreement with Isis-Ercole, the Company may be obligated to make up to $23.4 million milestone payments. As of March 31, 2014, the Company has not made any payments under this agreement and is not under any current obligation to make any such milestone payments, as the conditions triggering any such milestone payment obligations have not been satisfied. Subject to the satisfaction of certain milestones triggering the obligation to make any such payments, Isis may be obligated to make milestone payments to the Company of up to $21.1 million in the aggregate for each product developed under a licensed patent under this agreement. As of March 31, 2014, Isis has not made and is not under any current obligation to make any such milestone payments, as the conditions triggering any such milestone payment obligations have not been satisfied.
	In April 2013, the Company and the University of Western Australia (“UWA”) entered into an agreement under which an existing exclusive license agreement between the Company and UWA was amended and restated. Under the terms of this agreement, UWA granted the Company an exclusive license to certain UWA intellectual property rights in exchange for up to $7.1 million in upfront and development milestone payments.
	In March 2014, the Company entered into a patent assignment agreement with a group of scientists (collectively, “Assignors”). Under the terms of the agreement, the Assignors will transfer to the Company all rights, title and interest in certain patent rights as well as technical information related to the patents. The Company may be obligated to make up to $2.7 million in development and commercial milestone payments. As of March 31, 2014, the Company made an up-front payment of $0.3 million under this agreement, which was recorded as research and development expense.
	Litigation
	In the normal course of business, the Company may from time to time be named as a party to various legal claims, actions and complaints, including matters involving securities, employment, intellectual property, effects from the use of therapeutics utilizing its technology, or others. For example, in January 2014, a former consultant of the Company filed a complaint alleging breach of contract, among other claims, and seeking approximately $4 million in damages, plus certain additional fees and costs, from the Company. In addition, purported class action complaints were filed against the Company and certain of its officers in the U.S. District Court for the District of Massachusetts on January 27, 2014 (Corban v. Sarepta et al) and January 29, 2014 (Baradanian v. Sarepta et al). The plaintiffs are alleged purchasers of Company common stock who seek to bring claims on behalf of themselves and persons or entities that purchased or acquired securities of the Company between July 24, 2013 and November 12, 2013. The complaints allege that the defendants violated the federal securities laws in connection with disclosures related to eteplirsen, the Company’s lead therapeutic candidate for DMD, and seek damages in an unspecified amount. Given the relatively early stages of the proceedings in the above mentioned purported claims, at this time, no assessment can be made as to the likely outcome of these claims or whether the outcomes would have a material impact on the Company.
	Purchase Commitments
	In the Company’s continuing operations, it has entered into long-term contractual arrangements from time to time for the provision of goods and services. The following table presents non-cancelable contractual obligations arising from these arrangements:
		As of
		March 31, 2014
		(in thousands)
	2014 (9 months)	$	38,528
	2015		44,901
	2016		42,779
	2017		21,390
	2018		14,260
	Thereafter		3,565
	Total purchase commitments	$	165,423
	In February 2013, the Company issued two letters of credit totaling $7.3 million to a contract manufacturing vendor in connection with certain manufacturing agreements. The obligations secured by the letters of credit are fulfilled upon payment for certain minimum volume commitments and construction milestones. To meet the requirement of the letters of credit, the Company purchased $7.3 million in CDs with May 2014 maturity dates. If the minimum volume commitments and construction milestones have not occurred at that time, the letters of credit will be extended. The $7.3 million was recorded as restricted investments in the unaudited condensed consolidated balance sheets as of March 31, 2014.

SUBSEQUENT_EVENT

SUBSEQUENT EVENT	3 Months Ended
	Mar. 31, 2014
Subsequent Events [Abstract]	'
SUBSEQUENT EVENT	'
	15. SUBSEQUENT EVENT
	On April 29, 2014, the Company sold 2,650,000 shares of common stock at an offering price of $38.00 per share. In addition, the Company has granted the underwriters an option to purchase an additional 397,500 shares of common stock at a price of $38.00 per share. The Company received aggregate net proceeds of approximately $94.5 million, after deducting the underwriting discounts and offering related transaction costs.

BUSINESS_AND_BASIS_OF_PRESENTA1

BUSINESS AND BASIS OF PRESENTATION (Policies)	3 Months Ended
	Mar. 31, 2014
Accounting Policies [Abstract]	'
Basis of Presentation	'
	Basis of Presentation
	The accompanying unaudited condensed consolidated financial statements, which have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”), reflect the accounts of Sarepta Therapeutics, Inc. and its wholly-owned subsidiaries. All inter-company transactions between and among its consolidated subsidiaries have been eliminated. Management has determined that the Company operates in one segment: the development of pharmaceutical products on its own behalf or in collaboration with others. The information included in this quarterly report on Form 10-Q should be read in conjunction with the Company’s consolidated financial statements and the accompanying notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2013.
Estimates and Uncertainties	'
	Estimates and Uncertainties
	The preparation of the unaudited condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, equity, revenue, expenses and the disclosure of contingent assets and liabilities. Actual results could differ from those estimates. Significant items subject to such estimates and assumptions include the valuation of stock-based awards and liability classified warrants, research and development expenses and revenue recognition.
Reclassification	'
	Reclassification
	The Company has revised the presentation as well as the caption of certain current liabilities within the unaudited condensed consolidated balance sheets to conform to the current period presentation. “Accrued liabilities” of $9.6 million as of March 31, 2013, which is broken out from “accounts payable”, and “accrued employee compensation” of $5.0 million are presented as “accrued expenses” in the unaudited condensed consolidated balance sheets. This revision had no impact on total current liabilities or total liabilities.
Recent Accounting Pronouncements	'
	In July 2013, the Financial Accounting Standards Board (“FASB”) issued new guidance which amends the guidance related to the presentation of unrecognized tax benefits and allows for the reduction of a deferred tax asset for a net operating loss (“NOL”) carryforward whenever the NOL or tax credit carryforward would be available to reduce the additional taxable income or tax due if the tax position is disallowed. The new guidance is effective for annual and interim periods for fiscal years beginning after December 15, 2013, and early adoption is permitted. Since the guidance relates only to the presentation of unrecognized tax benefits, the adoption of this guidance did not have a material effect on the Company’s financial position, results of operations or cash flows.

FAIR_VALUE_MEASUREMENTS_Tables

FAIR VALUE MEASUREMENTS (Tables)	3 Months Ended
	Mar. 31, 2014
Fair Value Disclosures [Abstract]	'
Assets and Liabilities Measured and Carried at Fair Value	'
	The tables below present information about the Company’s financial assets and liabilities that are measured and carried at fair value and indicate the level within the fair value hierarchy of the valuation techniques it utilizes to determine such fair value:
		Fair Value Measurement as of March 31, 2014
		Total		Level 1		Level 2		Level 3
		(in thousands)
	Cash equivalents	$	8,162	$	912	$	7,250	$	—
	Commercial paper		24,890		—		24,890
	Government and government agency bonds		88,745		—		88,745		—
	Corporate bonds		62,456		—		62,456		—
	Certificates of deposit		7,897		7,897		—		—
	Total assets	$	192,150	$	8,809	$	183,341	$	—
		Fair Value Measurement as of December 31, 2013
		Total		Level 1		Level 2		Level 3
		(in thousands)
	Cash equivalents	$	185,000	$	185,000	$	—	$	—
	Certificates of deposit		7,897		7,897		—		—
	Total assets	$	192,897	$	192,897	$	—	$	—
		Fair Value Measurement as of March 31, 2014
		Total		Level 1		Level 2		Level 3
		(in thousands)
	Warrants	$	9,213	$	—	$	—	$	9,213
	Total liabilities	$	9,213	$	—	$	—	$	9,213
		Fair Value Measurement as of December 31, 2013
		Total		Level 1		Level 2		Level 3
		(in thousands)
	Warrants	$	9,006	$	—	$	—	$	9,006
	Total liabilities	$	9,006	$	—	$	—	$	9,006

CASH_CASH_EQUIVALENTS_AND_SHOR1

CASH, CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS (Tables)	3 Months Ended
	Mar. 31, 2014
Cash And Cash Equivalents [Abstract]	'
Summary of Company Cash , Cash Equivalents and Short-Term Investments	'
	The following tables summarize the Company’s cash, cash equivalents and short-term investments for each of the periods indicated:
		As of March 31, 2014
		Amortized		Gross		Gross			Fair
		Cost		Unrealized		Unrealized			Market
				Gains		Losses			Value
		(in thousands)
	Cash, money market funds, commercial paper and government and government agency bonds	$	49,101	$	—	$	—		$	49,101
	Commercial paper		24,892		1		(3	)		24,890
	Government and government agency bonds		88,755		4		(14	)		88,745
	Corporate bonds		62,503		—		(47	)		62,456
	Total	$	225,251	$	5	$	(64	)	$	225,192
	As reported:
	Cash and cash equivalents		49,101		—		—			49,101
	Short-term investments		176,150		5		(64	)		176,091
	Total	$	225,251	$	5	$	(64	)	$	225,192
		As of December 31, 2013
		Amortized		Gross		Gross			Fair
		Cost		Unrealized		Unrealized			Market
				Gains		Losses			Value
		(in thousands)
	Cash and money market funds	$	256,965	$	—	$	—		$	256,965
	Total	$	256,965	$	—	$	—		$	256,965
	As reported:
	Cash and cash equivalents	$	256,965	$	—	$	—		$	256,965
	Total	$	256,965	$	—	$	—		$	256,965

PROPERTY_AND_EQUIPMENT_Tables

PROPERTY AND EQUIPMENT (Tables)	3 Months Ended
	Mar. 31, 2014
Property Plant And Equipment [Abstract]	'
Summary of Company's Property and Equipment	'
	The following table summarizes the Company’s property and equipment for each of the periods indicated:
		As of			As of
		March 31,			December 31,
		2014			2013
		(in thousands)
	Lab equipment	$	8,332		$	7,728
	Office equipment		2,210			306
	Software and computer equipment		2,955			1,126
	Building		1,856			1,856
	Leasehold improvements		21,359			10,058
	Construction in progress		521			11,303
	Property and equipment, gross		37,233			32,377
	Less: accumulated depreciation		(17,103	)		(17,328	)
	Property and equipment, net	$	20,130		$	15,049

WARRANTS_Tables

WARRANTS (Tables)	3 Months Ended
	Mar. 31, 2014
Reconciliation of Change in Value of Company's Warrants Liability	'
	The following table summarizes the reconciliation of the change in value of the Company’s liability classified warrants for each of the periods indicated:
			For the Three Months Ended March 31,
			2014			2013
			(in thousands)
	Balance at beginning of the period		$	9,006		$	65,193
	Increase in value of warrants			3,251			26,906
	Reclassification to stockholders’ equity upon exercise of warrants			(3,044	)		(1,022	)
	Balance at end of the period		$	9,213		$	91,077
Summary of Warrant Activity	'
	The following table summarizes the Company’s warrant activity for each of the periods indicated:
			For the Three Months Ended March 31,
			2014						2013
			Shares			Weighted			Shares			Weighted
						Average						Average
						Exercise						Exercise
						Price						Price
	Warrants outstanding at beginning of the period			791,508		$	10.5			3,127,618		$	8.48
	Exercised			(157,768	)		10.59			(33,942	)		8.16
	Warrants outstanding at end of the period			633,740		$	9.92			3,093,676		$	8.49
	Warrants exercisable at end of the period			633,740			9.92			3,093,676			8.49
Summary of Company's Warrants Outstanding	'
	The following table summarizes the Company’s warrants outstanding at March 31, 2014:
	Issue Date		Exercise			Outstanding			Expiration
			Price			Warrants			Date
	1/30/09		$	6.96			129,768			7/30/14
	8/25/09		$	10.68			503,972			8/31/14
Warrant	'
Weighted-Average Assumptions	'
	The following table reflects the weighted-average assumptions for each of the periods indicated:
			For the Three Months Ended March 31,
			2014			2013
	Risk-free interest rate (1)			0.10%			0.10%
	Expected dividend yield (2)			0%			0%
	Expected lives (3)			0.3-0.4 year			0.8-1.4 years
	Expected volatility (4)			101.81%-121.88%			99.4%-110.7%
	Shares underlying warrants classified as liabilities			633,740			3,093,676
	Market value of stock at beginning of the period		$	20.37		$	25.8
	Market value of stock at end of the period		$	24.03		$	36.95
	-1	The risk-free interest rate is estimated using an average of U.S. Treasury bill interest rates that correlate to the prevailing interest rates at the valuation date.
	-2	The expected dividend yield is zero as the Company has not paid any dividends to date and does not expect to pay dividends prior to the expiration of the warrants.
	-3	The expected lives are based on the remaining contractual lives of the related warrants at the valuation date.
	-4	The expected volatility is estimated using a blend of calculated volatility of the Company’s common stock over a historical period and implied volatility in exchange-traded options associated with the Company’s common stock.

ACCRUED_EXPENSES_Tables

ACCRUED EXPENSES (Tables)	3 Months Ended
	Mar. 31, 2014
Payables And Accruals [Abstract]	'
Summary of Accrued Expenses	'
	The following table summarizes the Company’s accrued expenses for each of the periods indicated:
		As of		As of
		March 31,		December 31,
		2014		2013
		(in thousands)
	Accrued contract manufacturing costs	$	5,169	$	1,414
	Accrued facility-related costs		3,531		2,843
	Accrued contract research costs		2,623		2,785
	Accrued employee compensation costs		2,611		5,048
	Accrued professional fees		1,606		1,235
	Others		800		1,276
	Total accrued expenses	$	16,340	$	14,601

GOVERNMENT_CONTRACTS_Tables

GOVERNMENT CONTRACTS (Tables)	3 Months Ended
	Mar. 31, 2014
Contractors [Abstract]	'
Revenue from United States and European Union Governments Contracts and Other Revenue	'
	The following table summarizes the revenue for each of our contracts with the U.S. and E.U. governments for each of the periods indicated:
		For the Three Months Ended
		March 31,
		2014		2013
		(in thousands)
	July 2010 Contract (Ebola and Marburg IV)	$	4,064	$	2,614
	August 2012 Contract (Intramuscular)		—		1,806
	November 2012 SKIP-NMD Agreement (DMD)		1,365		54
	July 2013 Children’s National Medical Center (DMD)		659		—
	Total	$	6,088	$	4,474

STOCKBASED_COMPENSATION_Tables

STOCK-BASED COMPENSATION (Tables)	3 Months Ended
	Mar. 31, 2014
Summary of Stock Option Activity	'
	The following table summarizes the Company’s stock option activity for each of the periods indicated:
			For the Three Months Ended March 31,
			2014						2013
			Shares			Weighted			Shares			Weighted
						Average						Average
						Exercise						Exercise
						Price						Price
	Grants outstanding at beginning of the period			4,190,367		$	23.46			2,522,522		$	11.76
	Granted			1,185,265			26.83			242,320			28.76
	Exercised			(48,579	)		10.39			(64,390	)		8.97
	Canceled or expired			(53,715	)		30.26			(5,774	)		14.83
	Grants outstanding at end of the period			5,273,338		$	24.27			2,694,678		$	13.35
	Grants exercisable at end of the period			1,180,245		$	12.85			656,805		$	12.36
Summary of Restricted Stock Award Activity	'
	The following table summarizes the Company’s RSA activity for each of the periods indicated:
			For the Three Months Ended March 31,
			2014						2013
			Shares			Weighted			Shares			Weighted
						Average						Average
						Grant Date						Grant Date
						Fair Value						Fair Value
	Grants outstanding at beginning of the period			6,000		$	34.92			4,998		$	10.08
	Granted			6,000			29.03			—			—
	Grants outstanding at end of the period			12,000		$	31.98			4,998		$	10.08
Summary of Restricted Stock Unit Activity	'
	The following table summarizes the Company’s RSU activity for each of the periods indicated:
			For the Three Months Ended March 31,
			2014						2013
			Shares			Weighted			Shares			Weighted
						Average						Average
						Grant Date						Grant Date
						Fair Value						Fair Value
	Grants outstanding at beginning of the period			6,507		$	5.4			38,260		$	6.32
	Canceled or expired			—			—			(262	)		5.4
	Grants outstanding at end of the period			6,507		$	5.4			37,998		$	6.33
Summary of Stock Appreciation Rights Activity	'
	The following table summarizes the Company’s SAR activity for each of the periods indicated:
			For the Three Months Ended March 31,
			2014						2013
			Shares			Weighted			Shares			Weighted
						Average						Average
						Exercise						Exercise
						Price						Price
	Grants outstanding at beginning of the period			170,000		$	18.18			170,000		$	18.18
	Grants outstanding at end of the period			170,000		$	18.18			170,000		$	18.18
	Grants exercisable at end of the period			61,041		$	17.6			—		$	—
Summary of Share-based Compensation Expense by Function Included within Condensed Consolidated Statement of Operations and Comprehensive Loss	'
	The following table summarizes share-based compensation expense by function included within the unaudited condensed consolidated statements of operations and comprehensive loss:
			For the Three Months Ended March 31,
			2014			2013
	Research and development		$	1,873		$	530
	General and administrative			2,469			1,141
	Total		$	4,342		$	1,671
Summary of Share-based Compensation Expense by Grant Type Included within Condensed Consolidated Statement of Operations and Comprehensive Loss	'
	The following table summarizes share-based compensation expense by grant type included within the unaudited condensed consolidated statements of operations and comprehensive loss:
			For the Three Months Ended March 31,
			2014			2013
	Stock options		$	3,911		$	1,401
	Restricted stock awards			64			12
	Restricted stock units			(4	)		117
	Stock appreciation rights			147			141
	Employee stock purchase plan			224			—
	Total		$	4,342		$	1,671
Stock Options	'
Assumptions for Measuring Fair Values of Stocks	'
	The fair values of stock options granted during the periods presented were measured on the date of grant using the Black-Scholes-Merton option-pricing model, with the following assumptions:
			For the Three Months Ended March 31,
			2014			2013
	Risk-free interest rate (1)			1.7	%		0.7	%
	Expected dividend yield (2)			0	%		0	%
	Expected lives (3)			4.9 years			4.9 years
	Expected volatility (4)			95.4	%		80	%
	-1	The risk-free interest rate is estimated using an average of Treasury bill interest rates over a historical period commensurate with the expected term of the option that correlates to the prevailing interest rates at the time of grant.
	-2	The expected dividend yield is zero as the Company has not paid any dividends to date and does not expect to pay dividends in the future.
	-3	The expected lives are estimated using expected and historical exercise behavior.
	-4	The expected volatility is estimated using a blend of calculated volatility of the Company’s common stock over a historical period and implied volatility in exchange-traded options of the Company’s common stock.
Employee Stock Purchase Plan	'
Assumptions for Measuring Fair Values of Stocks	'
	The following table summarizes the assumptions used in the calculation during the period indicated:
			For the Three
			Months Ended
			March 31, 2014
	Fair value of stock purchase rights		$12.22 - 25.35
	Weighted-average stock price volatility		101% - 109%
	Expected lives		0.5 - 2 years
	Risk-free rate		0.1% - 0.3%

NET_LOSS_PER_SHARE_Tables

NET LOSS PER SHARE (Tables)	3 Months Ended
	Mar. 31, 2014
Earnings Per Share [Abstract]	'
Basic and Diluted Net Income (Loss) Per Share	'
			For the Three Months Ended March 31,
			2014			2013
			(in thousands, except per share amounts)
	Net loss		$	(28,273	)	$	(42,084	)
	Weighted-average number of shares of common stock and common stock equivalents outstanding:
	Weighted-average number of shares of common stock outstanding for computing basic earnings per share			37,821			31,813
	Dilutive effect of outstanding warrants and stock options after application of the treasury stock method*			—			—
	Weighted-average number of shares of common stock and dilutive common stock equivalents outstanding for computing diluted earnings per share			37,821			31,813
	Net loss per share — basic and diluted		$	(0.75	)	$	(1.32	)
	*	Warrants, stock options, restricted stock awards, restricted stock units and stock appreciation rights to purchase approximately 6,096,000 and 5,997,000 shares of common stock were excluded from the net loss per share calculation for the three months ended March 31, 2014 and 2013, respectively, as their effect would have been anti-dilutive.

RESTRUCTURING_Tables

RESTRUCTURING (Tables)	3 Months Ended
	Mar. 31, 2014
Restructuring And Related Activities [Abstract]	'
Changes in Liability and Balance Related to Restructuring Plan	'
	Changes in the liability and the balance related to the restructuring plan are as follows:
		For the Three Months Ended March 31,
		2014			2013
		(in thousands)
	Balance at beginning of the period	$	44		$	185
	Restructuring charges		9			462
	Payments		(8	)		(201	)
	Balance at end of the period	$	45		$	446

COMMITMENTS_AND_CONTINGENCIES_

COMMITMENTS AND CONTINGENCIES (Tables)	3 Months Ended
	Mar. 31, 2014
Commitments And Contingencies Disclosure [Abstract]	'
Aggregate Non-Cancelable Future Minimum Payments under Leases	'
	The aggregate non-cancelable future minimum payments under leases were as follows:
		As of
		March 31, 2014
		(in thousands)
	2014 (9 months)	$	2,790
	2015		3,807
	2016		3,895
	2017		3,986
	2018		4,079
	Thereafter		8,889
	Total minimum lease payments	$	27,446
Non-cancelable Contractual Obligations	'
	The following table presents non-cancelable contractual obligations arising from these arrangements:
		As of
		March 31, 2014
		(in thousands)
	2014 (9 months)	$	38,528
	2015		44,901
	2016		42,779
	2017		21,390
	2018		14,260
	Thereafter		3,565
	Total purchase commitments	$	165,423

Recovered_Sheet1

Business and Basis of Presentation - Additional Information (Detail) (USD $)	3 Months Ended					0 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013	Apr. 29, 2014
	Segment				Accounts Payable [Member]	Subsequent Event
Organization And Nature Of Business [Line Items]	'	'	'	'	'	'
Losses incurred during the period	$571,509,000	$543,236,000	'	'	'	'
Cash, cash equivalents and investments	233,100,000	'	'	'	'	'
Cash and cash equivalents	49,101,000	256,965,000	167,919,000	187,661,000	'	'
Short-term investments	176,091,000	'	'	'	'	'
Restricted investments	7,900,000	'	'	'	'	'
Common stock issued	'	'	'	'	'	2,650,000
Common stock offering price per share	'	'	'	'	'	$38
Proceeds from issuance of common stock	'	'	'	'	'	94,500,000
Number of operating segments	1	'	'	'	'	'
Accrued liabilities	16,340,000	14,601,000	'	'	9,600,000	'
Accrued employee compensation	'	'	$5,000,000	'	'	'

Accounts_Receivable_Additional

Accounts Receivable - Additional Information (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Government receivables unbilled amount	$5.50	$2.40
U.S. Government Audit [Member]	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Government receivables unbilled amount	$3.80	'

Assets_and_Liabilities_Measure

Assets and Liabilities Measured and Carried at Fair Value (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	$192,150	$192,897
Warrants	9,213	9,006
Total liabilities	9,213	9,006
Cash Equivalents	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	8,162	185,000
Commercial Paper	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	24,890	'
Government And Government Agency Bonds [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	88,745	'
Corporate Bonds	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	62,456	'
Certificates of Deposit	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	7,897	7,897
Level 1	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	8,809	192,897
Warrants	'	'
Total liabilities	'	'
Level 1 | Cash Equivalents	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	912	185,000
Level 1 | Commercial Paper	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	'	'
Level 1 | Government And Government Agency Bonds [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	'	'
Level 1 | Corporate Bonds	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	'	'
Level 1 | Certificates of Deposit	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	7,897	7,897
Level 2	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	183,341	'
Warrants	'	'
Total liabilities	'	'
Level 2 | Cash Equivalents	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	7,250	'
Level 2 | Commercial Paper	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	24,890	'
Level 2 | Government And Government Agency Bonds [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	88,745	'
Level 2 | Corporate Bonds	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	62,456	'
Level 2 | Certificates of Deposit	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	'	'
Level 3	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	'	'
Warrants	9,213	9,006
Total liabilities	9,213	9,006
Level 3 | Cash Equivalents	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	'	'
Level 3 | Commercial Paper	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	'	'
Level 3 | Government And Government Agency Bonds [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	'	'
Level 3 | Corporate Bonds	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	'	'
Level 3 | Certificates of Deposit	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total assets	'	'

Summary_of_Company_Cash_Cash_E

Summary of Company Cash , Cash Equivalents and Short-term Investments (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Cash and Cash Equivalents [Line Items]	'	'
Cash, cash equivalents and short-term investments, Amortized cost	$225,251	$256,965
Cash, cash equivalents and short-term investments, Gross unrealized gains	5	'
Cash, cash equivalents and short-term investments, Gross unrealized losses	-64	'
Cash, cash equivalents and short-term investments, Fair market value	225,192	256,965
Cash and Cash Equivalents	'	'
Cash and Cash Equivalents [Line Items]	'	'
Cash, cash equivalents and short-term investments, Amortized cost	49,101	256,965
Cash, cash equivalents and short-term investments, Gross unrealized gains	'	'
Cash, cash equivalents and short-term investments, Gross unrealized losses	'	'
Cash, cash equivalents and short-term investments, Fair market value	49,101	256,965
Short-term Investments	'	'
Cash and Cash Equivalents [Line Items]	'	'
Cash, cash equivalents and short-term investments, Amortized cost	176,150	'
Cash, cash equivalents and short-term investments, Gross unrealized gains	5	'
Cash, cash equivalents and short-term investments, Gross unrealized losses	-64	'
Cash, cash equivalents and short-term investments, Fair market value	176,091	'
Cash, Money Market Funds, Commercial Paper and Government and Government Agency Bonds [Member]	'	'
Cash and Cash Equivalents [Line Items]	'	'
Cash, cash equivalents and short-term investments, Amortized cost	49,101	'
Cash, cash equivalents and short-term investments, Gross unrealized gains	'	'
Cash, cash equivalents and short-term investments, Gross unrealized losses	'	'
Cash, cash equivalents and short-term investments, Fair market value	49,101	'
Commercial Paper	'	'
Cash and Cash Equivalents [Line Items]	'	'
Cash, cash equivalents and short-term investments, Amortized cost	24,892	'
Cash, cash equivalents and short-term investments, Gross unrealized gains	1	'
Cash, cash equivalents and short-term investments, Gross unrealized losses	-3	'
Cash, cash equivalents and short-term investments, Fair market value	24,890	'
Government And Government Agency Bonds [Member]	'	'
Cash and Cash Equivalents [Line Items]	'	'
Cash, cash equivalents and short-term investments, Amortized cost	88,755	'
Cash, cash equivalents and short-term investments, Gross unrealized gains	4	'
Cash, cash equivalents and short-term investments, Gross unrealized losses	-14	'
Cash, cash equivalents and short-term investments, Fair market value	88,745	'
Corporate Bonds	'	'
Cash and Cash Equivalents [Line Items]	'	'
Cash, cash equivalents and short-term investments, Amortized cost	62,503	'
Cash, cash equivalents and short-term investments, Gross unrealized gains	'	'
Cash, cash equivalents and short-term investments, Gross unrealized losses	-47	'
Cash, cash equivalents and short-term investments, Fair market value	62,456	'
Cash and Money Market Funds [Member]	'	'
Cash and Cash Equivalents [Line Items]	'	'
Cash, cash equivalents and short-term investments, Amortized cost	'	256,965
Cash, cash equivalents and short-term investments, Gross unrealized gains	'	'
Cash, cash equivalents and short-term investments, Gross unrealized losses	'	'
Cash, cash equivalents and short-term investments, Fair market value	'	$256,965

Summary_of_Companys_Property_a

Summary of Company's Property and Equipment (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Property, Plant and Equipment [Line Items]	'	'
Property and equipment, gross	$37,233	$32,377
Less accumulated depreciation	-17,103	-17,328
Property and equipment, net	20,130	15,049
Lab equipment	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment, gross	8,332	7,728
Office equipment	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment, gross	2,210	306
Software and computer equipment	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment, gross	2,955	1,126
Building	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment, gross	1,856	1,856
Leasehold improvements	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment, gross	21,359	10,058
Construction in progress	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment, gross	$521	$11,303

Property_and_Equipment_Additio

Property and Equipment - Additional Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Accounting Policies [Abstract]	'	'	'
Construction in progress	'	'	$11.30
Tenant improvement from the landlord	'	'	6.2
Depreciation expense	$0.40	$0.30	'

WeightedAverage_Assumptions_De

Weighted-Average Assumptions (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Class of Warrant or Right [Line Items]	'		'
Risk-free interest rate	0.10%	[1]	0.10%	[1]
Expected dividend yield	0.00%	[2]	0.00%	[2]
Shares underlying warrants classified as liabilities	633,740		3,093,676
Market value of stock at beginning of the period	$20.37		$25.80
Market value of stock at end of period	$24.03		$36.95
Minimum	'		'
Class of Warrant or Right [Line Items]	'		'
Expected lives	'3 months 18 days	[3]	'9 months 18 days	[3]
Expected volatility	101.81%	[4]	99.40%	[4]
Maximum	'		'
Class of Warrant or Right [Line Items]	'		'
Expected lives	'4 months 24 days	[3]	'1 year 4 months 24 days	[3]
Expected volatility	121.88%	[4]	110.70%	[4]
[1]	The risk-free interest rate is estimated using an average of U.S. Treasury bill interest rates that correlate to the prevailing interest rates at the valuation date.
[2]	The expected dividend yield is zero as the Company has not paid any dividends to date and does not expect to pay dividends prior to the expiration of the warrants.
[3]	The expected lives are based on the remaining contractual lives of the related warrants at the valuation date.
[4]	The expected volatility is estimated using a blend of calculated volatility of the Company's common stock over a historical period and implied volatility in exchange-traded options associated with the Company's common stock.

WeightedAverage_Assumptions_Pa

Weighted-Average Assumptions (Parenthetical) (Detail)	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Fair Value Disclosures [Abstract]	'		'
Expected dividend yield	0.00%	[1]	0.00%	[1]
[1]	The expected dividend yield is zero as the Company has not paid any dividends to date and does not expect to pay dividends prior to the expiration of the warrants.

Reconciliation_of_Change_in_Va

Reconciliation of Change in Value of Company's Warrants Liabilities (Detail) (USD $)	3 Months Ended		404 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014
Class of Warrant or Right [Line Items]	'	'	'
Beginning balance	$9,006	$65,193	'
Increase in value of warrants	3,251	26,906	92,246
Ending balance	9,213	91,077	9,213
Warrant	'	'	'
Class of Warrant or Right [Line Items]	'	'	'
Reclassification to stockholders' equity upon exercise of warrants	($3,044)	($1,022)	'

Summary_of_Warrant_Activity_De

Summary of Warrant Activity (Detail)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Warrants Outstanding Shares	'	'
Warrants outstanding at beginning of the period	791,508	3,127,618
Exercised	-157,768	-33,942
Warrants outstanding at end of the period	633,740	3,093,676
Warrants exercisable at end of the period	633,740	3,093,676
Weighted Average Exercise Price	'	'
Warrants outstanding at beginning of the period	10.5	8.48
Exercised	10.59	8.16
Warrants outstanding at end of the period	9.92	8.49
Warrants exercisable at end of the period	9.92	8.49

Summary_of_Companys_Warrants_O

Summary of Company's Warrants Outstanding (Detail)	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Class of Warrant or Right [Line Items]	'	'	'	'
Outstanding Warrants	633,740	791,508	3,093,676	3,127,618
Minimum of Price Range	'	'	'	'
Class of Warrant or Right [Line Items]	'	'	'	'
Warrants Outstanding, Issue Date	30-Jan-09	'	'	'
Exercise Price of warrants issued	6.96	'	'	'
Outstanding Warrants	129,768	'	'	'
Warrant expiration date	30-Jul-14	'	'	'
Maximum of Price Range	'	'	'	'
Class of Warrant or Right [Line Items]	'	'	'	'
Warrants Outstanding, Issue Date	25-Aug-09	'	'	'
Exercise Price of warrants issued	10.68	'	'	'
Outstanding Warrants	503,972	'	'	'
Warrant expiration date	31-Aug-14	'	'	'

Summary_of_Accrued_Expenses_De

Summary of Accrued Expenses (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Payables And Accruals [Abstract]	'	'
Accrued contract manufacturing costs	$5,169	$1,414
Accrued facility-related costs	3,531	2,843
Accrued contract research costs	2,623	2,785
Accrued employee compensation costs	2,611	5,048
Accrued professional fees	1,606	1,235
Others	800	1,276
Total accrued expenses	$16,340	$14,601

Revenue_from_United_States_and

Revenue from United States and European Union Governments Contracts and Other Revenue (Detail) (USD $)	3 Months Ended		404 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014
Revenue [Line Items]	'	'	'
U.S. and E.U. governments contract revenue	$6,088	$4,474	$193,855
July 2010 Contract (Ebola and Marburg IV)	'	'	'
Revenue [Line Items]	'	'	'
U.S. and E.U. governments contract revenue	4,064	2,614	'
August 2012 Agreement (Intramuscular administration)	'	'	'
Revenue [Line Items]	'	'	'
U.S. and E.U. governments contract revenue	'	1,806	'
November 2012 SKIP-NMD Agreement (DMD)	'	'	'
Revenue [Line Items]	'	'	'
U.S. and E.U. governments contract revenue	1,365	54	'
Children's National Medical Center	'	'	'
Revenue [Line Items]	'	'	'
U.S. and E.U. governments contract revenue	$659	'	'

Government_Contracts_Additiona

Government Contracts - Additional Information (Detail) (USD $)

3 Months Ended

404 Months Ended

1 Months Ended

3 Months Ended

0 Months Ended

3 Months Ended

1 Months Ended

3 Months Ended

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2014

Jul. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Aug. 29, 2012

Mar. 31, 2014

Mar. 31, 2013

Nov. 30, 2012

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2013

Phase two three four Marburg

Children's National Medical Center

Children's National Medical Center

Children's National Medical Center

July 2010 Contract (Ebola and Marburg IV)

July 2010 Contract (Ebola and Marburg IV)

August 2012 Agreement (Intramuscular administration)

August 2012 Agreement (Intramuscular administration)

August 2012 Agreement (Intramuscular administration)

November 2012 SKIP-NMD Agreement (DMD)

November 2012 SKIP-NMD Agreement (DMD)

November 2012 SKIP-NMD Agreement (DMD)

November 2012 SKIP-NMD Agreement (DMD)

Segment

Maximum

Accounts, Notes, Loans and Financing Receivable [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of segments

'

'

'

'

'

'

'

4

'

'

'

'

'

'

'

'

Period of performance spanning

'

'

'

'

'

'

'

'4 years

'

'

'

'

'

'

'

'

Estimated funding

'

'

'

$84,400,000

'

'

'

'

'

'

'

'

'

'

'

'

Agreement revenue

6,088,000

4,474,000

193,855,000

'

'

659,000

'

4,064,000

2,614,000

'

'

1,806,000

'

1,365,000

54,000

100,000

Advance payments received on contracts awarded

'

'

'

'

'

'

'

'

'

3,900,000

'

'

'

'

'

'

Agreement amount

'

'

'

'

$1,300,000

'

'

'

'

'

'

'

$2,500,000

'

'

'

Research and development study related activities period

'

'

'

'

'

'

'

'

'

'

'

'

'

'3 years

'

'

StockBased_Compensation_Additi

Stock-Based Compensation - Additional Information (Detail) (USD $)	3 Months Ended			0 Months Ended	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Feb. 28, 2014	Mar. 31, 2014
			Stock Options Granted, Beginning In January 2011	Employee Stock Purchase Plan	Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'	'
Share based compensation granted under plan vest period	'	'	'4 years	'	'
Term of award	'	'	'10 years	'	'
Percentage of closing price of common stock	'	'	'	'	85.00%
Common stock purchase	'	'	'	21,774	'
Proceeds from issuance of common stock	'	'	'	$500,000	'
Stock-based compensation expense	$4,342,000	$1,671,000	'	'	'

Summary_of_Stock_Option_Activi

Summary of Stock Option Activity (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Stock Option Shares	'	'
Grants outstanding at beginning of the period	4,190,367	2,522,522
Granted	1,185,265	242,320
Exercised	-48,579	-64,390
Canceled or expired	-53,715	-5,774
Grants outstanding at end of the period	5,273,338	2,694,678
Grants exercisable at end of the period	1,180,245	656,805
Weighted Average Exercise Price	'	'
Grants outstanding at Beginning of the period	$23.46	$11.76
Granted	$26.83	$28.76
Exercised	$10.39	$8.97
Canceled or expired	$30.26	$14.83
Grants outstanding at end of the period	$24.27	$13.35
Grants exercisable at end of the period	$12.85	$12.36

Assumptions_for_Measuring_Fair

Assumptions for Measuring Fair Values of Stocks (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Expected dividend yield	0.00%	'
Stock Options	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Risk-free interest rate	1.70%	0.70%
Expected dividend yield	0.00%	0.00%
Expected lives	'4 years 10 months 24 days	'4 years 10 months 24 days
Expected volatility	95.40%	80.00%
Employee Stock Purchase Plan | Minimum	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Risk-free interest rate	0.10%	'
Expected lives	'6 months	'
Fair value of stock purchase rights	12.22	'
Weighted-average stock price volatility	101.00%	'
Employee Stock Purchase Plan | Maximum	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Risk-free interest rate	0.30%	'
Expected lives	'2 years	'
Fair value of stock purchase rights	25.35	'
Weighted-average stock price volatility	109.00%	'

Assumptions_for_Measuring_Fair1

Assumptions for Measuring Fair Values of Stocks (Parenthetical) (Detail)	3 Months Ended
	Mar. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'
Expected dividend yield	0.00%

Summary_of_Restricted_Stock_Aw

Summary of Restricted Stock Award Activity (Detail) (Restricted Stock Awards (RSA), USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Restricted Stock Awards (RSA)	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Shares, Grants outstanding at beginning of the period	6,000	4,998
Shares, Granted	6,000	'
Shares, Grants outstanding at end of the period	12,000	4,998
Weighted Average Grant Date Fair Value per Share, Grants outstanding at beginning of the period	$34.92	$10.08
Weighted Average Grant Date Fair Value per Share, Granted	$29.03	'
Weighted Average Grant Date Fair Value per Share, Grants outstanding at end of the period	$31.98	$10.08

Summary_of_Restricted_Stock_Un

Summary of Restricted Stock Unit Activity (Detail) (Restricted Stock Units (RSU), USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Restricted Stock Units (RSU)	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Weighted Average Grant Date Fair Value per Share, Grants outstanding at beginning of the period	$5.40	$6.32
Weighted Average Grant Date Fair Value per Share, Canceled or expired	'	$5.40
Weighted Average Grant Date Fair Value per Share, Grants outstanding at end of the period	$5.40	$6.33
Shares, Grants outstanding at beginning of the period	6,507	38,260
Shares, Canceled or expired	'	-262
Shares, Grants outstanding at end of the period	6,507	37,998

Summary_of_Stock_Appreciation_

Summary of Stock Appreciation Rights Activity (Detail) (Stock Appreciation Rights, USD $)	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Stock Appreciation Rights	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'
Shares, Grants outstanding at beginning of the period	170,000	170,000	170,000	170,000
Shares, Grants outstanding at end of the period	170,000	170,000	170,000	170,000
Shares, Grants exercisable at end of the period	61,041	'	'	'
Weighted Average Exercise Price per Share, Grants outstanding at beginning of the period	$18.18	$18.18	$18.18	$18.18
Weighted Average Exercise Price per Share, Grants outstanding at end of the period	$18.18	$18.18	$18.18	$18.18
Weighted Average Exercise Price per Share, Grants exercisable at end of the period	$17.60	'	'	'

Summary_of_Sharebased_Compensa

Summary of Share-based Compensation Expense by Function Included within Condensed Consolidated Statement of Operations and Comprehensive Loss (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'
Share-based compensation expense	$4,342	$1,671
Research and Development Expenses [Member]	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'
Share-based compensation expense	1,873	530
General and Administrative Expenses [Member]	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'
Share-based compensation expense	$2,469	$1,141

Summary_of_Sharebased_Compensa1

Summary of Share-based Compensation Expense by Grant Type Included within Condensed Consolidated Statement of Operations and Comprehensive Loss (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'
Share-based compensation expense	$4,342	$1,671
Stock Options	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'
Share-based compensation expense	3,911	1,401
Restricted Stock Awards (RSA)	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'
Share-based compensation expense	64	12
Restricted Stock Units (RSU)	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'
Share-based compensation expense	-4	117
Stock Appreciation Rights	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'
Share-based compensation expense	147	141
Employee Stock Purchase Plan	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'
Share-based compensation expense	$224	'

Basic_and_Diluted_Net_Income_L

Basic and Diluted Net Income (Loss) Per Share (Detail) (USD $)	3 Months Ended				404 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013		Mar. 31, 2014
Earnings Per Share [Abstract]	'		'		'
Net loss	($28,273)		($42,084)		($571,509)
Weighted average number of shares of common stock and common stock equivalents outstanding:	'		'		'
Weighted-average number of shares of common stock outstanding for computing basic earnings per share	37,821		31,813		'
Dilutive effect of outstanding warrants and stock options after application of the treasury stock method	'	[1]	'	[1]	'
Weighted-average number of shares of common stock and dilutive common stock equivalents outstanding for computing diluted earnings per share	37,821		31,813		'
Net loss per share - basic and diluted	($0.75)		($1.32)		'
[1]	Warrants, stock options, restricted stock awards, restricted stock units and stock appreciation rights to purchase approximately 6,096,000 and 5,997,000 shares of common stock were excluded from the net loss per share calculation for the three months ended March 31, 2014 and 2013, respectively, as their effect would have been anti-dilutive.

Basic_and_Diluted_Net_Income_L1

Basic and Diluted Net Income (Loss) Per Share (Parenthetical) (Detail)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Earnings Per Share [Abstract]	'	'
Anti-dilutive securities excluded from computation of earning per share	6,096,000	5,997,000

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	Dec. 31, 2013
In Millions, unless otherwise specified
Income Tax Disclosure [Abstract]	'
Deferred tax assets, gross	$133.60

Restructuring_Additional_Infor

Restructuring - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended
In Thousands, unless otherwise specified	Nov. 30, 2012	Mar. 31, 2014	Mar. 31, 2013
	Position
Restructuring Cost and Reserve [Line Items]	'	'	'
Reduction in workforce, number of employees	21	'	'
Restructuring charge	'	$9	$462
Research and Development Expenses [Member]	'	'	'
Restructuring Cost and Reserve [Line Items]	'	'	'
Restructuring charge	'	100	300
General and Administrative Expenses [Member]	'	'	'
Restructuring Cost and Reserve [Line Items]	'	'	'
Restructuring charge	'	'	$200

Changes_in_Liability_and_Balan

Changes in Liability and Balance Related to Restructuring Plan (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Changes in the liability and the balance related restructuring plan	'	'
Balance at beginning of the period	$44	$185
Restructuring charges	9	462
Payments	-8	-201
Balance at end of the period	$45	$446

Recovered_Sheet2

Commitments and Contingencies - Additional Information (Detail) (USD $)

1 Months Ended

3 Months Ended

3 Months Ended

1 Months Ended

3 Months Ended

Nov. 30, 2013

Apr. 30, 2013

Feb. 28, 2013

Mar. 31, 2014

Mar. 31, 2013

Dec. 31, 2013

Mar. 31, 2014

Jan. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Jun. 30, 2013

sqft

CreditFacility

Assignors [Member]

Sublease [Member]

Sublease [Member]

Corvallis, Oregon [Member]

Lease Agreements [Member]

Lease Agreements [Member]

sqft

Commitments and Contingencies [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

Letters of credit amount issued

'

'

$7,300,000

'

'

'

'

'

'

'

'

$600,000

Lease agreement, expiration period

'

'

'

'

'

'

'

'

'

'

'7 years

'

Lease agreement, average base rent due current

'

'

'

3,807,000

'

'

'

'

'

'

2,400,000

'

Lease agreement, average annual base rent year two

'

'

'

3,895,000

'

'

'

'

'

'

2,400,000

'

Lease agreement, average annual base rent year three

'

'

'

3,986,000

'

'

'

'

'

'

2,400,000

'

Lease agreement, average annual base rent year four

'

'

'

4,079,000

'

'

'

'

'

'

2,400,000

'

Lease agreement, average base rent year five

'

'

'

'

'

'

'

'

'

'

2,400,000

'

Lease agreement, average base rent year six

'

'

'

'

'

'

'

'

'

'

2,400,000

'

Lease agreement, average base rent year seven

'

'

'

'

'

'

'

'

'

'

2,400,000

'

Additional rental space under amendment

15,077

'

'

'

'

'

'

15,077

'

'

'

'

Total rental space

61,453

'

'

'

'

'

'

'

'

'

'

'

Additional annual base rent

500,000

'

'

'

'

'

'

'

'

'

'

'

Percentage of annual increase in lease

2.50%

'

'

'

'

'

'

'

'

3.00%

'

'

Lease agreement period

'

'

'

'

'

'

'

'18 months

'18 months

'

'

'

Total subleases base rent

'

'

'

'

'

'

'

700,000

'

'

'

'

Annual base rent

'

'

'

'

'

'

'

'

'

900,000

'

'

Rent expense under leases

'

'

'

1,100,000

600,000

'

'

'

'

'

'

'

Notice period to terminate license agreements

'

'

'

'6 months

'

'

'

'

'

'

'

'

Royalty payments

'

'

'

100,000

100,000

'

'

'

'

'

'

'

Maximum royalty to Charley's Fund

'

'

'

3,400,000

'

'

'

'

'

'

'

'

Upfront and development milestone payments

'

'

'

0

0

'

'

'

'

'

'

'

Obligated to make milestone payments

'

'

'

23,400,000

'

'

'

'

'

'

'

'

Receivables under satisfaction of milestones

'

'

'

21,100,000

'

'

'

'

'

'

'

'

Upfront payments recognized under agreement

'

7,100,000

'

'

'

'

300,000

'

'

'

'

'

Development and commercial milestone payments

'

'

'

'

'

'

2,700,000

'

'

'

'

'

Lawsuit filling date

'

'

'

'January 2014

'

'

'

'

'

'

'

'

Law affected under lawsuit filling

'

'

'

'The complaints allege that the defendants violated the federal securities laws in connection with disclosures related to eteplirsen

'

'

'

'

'

'

'

'

Lawsuit claim amount

'

'

'

4,000,000

'

'

'

'

'

'

'

'

Certificate of deposit purchased

'

'

7,300,000

'

'

'

'

'

'

'

'

'

Certificate of deposit maturity date

'

'

'

'

'

'2014-05

'

'

'

'

'

'

Restricted investments

'

'

'

$7,250,000

'

$7,250,000

'

'

'

'

'

'

Number of letter of credit

'

'

2

'

'

'

'

'

'

'

'

'

Aggregate_NonCancelable_Future

Aggregate Non-Cancelable Future Minimum Payments under Leases (Detail) (USD $)	Mar. 31, 2014
In Thousands, unless otherwise specified
Debt Disclosure [Abstract]	'
2014 (9 months)	$2,790
2015	3,807
2016	3,895
2017	3,986
2018	4,079
Thereafter	8,889
Total minimum lease payments	$27,446

Noncancelable_Contractual_Obli

Non-cancelable Contractual Obligations (Detail) (USD $)	Mar. 31, 2014
In Thousands, unless otherwise specified
Commitments And Contingencies Disclosure [Abstract]	'
2014 (9 months)	$38,528
2015	44,901
2016	42,779
2017	21,390
2018	14,260
Thereafter	3,565
Total purchase commitments	$165,423

Subsequent_Event_Additional_In

Subsequent Event - Additional Information (Detail) (Subsequent Event, USD $)	0 Months Ended
In Millions, except Share data, unless otherwise specified	Apr. 29, 2014
Subsequent Event	'
Subsequent Event [Line Items]	'
Common stock issued	2,650,000
Common stock offering price per share	$38
Options granted, number of shares	397,500
Proceeds from issuance of common stock	$94.50