Agios Pharmaceuticals (AGIO) 10-Q7 Nov 142014 Q3 Quarterly reportFinancial data

Company Profile

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
Document and Entity Information	Sep. 30, 2014	Nov. 06, 2014
Document And Entity Information [Abstract]	'	'
Document Type	'10-Q	'
Amendment Flag	'false	'
Document Period End Date	30-Sep-14	'
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q3	'
Trading Symbol	'AGIO	'
Entity Registrant Name	'AGIOS PHARMACEUTICALS INC	'
Entity Central Index Key	'0001439222	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Non-accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	34,683,082

Condensed_Consolidated_Balance

Condensed Consolidated Balance Sheets (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Current assets:	'	'
Cash and cash equivalents	$70,049	$71,560
Marketable securities	149,921	95,209
Collaboration receivable - related party	18,759	476
Prepaid expenses and other current assets	4,990	2,502
Refundable income taxes	3,841	'
Total current assets	247,560	169,747
Marketable securities	17,917	27,125
Property and equipment, net	3,677	3,758
Restricted cash	'	571
Other assets	454	4
Total assets	269,608	201,205
Current liabilities:	'	'
Accounts payable	6,225	3,678
Accrued expenses	10,004	6,586
Income taxes payable	'	1,462
Deferred revenue- related party	18,847	25,072
Deferred rent	'	123
Other current liabilities	8	9
Total current liabilities	35,084	36,930
Deferred revenue, net of current portion - related party	26,352	32,567
Deferred rent, net of current portion	423	220
Other non-current liabilities	'	6
Commitments and contingencies	'	'
Stockholders' equity:	'	'
Preferred stock, $0.001 par value; 25,000,000 shares authorized; no shares issued and outstanding	0	0
Common stock, $0.001 par value; 125,000,000 shares authorized; 34,642,539 and 31,202,542 shares issued and outstanding at September 30, 2014 and December 31, 2013, respectively	35	31
Additional paid-in capital	347,947	244,881
Accumulated other comprehensive income	51	14
Accumulated deficit	-140,284	-113,444
Total stockholders' equity	207,749	131,482
Total liabilities and stockholders' equity	$269,608	$201,205

Condensed_Consolidated_Balance1

Condensed Consolidated Balance Sheets (Parenthetical) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]	'	'
Preferred stock, par value	$0.00	$0.00
Preferred stock, shares authorized	25,000,000	25,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$0.00	$0.00
Common stock, shares authorized	125,000,000	125,000,000
Common stock, shares issued	34,642,539	31,202,542
Common stock, shares outstanding	34,642,539	31,202,542

Condensed_Consolidated_Stateme

Condensed Consolidated Statements of Operations (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Statement [Abstract]	'	'	'	'
Gross Collaboration revenue - related party	$33,900	$6,268	$50,722	$18,804
Operating expenses:	'	'	'	'
Research and development	25,526	14,803	65,509	39,223
General and administrative	5,166	2,534	12,619	6,222
Total operating expenses	30,692	17,337	78,128	45,445
Income (loss) from operations	3,208	-11,069	-27,406	-26,641
Interest income	48	13	118	26
Income (loss) before (benefit) provision for income taxes	3,256	-11,056	-27,288	-26,615
(Benefit) provision for income taxes	-448	121	-448	410
Net income (loss)	3,704	-11,177	-26,840	-27,025
Cumulative preferred stock dividends	'	-567	'	-4,162
Net income (loss) applicable to common stockholders	$3,704	($11,744)	($26,840)	($31,187)
Net income (loss) per share applicable to common stockholders - basic	$0.11	($0.52)	($0.81)	($3.08)
Net income (loss) per share applicable to common stockholders - diluted	$0.10	($0.52)	($0.81)	($3.08)
Weighted-average number of common shares used in net income (loss) per share applicable to common stockholders - basic	34,495,076	22,744,486	33,176,801	10,111,735
Weighted-average number of common shares used in net income (loss) per share applicable to common stockholders - diluted	36,592,683	22,744,486	33,176,801	10,111,735

Condensed_Consolidated_Stateme1

Condensed Consolidated Statements of Comprehensive Income (Loss) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]	'	'	'	'
Net income (loss)	$3,704	($11,177)	($26,840)	($27,025)
Other comprehensive income:	'	'	'	'
Unrealized gain on available-for-sale securities	39	30	37	27
Comprehensive income (loss)	$3,743	($11,147)	($26,803)	($26,998)

Condensed_Consolidated_Stateme2

Condensed Consolidated Statements of Cash Flows (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Operating activities	'	'
Net loss	($26,840)	($27,025)
Adjustments to reconcile net loss to net cash used in operating activities:	'	'
Depreciation	1,005	1,100
Stock-based compensation expense	6,778	1,865
Net amortization of premium on investments	412	81
Changes in operating assets and liabilities:	'	'
Collaboration receivable - related party	-18,283	'
Prepaid expenses and other assets	-2,756	-1,684
Accounts payable	2,354	-1,178
Accrued expenses and other liabilities	3,414	2,480
Deferred rent	80	'
Refundable income taxes and income taxes payable	-5,303	382
Deferred revenue - related party	-12,439	-18,804
Net cash used in operating activities	-51,578	-42,783
Investing activities	'	'
Purchases of marketable securities	-215,383	-119,498
Proceeds from maturities and sales of marketable securities	169,505	53,766
Purchases of property and equipment	-727	-1,075
Release of restricted cash	571	'
Net cash used in investing activities	-46,034	-66,807
Financing activities	'	'
Proceeds from public offering of common stock, net of commissions and offering costs	94,685	124,204
Net proceeds from stock option exercises and issuance of common stock	1,416	100
Net cash provided by financing activities	96,101	124,304
Net increase (decrease) in cash and cash equivalents	-1,511	14,714
Cash and cash equivalents at beginning of the period	71,560	91,297
Cash and cash equivalents at end of the period	70,049	106,011
Supplemental disclosure of non-cash investing and financing transactions	'	'
Additions to property, plant and equipment included in accounts payable	197	'
Vesting of restricted stock	-7	'
Conversion of convertible preferred stock into common stock	'	115,923
Public offering costs included in accounts payable	'	474
Proceeds from stock option exercises in other current assets	184	'
Supplemental cash flow information	'	'
Cash paid for income taxes	$5,958	'

Overview_and_Basis_of_Presenta

Overview and Basis of Presentation	9 Months Ended
Overview and Basis of Presentation	Sep. 30, 2014
Accounting Policies [Abstract]	'
Overview and Basis of Presentation	'
	1. Overview and Basis of Presentation
	Agios Pharmaceuticals, Inc. (“Agios” or “the Company”) is a biopharmaceutical company committed to the fundamental transformation of patients’ lives through scientific leadership in the field of cancer metabolism and rare genetic disorders of metabolism. The Company has built a unique set of core capabilities in the field of cellular metabolism, with the goal of making transformative, first or best in class medicines. The Company’s therapeutic areas of focus are cancer and rare genetic disorders of metabolism, which are a broad group of more than 600 rare genetic diseases caused by mutations, or defects, of single metabolic genes. In both of these areas, the Company is seeking to unlock the biology of cellular metabolism to create transformative therapies. The Company is located in Cambridge, Massachusetts.
	The condensed consolidated interim balance sheet as of September 30, 2014, the condensed consolidated interim statements of operations and comprehensive income (loss) for the three and nine months ended September 30, 2014 and 2013 and the statements of cash flows for the nine months ended September 30, 2014 and 2013, are unaudited. The unaudited condensed consolidated interim financial statements have been prepared on the same basis as the annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary to present fairly the Company’s condensed consolidated financial position as of September 30, 2014, and its results of operations for the three and nine months ended September 30, 2014 and 2013 and cash flows for the nine months ended September 30, 2014 and 2013. The financial data and the other financial information disclosed in these notes to the condensed consolidated interim financial statements related to the three and nine month periods are also unaudited. The results of operations for the three and nine months ended September 30, 2014 are not necessarily indicative of the results to be expected for the year ending December 31, 2014 or for any other future annual or interim period. The condensed consolidated interim financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2013 that was filed with the Securities and Exchange Commission (the “SEC”) on March 18, 2014.
	The Company’s condensed consolidated financial statements include the Company’s accounts and the accounts of the Company’s wholly-owned subsidiary, Agios Securities Corporation. All intercompany transactions have been eliminated in consolidation. The condensed consolidated interim financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”).
	On July 29, 2013, the Company closed an initial public offering (“IPO”) of its common stock, which resulted in the sale of 6,772,221 shares of its common stock at a public offering price of $18.00 per share, before underwriting commissions and discounts, including 883,333 shares of common stock issued upon the exercise in full by the underwriters of their option to purchase additional shares at the public offering price to cover over-allotments. The Company received net proceeds from the IPO of $111.0 million, after deducting underwriting discounts, commissions, and expenses payable by the Company. Additionally, an affiliate of Celgene Corporation (“Celgene”), the Company’s cancer metabolism strategic alliance partner, purchased 708,333 shares of common stock in a separate private placement concurrent with the completion of the IPO at a purchase price of $18.00 per share for aggregate proceeds of $12.8 million.
	In connection with preparing for the IPO, the Company’s Board of Directors and stockholders approved a 1-for-2.75 reverse stock split of the Company’s common stock. The reverse stock split became effective on July 11, 2013. All share and per share amounts in the condensed consolidated interim financial statements and notes thereto have been retroactively adjusted for all periods presented to give effect to this reverse stock split, including reclassifying an amount equal to the reduction in par value of common stock to additional paid-in capital. In connection with the closing of the IPO, all of the Company’s outstanding convertible preferred stock automatically converted to common stock as of July 29, 2013, resulting in an additional 19,731,564 shares of common stock of the Company becoming outstanding.
	In April 2014, the Company completed a public offering of 2,000,000 shares of its common stock at a public offering price of $44.00 per share, before underwriting commissions and discounts. The Company received net proceeds from this offering of $82.3 million, after deducting underwriting discounts, commissions and expenses payable by the Company. Celgene purchased 294,800 shares of the Company’s common stock in the offering. In addition, the Company granted the underwriters the right to purchase up to an additional 300,000 shares of its common stock which was exercised in May 2014 resulting in additional net proceeds to the Company of $12.4 million, after underwriting discounts and commissions paid by the Company.

Summary_of_Significant_Account

Summary of Significant Accounting Policies and Recent Accounting Pronouncements	9 Months Ended
	Sep. 30, 2014
Accounting Policies [Abstract]	'
Summary of Significant Accounting Policies and Recent Accounting Pronouncements	'

	2. Summary of Significant Accounting Policies and Recent Accounting Pronouncements

	In July 2014, the Company amended its collaboration agreement with Celgene. As a result of the amendment, the Company was required to reevaluate the agreement under Financial Accounting Standards Board (“FASB”) Accounting Standards Update (“ASU”) No. 2009-13, Multiple-Element Revenue Arrangements (“ASU No. 2009-13”). The amendment was determined to be a material modification pursuant to ASU No. 2009-13, and the Company will recognize revenue for the arrangement under this guidance on a prospective basis, as discussed in Note 5.

	There have been no other material changes to the significant accounting policies previously disclosed in the Annual Report on Form 10-K for the year ended December 31, 2013.

	In August 2014, the FASB issued ASU No. 2014-15, Presentation of Financial Statements—Going Concern (Subtopic 205-40). The ASU requires all entities to evaluate for the existence of conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the issuance date of the financial statements. The accounting standard is effective for interim and annual periods ending after December 15, 2016, and will not have a material impact on the consolidated financial statements, but may impact the Company’s footnote disclosures.

	In June 2014, the FASB issued ASU No. 2014-12, Compensation—Stock Compensation (Topic 718). The ASU clarifies how entities should treat performance targets that can be achieved after the requisite service period of a share-based payment award. The accounting standard is effective for interim and annual periods beginning after December 15, 2015 and is not expected to have a material impact on the consolidated financial statements.

	In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606). The ASU provides for a single comprehensive model for use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance. The accounting standard is effective for interim and annual periods beginning after December 15, 2016 with no early adoption permitted. The Company is required to adopt the amendments in the ASU using one of two acceptable methods. The Company is currently in the process of determining which adoption method it will apply evaluating the impact of the guidance on its consolidated financial statements.

	Other accounting standards that have been issued by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on the Company’s financial statements upon adoption.

Fair_Value_Measurements

Fair Value Measurements	9 Months Ended
Fair Value Measurements	Sep. 30, 2014
Fair Value Disclosures [Abstract]	'
Fair Value Measurements	'

	3. Fair Value Measurements

	The Company records cash equivalents and marketable securities at fair value. Accounting Standards Codification (“ASC”) Topic 820, Fair Value Measurements and Disclosures, established a fair value hierarchy for those instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and the Company’s own assumptions (unobservable inputs). The hierarchy consists of three levels:

	Level 1 – Unadjusted quoted prices in active markets for identical assets or liabilities.

	Level 2 – Quoted prices for similar assets and liabilities in active markets, quoted prices in markets that are not active, or inputs which are observable, either directly or indirectly, for substantially the full term of the asset or liability.

	Level 3 – Unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability in which there is little, if any, market activity for the asset or liability at the measurement date.

	The following table summarizes the cash equivalents and marketable securities measured at fair value on a recurring basis as of September 30, 2014 (in thousands):



		Level 1		Level 2		Level 3		Total
	Cash equivalents	$	69,245	$	480	$	—	$	69,725
	Marketable securities:
	Certificates of deposit		—		14,521		—		14,521
	U.S. Treasuries		153,317		—		—		153,317

		$	222,562	$	15,001	$	—	$	237,563




	The following table summarizes the cash equivalents and marketable securities measured at fair value on a recurring basis as of December 31, 2013 (in thousands):



		Level 1		Level 2		Level 3		Total
	Cash equivalents	$	68,792	$	—	$	—	$	68,792
	Marketable securities:
	Certificates of deposit		—		6,915		—		6,915
	U.S. Treasuries		115,419		—		—		115,419

		$	184,211	$	6,915	$	—	$	191,126


	Cash equivalents and marketable securities have been initially valued at the transaction price and subsequently valued, at the end of each reporting period, utilizing third-party pricing services or other market observable data. The pricing services utilize industry standard valuation models, including both income and market based approaches and observable market inputs to determine value. The Company validates the prices provided by its third-party pricing services by reviewing their pricing methods and obtaining market values from other pricing sources. After completing its validation procedures, the Company did not adjust or override any fair value measurements provided by the pricing services as of September 30, 2014 or December 31, 2013.

	There have been no changes to the valuation methods during the three or nine months ended September 30, 2014 and 2013. The Company evaluates transfers between levels at the end of each reporting period. There were no transfers of assets or liabilities between Level 1 and Level 2 during the three and nine months ended September 30, 2014 or the year ended December 31, 2013. The Company had no financial assets or liabilities that were classified as Level 3 at any point during the nine months ended September 30, 2014 or the year ended December 31, 2013.

Marketable_Securities

Marketable Securities	9 Months Ended
Marketable Securities	Sep. 30, 2014
Investments, Debt and Equity Securities [Abstract]	'
Marketable Securities	'

	4. Marketable Securities

	Marketable securities at September 30, 2014 and December 31, 2013 consisted primarily of investments in United States Treasuries and certificates of deposit. Management determines the appropriate classification of the securities at the time they are acquired and evaluates the appropriateness of such classifications at each balance sheet date. The Company classifies its marketable securities as available-for-sale pursuant to ASC 320, Investments – Debt and Equity Securities. Marketable securities are recorded at fair value, with unrealized gains and losses included as a component of accumulated other comprehensive income in stockholders’ equity and a component of total comprehensive income (loss) in the condensed consolidated interim statements of comprehensive income (loss), until realized. Realized gains and losses are included in investment income on a specific-identification basis. There were no realized gains or losses on marketable securities for the three or nine months ended September 30, 2014 and 2013.

	The Company reviews marketable securities for other-than-temporary impairment whenever the fair value of a marketable security is less than the amortized cost and evidence indicates that a marketable security’s carrying amount is not recoverable within a reasonable period of time. Other-than-temporary impairments of investments are recognized in the condensed consolidated interim statements of operations if the Company has experienced a credit loss, has the intent to sell the marketable security, or if it is more likely than not that the Company will be required to sell the marketable security before recovery of the amortized cost basis. Evidence considered in this assessment includes reasons for the impairment, compliance with the Company’s investment policy, the severity and the duration of the impairment and changes in value subsequent to the end of the period.

	Marketable securities at September 30, 2014 consist of the following (in thousands):



		Amortized Cost		Unrealized		Unrealized			Fair
		Amortized Cost		Gains		Losses			Value
	Current:
	Certificates of deposit	$	14,530	$	—	$	(9	)	$	14,521
	U.S. Treasuries		135,348		53		(1	)		135,400
	Non-current:
	U.S. Treasuries		17,909		8		—			17,917

		$	167,787	$	61	$	(10	)	$	167,838




	Marketable securities at December 31, 2013 consist of the following (in thousands):



		Amortized Cost		Unrealized		Unrealized			Fair
		Amortized Cost		Gains		Losses			Value
	Current:
	Certificates of deposit	$	6,920	$	—	$	(5	)	$	6,915
	U.S. Treasuries		88,287		8		(1	)		88,294
	Non-current:
	U.S. Treasuries		27,113		12		—			27,125

		$	122,320	$	20	$	(6	)	$	122,334


	At September 30, 2014 and December 31, 2013, the Company held both current and non-current investments. Investments classified as current have maturities of less than one year. Investments classified as non-current are those that (i) have maturities of one to two years and (ii) management does not intend to liquidate within the next twelve months, although these funds are available for use and therefore classified as available-for-sale.

	At September 30, 2014 and December 31, 2013, the Company held 60 and 33 debt securities that were in an unrealized loss position for less than one year, respectively. The aggregate fair value of debt securities in an unrealized loss position at September 30, 2014 and December 31, 2013 was $21.5 million and $31.7 million, respectively. There were no individual securities that were in a significant unrealized loss position as of September 30, 2014 and December 31, 2013. The Company evaluated its securities for other-than-temporary impairment and considered the decline in market value for the securities to be primarily attributable to current economic and market conditions. It is not more likely than not that the Company will be required to sell the securities, and the Company does not intend to do so prior to the recovery of the amortized cost basis. Based on this analysis, these marketable securities were not considered to be other-than-temporarily impaired as of September 30, 2014 and December 31, 2013.

Collaboration_Agreements

Collaboration Agreements	9 Months Ended
	Sep. 30, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
Collaboration Agreements	'

	5. Collaboration Agreements

	Celgene

	In April 2010, the Company entered into a collaboration agreement focused on cancer metabolism with Celgene, a related party through ownership of the Company’s common stock. The agreement was amended in October 2011 and in July 2014, as described below. The goal of the collaboration is to discover, develop and commercialize disease-altering therapies in oncology based on the Company’s cancer metabolism research platform. The Company is leading discovery, preclinical and early clinical development for all cancer metabolism programs under the collaboration. The discovery phase of the amended collaboration was to expire in April 2014, subject to Celgene’s option to extend the discovery phase for up to an additional two years with additional funding to the Company. In December 2013, Celgene elected to extend the term of the initial discovery phase from four years to five years, to April 2015. Celgene has the ability to extend the term of the discovery phase for one additional year to April 2016 for the payment of a $20.0 million extension fee.

	Pursuant to the collaboration agreement and subsequent amendments, the Company was responsible for nominating development candidates, of which two required confirmation by the Joint Research Committee (“JRC”) during the discovery phase. During the year ended December 31, 2012 the Company nominated its first development candidate and during the year ended December 31, 2013 the Company nominated its second development candidate, both of which have been confirmed by the JRC pursuant to the agreement. For each development candidate, Celgene elected to progress such development candidate into preclinical development requiring the Company to conduct studies to meet the requirements for filing an Investigational New Drug application (“IND”), or IND-enabling studies. Subsequently, the Company was required to file INDs for each development candidate and, upon the FDA’s acceptance of the INDs, Celgene requested that the Company conduct initial phase 1 studies.



	Celgene may elect to convert each discovery program for which the Company has nominated a development candidate into a co-commercialized licensed program, the attributes of which are described below. The Company has the right, exercisable during a specified period following FDA acceptance of the applicable IND, to convert one of every three co-commercialized licensed programs into a split licensed program, for which the Company will retain the United States rights, other attributes of which are further described below. In June 2014, Celgene exercised its option to an exclusive global license for the development and commercialization of the Company’s isocitrate dehydrogenase 2 (“IDH2”) program, AG-221. The Company elected to retain U.S. rights to its isocitrate dehydrogenase 1 (“IDH1”) program, AG-120, in January 2014. If Celgene exercises its rights to this program, the program will become a split licensed program. In addition, Celgene may license certain discovery programs that the Company does not nominate or the JRC does not confirm as a development candidate and for which Celgene will lead and fund global development and commercialization.

	The Company will retain the rights to development candidates and certain other compounds that Celgene does not elect to progress into preclinical development or convert into a co-commercialized licensed program. In addition, if the JRC or Celgene elects not to continue collaboration activities with respect to a particular target, either the Company or Celgene would have the right to independently undertake a discovery program on such target and would have rights to specified compounds from such program, subject to certain “buy-in” rights granted to the other party.

	The agreement provides for three types of licensed programs as discussed above:

	Co-Commercialized Licensed Programs: Celgene will lead and, following either IND acceptance by the FDA or, if Celgene requests the Company to conduct the initial phase 1 study upon completion of such phase 1 study, will fund global development and commercialization. The Company has the right to participate in a portion of sales activities in the United States for products from co-commercialized programs in accordance with the applicable commercialization plan. The Company will be eligible to receive milestone payments and royalties arising from the licensed program.

	Split Licensed Programs: Celgene will lead development and commercialization outside the United States and the Company will lead development and commercialization in the United States. The Company and Celgene will equally fund the global development costs of each split licensed program that are not specific to any particular region or country, Celgene will be responsible for development and commercialization costs specific to countries outside the United States, and the Company will be responsible for development and commercialization costs specific to the United States. The Company will retain profits generated in the United States and will also be eligible to receive milestone payments and royalties arising from net sales outside the United States. The Company will be obligated to pay Celgene royalties arising from net sales in the United States.

	Buy-In Programs: If a party elects to independently undertake a discovery program, with respect to a particular target under the agreement, the party that is conducting the independent program that becomes a buy-in program will lead the development and commercialization of such program. The party that elects to buy in to such program will be responsible for funding a portion of development costs incurred after acceptance of an IND for a buy-in program compound, and the lead party will be responsible for all other development costs and all commercialization costs for products from such buy-in program. The commercializing party will be obligated to pay the buy-in party specified royalties on worldwide net sales.

	The term of the agreement will continue, unless earlier terminated by either party, until the expiration of the last-to-expire of all royalty terms with respect to all royalty-bearing products. Celgene may terminate the agreement for convenience in its entirety or with respect to one or more programs upon thirty days written notice to the Company. Either the Company or Celgene may terminate the agreement in its entirety or with respect to one or more programs, if the other party is in material breach and fails to cure such breach within the specified cure period; however, if such breach relates solely to a specific program, the non-breaching party may only terminate the agreement with respect to such program. Either the Company or Celgene may terminate the agreement in the event of specified insolvency events involving the other party.

	Under the terms of the agreement, the Company received an upfront payment of approximately $121.2 million. In addition, Celgene purchased 5,190,551 shares of Series B convertible preferred stock (“Series B Preferred Stock”) at a price of $1.70 per share, resulting in net proceeds to the Company of approximately $8.8 million. The Company determined the price paid by Celgene for the Series B Preferred Stock represented a premium over the fair value of the Company’s Series B Preferred Stock as determined by the implied value of the Series B Preferred Stock pursuant to a contemporaneous valuation analysis that allocated the equity value of the Company to the various classes of its then-outstanding securities. The Company accounted for the $3.1 million premium as additional consideration under the agreement and the Series B Preferred Stock was recorded at its fair value of $5.7 million. In connection with the 1-for-2.75 reverse stock split of the Company’s common stock, the shares of Series B Preferred Stock converted into 1,887,473 shares of common stock upon the closing of the Initial Public Offering in July 2013.



	In October 2011, the agreement was amended to extend the term of the initial discovery period from three to four years, to April 2014. The amendment was not deemed to be a material modification to the arrangement, pursuant to ASU No. 2009-13, since there were no changes in the deliverables or the total arrangement consideration, as the provisions of the original agreement provided Celgene with the option to extend the research period for the same consideration. Celgene made a payment to the Company of $20.0 million pursuant to the amendment. The payment was combined with the unamortized upfront payment and premium and was recognized as revenue on a straight-line basis over the estimated performance period prior to the July 2014 amendment described below.

	In December 2013, Celgene elected to extend the term of the initial discovery period from four to five years, to April 2015. As a result of the extension, the Company received a $20.0 million extension payment from Celgene in May 2014. The payment was combined with the unamortized upfront payment, premium, and prior extension payment and was being recognized as revenue on a straight-line basis over the estimated performance period prior to the July 2014 amendment described below. The Company is also eligible to receive an additional $20.0 million extension payment in the event Celgene elects to extend the discovery phase until April 2016.

	In July 2014, the Company amended the collaboration agreement to allow for more flexibility in the design and conduct of phase 1 clinical trials and additional nonclinical and/or clinical activities that the Company agrees to perform at Celgene’s request. The amendment further modifies the mechanism and timing for payments to be made with respect to such development activities. The amendment was determined to be a material modification pursuant to ASU No. 2009-13, due to a change in the total potential consideration that was more than insignificant and changes to certain of the deliverables in the arrangement. The amendment impacts the co-commercialized and split licensed programs as follows:


		•	Co-commercialized licensed programs: The amendment modifies the timing and nature of the consideration for the development efforts related to an initial phase 1 study from a milestone due at the completion of the study to payments due upon the earlier of the determination of the maximum tolerated dose or Celgene’s election to license the program.


		•	Split licensed programs: The amendment allows for the Company to receive reimbursement for costs and expenses it incurs for any disease-specific expansion cohort within a phase 1 clinical trial design, provided that the disease-specific expansion cohort supports the initiation of a subsequent pivotal clinical trial. The milestone reimbursement is the lesser of fifty percent of the costs incurred by the Company for disease specific cohorts and $10 million and is payable upon the first patient dosed within the corresponding pivotal trial.

	Prior to the amendment, the Company concluded that none of the identified deliverables had stand-alone value and, therefore, accounted for the deliverables as a single unit of accounting. The Company further concluded it was unable to estimate the fair value of the undelivered items within the agreement. Consideration received was recognized on a straight-line basis through the period over which the Company expected to fulfill its performance obligations (the performance period), which was initially determined to be 6 years.

	Upon concluding the arrangement had been materially modified in July 2014, the Company identified the remaining deliverables under the arrangement and determined its best estimate of selling price for the undelivered elements as of the modification date. The Company then allocated the total arrangement consideration, which included the remaining deferred revenue balance at the modification date and other consideration that was deemed to be determinable at the modification date, to each unit of accounting based on its best estimate of selling price. The difference between the total allocable consideration and the best estimate of selling price of the undelivered items was recorded as revenue at the modification date. The undelivered items, which are each considered by the Company to have stand-alone value and therefore are separate units of accounting, the related best estimate of selling price, and the method of recognizing the allocated consideration, for each unit of accounting are as follows:


		•	License for the split licensed program – AG-120: The Company developed the best estimate of selling price of the license by probability weighting multiple cash flow scenarios using the income approach. Management estimates within the models include the expected, probability-weighted net profits from estimated future sales, an estimated royalty rate using comparable industry royalty agreements, an estimate of the direct cost incurred to generate future cash flows, a discount rate, an estimated contributory asset charge rate to reflect the cost associated with the use of other assets to generate the cash flow, an estimated income tax rate and other business forecast factors. There are significant judgments and estimates inherent in the determination of the best estimate of selling price of this unit of accounting. These judgments and estimates include assumptions regarding future operating performance, the timelines of the clinical trials and regulatory approvals and the estimated patient populations. Should different reasonable assumptions be utilized, the best estimate of selling price and the associated revenues recognized would be different. Based on the analysis using management’s best estimate, the Company allocated $21.2 million to the license and will recognize revenue upon Celgene’s election to exercise its option to the split licensed program – AG-120. The Company will immediately recognize the allocated consideration received to date on the exercise date; however, the Company is unable to determine when Celgene will elect to exercise its option to obtain the license.


		•	Development services for five separate on-going phase 1 studies (each of which is a separate unit of accounting): The Company developed the best estimate of selling price of the on-going phase 1 study development services of $50.8 million for all five studies using management’s best estimate of the cost of obtaining these services from a third-party provider. The estimated costs were determined to represent management’s best estimate of the price these services could be sold for separately, as well as internal full time equivalent costs to support the development services. The amount allocated to these units of accounting will be recognized as revenue on a proportional performance basis as services are provided. The Company expects the performance period for these units of accounting to be delivered through the second quarter of 2016.


		•	On-going research and development: The Company developed the best estimate of selling price of the research and development services of $13.6 million using management’s best estimate of the cost of obtaining these services from a third-party provider. The amount allocated to this unit of accounting will be recognized as revenue ratably over the performance period. The performance period has been determined to be through April 2015.


		•	Committee participation: The Company developed the best estimate of selling price of the committee participation services of $0.2 million using management’s best estimate of the anticipated participation hours multiplied by a market rate for comparable participants. The amount allocated to this unit of accounting will be recognized as revenue ratably over the performance period. The performance period has been determined to be through April 2015.

	The allocable consideration will increase as the Company performs certain services for which it is eligible to receive additional consideration. These amounts will be recognized on a cumulative catch-up basis for any in-process units of accounting or immediately for any fully delivered units of accounting.

	For the period January 1, 2014 through the amendment date, the Company recognized a total of $42.7 million in revenues under the previous accounting guidance and upon the modification. The Company recognized $8.0 million in revenues subsequent to the modification date. The Company recognized total revenues of $33.9 million and $50.7 million in connection with the Celgene collaboration during the three and nine months ended September 30, 2014, respectively. In determining the current and noncurrent classification of deferred revenue, the Company considers the total consideration expected to be earned in the next twelve months for services to be performed under certain units of accounting and the estimated proportional performance and timing of delivery of certain deliverables to determine the deferred revenue balance that will remain twelve months from the balance sheet date.



The Company recorded revenue of approximately $6.3 million and $18.8 million in connection with the Celgene collaboration during the three and nine months ended September 30, 2013, respectively.

Under the arrangement, the Company is eligible to receive up to $120.0 million in potential milestone payments payable for each program selected by Celgene. The potential milestone payments for each such program are comprised of: (i) a $25.0 million milestone payment upon achievement of a specified clinical development milestone event, (ii) up to $70.0 million in milestone payments upon achievement of specified regulatory milestone events, and (iii) a $25.0 million milestone payment upon achievement of a specified commercial milestone event. The Company is also eligible to receive additional milestone payments specific to co-commercialized licensed programs and split licensed programs. In addition, the Company is eligible to receive a substantive milestone payment of $22.5 million upon achievement of an early clinical development milestone event for certain co-commercialized licensed programs. In connection with the first split licensed program under the collaboration, the Company’s IDH1 program, AG-120, the Company is eligible to receive an additional one-time payment of $25.0 million upon the dosing of the last patient in a Company-sponsored phase 2 clinical trial.

In addition to the milestone payments described above, for each co-commercialized licensed program, the Company will be reimbursed for all eligible development costs of the related phase 1 multiple ascending dose (MAD) study. The initial costs will be reimbursed as a milestone payment equal to the greater of $5.0 million or eligible development costs incurred by the Company upon the earlier of the determination of the maximum tolerated dose (MTD) or Celgene’s election to license the program. Subsequent to the initial milestone payment, development costs will be reimbursed on a quarterly basis. As of September 30, 2014, the Company has recorded a collaboration receivable of $18.7 million related to reimbursable development costs for AG-221, which includes the initial milestone.

In addition to the milestone payments described above, for each split licensed program, the Company is eligible for reimbursement of the costs of disease-specific expansion cohort(s) that support the initiation of a subsequent pivotal clinical trial. Costs will be reimbursed as a milestone payment equal to the lesser of $10.0 million or fifty percent of the eligible costs for the disease-specific expansion cohort(s) upon the first patient dosed under the pivotal clinical trial. The maximum amount for the milestone payment will be $10.0 million for each split program regardless of the number of disease-specific expansion cohorts and pivotal trials undertaken for each split program.

The Company has concluded that certain of the clinical development and regulatory milestones that may be received under the Celgene agreement, if the Company is involved in future product development and commercialization, are substantive. Factors considered in the evaluation of the milestones included the degree of risk associated with performance of the milestone, the level of effort and investment required, whether the milestone consideration was reasonable relative to the deliverables and whether the milestone was earned at least in part based on the Company’s performance. Revenues from substantive milestones, if they are nonrefundable, are recognized as revenue upon successful accomplishment of the milestones. Clinical and regulatory milestones are deemed non-substantive if they are based solely on the collaborator’s performance. Non-substantive milestones will be recognized when achieved to the extent the Company has no remaining performance obligations under the arrangement. Milestone payments earned upon achievement of commercial milestone events will be recognized when earned.

The Company may also receive royalties at tiered, low- to mid-teen percentage rates on net sales and has the option to participate in the development and commercialization of certain products in the United States. The royalty payments are recognized as revenue in the period in which they are earned. No other milestone or royalty payments under the agreement have been earned.

Accrued_Expenses_and_Other_Cur

Accrued Expenses and Other Current Liabilities	9 Months Ended
Accrued Expenses and Other Current Liabilities	Sep. 30, 2014
Payables and Accruals [Abstract]	'
Accrued Expenses and Other Current Liabilities	'
	6. Accrued Expenses and Other Current Liabilities
	Accrued expenses and other current liabilities consist of the following (in thousands):


		September 30,		December 31,
		2014		2013
	Accrued compensation	$	3,273	$	3,642
	Accrued contracted research and development costs		4,425		2,484
	Accrued professional fees		1,271		320
	Accrued other		1,035		140

	Total	$	10,004	$	6,586

ShareBased_Payments

Share-Based Payments	9 Months Ended
Share-Based Payments	Sep. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Share-Based Payments	'

	7. Share-Based Payments

	2013 Stock Incentive Plan

	In June 2013, the Company’s Board of Directors adopted, and in July 2013, the Company’s stockholders approved, the 2013 Stock Incentive Plan (the “2013 Plan”). The 2013 Plan became effective upon the closing of the IPO and provides for the grant of incentive stock options, non-qualified stock options, stock appreciation rights, restricted stock awards, restricted stock units and other stock-based awards. As of September 30, 2014, the total number of shares reserved under all equity plans is 4,616,104 and the Company had 799,270 shares available for future issuance under such plans. The 2013 Plan provides for an annual increase, to be added on the first day of each fiscal year, beginning with the fiscal year ending December 31, 2014 and continuing until the expiration of the 2013 Plan, equal to the lesser of (i) 2,000,000 shares of Common Stock, (ii) 4% of the outstanding shares of Common Stock on such date or (iii) an amount determined by the Company’s Board of Directors. On January 1, 2014, the annual increase for the 2013 Plan resulted in an additional 1,242,966 shares authorized for issuance.

	The following table summarizes the activity of all stock incentive plans for the nine months ended September 30, 2014:



			Number of				Weighted-			Weighted-			Aggregate
			Stock Options				Average			Average			Intrinsic
							Exercise			Remaining			Value
							Price			Contractual			(in thousands)
										Term
										(in years)
	Outstanding at December 31, 2013			3,846,168			$	4.14			7.43		$	76,189
	Granted			1,176,733				33.23
	Exercised			(1,128,065	)			1.42
	Forfeited/cancelled			(78,002	)			12.75

	Outstanding at September 30, 2014			3,816,834			$	13.74			7.7		$	181,726

	Exercisable at September 30, 2014			1,635,445			$	2.02			6.01		$	97,023

	Vested and expected to vest at September 30, 2014			3,373,444			$	13.67			7.57		$	160,838


	The weighted-average grant date fair value of options granted was $31.14, $16.30, $24.30 and $9.83 during the three months ended September 30, 2014 and 2013 and the nine months ended September 30, 2014 and 2013, respectively. The total intrinsic value of options exercised was $10 million, $0.2 million, $44.8 million, and $0.6 million during the three months ended September 30, 2014 and 2013 and the nine months ended September 30, 2014 and 2013, respectively.

	At September 30, 2014, the total unrecognized compensation expense related to unvested stock option awards, including estimated forfeitures, was $27.4 million, which the Company expects to recognize over a weighted-average period of approximately 3.1 years. The Company also has unrecognized stock-based compensation expense of $2.8 million related to stock options with performance-based vesting criteria that are not considered probable of achievement as of September 30, 2014; therefore the Company has not yet begun to recognize the expense on these awards.

	Restricted Stock Units

	The Company may grant awards of restricted stock units (“RSUs”) to non-employee directors, members of the management team and employees on a discretionary basis pursuant to the 2013 Plan. Each RSU entitles the holder to receive, at the end of each vesting period, a specified number of shares of the Company’s common stock. The total number of unvested RSUs at September 30, 2014 was 10,000. The issued and outstanding RSUs vest on the first anniversary of the grant date.



	The fair value of the RSUs granted in the three and nine months ended September 30, 2014 was approximately $0.5 million. No RSUs were granted in the three and nine months ended September 30, 2013. The Company recorded stock-based compensation expense related to RSUs of $0.1 million for the three and nine months ended September 30, 2014. No compensation expense related to RSUs was recorded during 2013. These amounts are included in the total stock-based compensation expense disclosed below. As of September 30, 2014, there was approximately $0.5 million of total unrecognized compensation expense related to RSUs, which is expected to be recognized over a period of one year.

	The following table presents unvested RSU activity for the nine months ended September 30, 2014:



			Nine Months Ended
			September 30, 2014
	Unvested shares beginning of period			—
	Granted			10,000
	Vested			—

	Unvested shares end of period			10,000


	Restricted Stock

	At September 30, 2014, there were 11,363 shares of unvested restricted stock which remain subject to the Company’s right of repurchase.

	Unvested restricted stock activity for the nine months ended September 30, 2014 is summarized as follows:



			Nine Months Ended
September 30, 2014
Unvested shares beginning of period				23,295
Vested			(11,932	)

Unvested shares end of period			11,363


Performance-Based Stock Option Grants

During the nine months ended September 30, 2014, no options to purchase shares of common stock were granted which contain performance-based or a combination of performance-based and service-based vesting criteria. During the nine months ended September 30, 2013, the Company granted 355,454 shares of common stock, which contain performance-based and service-based vesting criteria, to employees. Performance-based vesting criteria for these options primarily relate to milestone events specific to the Company’s corporate goals, including but not limited to certain preclinical and clinical development milestones related to the Company’s product candidates. Stock-based compensation expense associated with these performance-based stock options is recognized if the performance condition is considered probable of achievement using management’s best estimates. As of September 30, 2014, certain of the performance-based milestones had been achieved and therefore the related expense has either been fully recognized or is being recognized over the remaining service period. The achievement of the remaining milestones was deemed to be not probable as of September 30, 2014 and therefore no expense has been recognized related to these awards. During the three months ended September 2014 and 2013 and nine months ended September 2014 and 2013, the Company recognized stock-based compensation expense of $0.1 million, $0.1 million, $0.1 million, and $0.3 million, respectively, related to stock options with performance-based vesting criteria.



Stock-Based Compensation Expense

During the three and nine months ended September 30, 2014 and 2013, the Company recorded stock-based compensation expense for employee and non-employee stock options, restricted stock units and restricted stock, which was allocated as follows in the condensed consolidated interim statements of operations (in thousands):



		Three Months Ended September 30,							Nine Months Ended September 30,
		2014				2013			2014			2013
Research and development expense		$	1,438			$	919		$	3,899		$	1,452
General and administrative expense			1,428				193			2,853			413

		$	2,866			$	1,112		$	6,752		$	1,865


The fair value of each stock option granted to employees is estimated on the date of grant using the Black-Scholes option-pricing model. For non-employees, the fair value of each stock option is estimated on each vesting and reporting date using the Black-Scholes option-pricing model. The following table summarizes the weighted average assumptions used in calculating the grant date fair value of the awards:



		Three Months Ended September 30,							Nine Months Ended September 30,
		2014				2013			2014			2013
Risk-free interest rate			1.95	%			1.73	%		1.83	%		1.23	%
Expected dividend yield			—				—			—			—
Expected term (in years)			6				6.09			6.02			6.36
Expected volatility			78.89	%			94.25	%		84. 77	%		92.6	%

2013 Employee stock purchase plan

In June 2013, the Company’s Board of Directors adopted, and in July 2013 the Company’s stockholders approved, the 2013 Employee Stock Purchase Plan (the “2013 ESPP”). The 2013 ESPP will be administered by the Company’s Board of Directors or by a committee appointed by the Company’s Board of Directors. Under the 2013 ESPP, each offering period is six months, at the end of which employees may purchase shares of common stock through payroll deductions made over the term of the offering period. The per-share purchase price at the end of each offering period is equal to 85% of the closing price of one share of the Company’s common stock at the beginning or end of the offering period, whichever is lower, subject to Internal Revenue Service limits. The Company’s first offering period was initiated on September 1, 2014. No shares were issued for the three and nine months ended September 30, 2014 under the 2013 ESPP. The 2013 ESPP initially provides participating employees with the opportunity to purchase up to an aggregate of 327,272 shares of the Company’s common stock.

The Company recorded less than $0.1 million of stock-based compensation expense for the three months ended September 30, 2014 related to the 2013 ESPP. No stock-based compensation expense related to the 2013 ESPP was recorded during 2013.

Income_Taxes

Income Taxes	9 Months Ended
Income Taxes	Sep. 30, 2014
Income Tax Disclosure [Abstract]	'
Income Taxes	'

	8. Income Taxes

	The (benefit) provision for income taxes is as follows for the three and nine months ended September 30, 2014 and 2013 (in thousands):



		Three Months Ended September 30,					Nine Months Ended September 30,
		2014			2013		2014			2013
	Current:
	Federal	$	(448	)	$	121	$	(448	)	$	410
	State		—			—		—			—

	Total current		(448	)		121		(448	)		410
	Deferred:
	Federal		—			—		—			—
	State		—			—		—			—

	Total deferred		—			—		—			—

	Total	$	(448	)	$	121	$	(448	)	$	410


	As required by ASC 740, Income Taxes (“ASC 740”), management of the Company has evaluated the positive and negative evidence bearing upon the realizability of the Company’s deferred tax assets, which are comprised principally of timing differences related to the recognition of revenue under the Celgene Agreement for financial statement versus tax purposes. During the year ended December 31, 2011, management determined that it was more likely than not that it would realize a portion of its deferred tax assets because of the Company’s ability to carryback future losses for U.S. federal income tax purposes. As a result, the Company reversed approximately $10.7 million of the valuation allowance on its deferred tax assets in the year ended December 31, 2011, representing the amount of deferred tax assets that would be realized in 2012 and 2013, the years available for carryback. The Company utilized certain of the deferred tax assets, including net operating losses, generated in the years ended December 31, 2013 and 2012 to reduce its federal income taxes payable each year. The provision for income taxes for the three and nine months ended September 30, 2013 was attributable to penalties and interest accrued for the non-payment of U.S. federal income taxes.

	In January 2014, the Company paid $6.0 million as payment in full of its U.S. federal income tax liability related to the year ended December 31, 2011, including $1.5 million of interest and penalties accrued. The Company has filed a carryback claim to apply the net losses incurred during the year ended December 31, 2013 against the previous taxable income and expects to receive a refund of $3.8 million of the amounts paid in January 2014 after the filing of the Company’s 2013 tax return which occurred in September 2014. The amount expected to be refunded by the Internal Revenue Service (“IRS”) is recorded as refundable income taxes as of September 30, 2014. The Company received abatements from the IRS of $1.1 million related to penalties previously paid by the Company of which $0.7 million was received in June 2014 and $0.4 million was received during the three months ended September 30, 2014. The $0.7 million abatement was known as of December 31, 2013 and was recorded as a benefit in the 2013 tax provision. The Company did not receive notification of the $0.4 million abatement until August 2014. Accordingly, this abatement is reflected in the income tax benefit for the three months ended September 30, 2014.

	The Company applies the accounting guidance in ASC 740 related to accounting for uncertainty in income taxes. The Company’s reserves related to taxes are based on a determination of whether, and how much of, a tax benefit taken by the Company in its tax filings or positions is more likely than not to be realized following resolution of any potential contingencies present related to the tax benefit. As of September 30, 2014, the Company had no unrecognized tax benefits. The Company recognizes interest and penalties related to uncertain tax positions in the (benefit) provision for income taxes.

Earnings_per_Share_Applicable_

Earnings per Share Applicable to Common Stockholders	9 Months Ended
Earnings per Share Applicable to Common Stockholders	Sep. 30, 2014
Earnings Per Share [Abstract]	'
Earnings per Share Applicable to Common Stockholders	'
	9. Earnings per Share Applicable to Common Stockholders
	Basic net income (loss) per share applicable to common stockholders is calculated by dividing net income (loss) applicable to common stockholders by the weighted-average shares outstanding during the period, without consideration for common stock equivalents. Net income (loss) applicable to common stockholders is calculated by adjusting the net income (loss) of the Company for cumulative preferred stock dividends for periods when preferred stock was outstanding.
	Diluted net income per share applicable to common stockholders is calculated by adjusting weighted-average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury-stock method. For purposes of calculating diluted net loss per share applicable to common stockholders, common stock equivalents outstanding for the period are excluded, as their effect would be anti-dilutive.
	The following table shows the calculation of basic and diluted earnings per share for the three and nine month periods ended September 30, 2014 and September 30, 2013 (in thousands, except share and per share data):


		Three Months Ended September 30,					Nine Months Ended September 30,
		2014		2013			2014			2013
	Net income (loss) applicable to common stockholders		3,704		(11,744	)		(26,840	)		(31,187	)
	Weighted-average shares:
	Basic		34,495,076		22,744,486			33,176,801			10,111,735
	Effect of dilutive securities:
	Stock options and restricted stock units		2,085,068		—			—			—
	Unvested restricted stock		12,523		—			—			—
	Employee stock purchase plan options		16		—			—			—

	Diluted		36,592,683		22,744,486			33,176,801			10,111,735

	Net income (loss) per share:
	Basic		0.11		(0.52	)		(0.81	)		(3.08	)
	Diluted		0.1		(0.52	)		(0.81	)		(3.08	)
	The following potentially dilutive securities were excluded from the calculation of diluted net income (loss) per share applicable to common stockholders for the periods indicated because their effect would have been anti-dilutive:


		Three Months Ended September 30,					Nine Months Ended September 30,
		2014		2013			2014			2013
	Stock options and restricted stock units		1,484,917		3,905,932			3,816,834			3,905,932
	Unvested restricted stock		—		36,568			11,363			36,568
	Employee stock purchase plan options		—		—			1,764			—

			1,484,917		3,942,500			3,829,961			3,942,500

Commitments_and_Contingencies

Commitments and Contingencies	9 Months Ended
Commitments and Contingencies	Sep. 30, 2014
Commitments and Contingencies Disclosure [Abstract]	'
Commitments and Contingencies	'

	10. Commitments and Contingencies

	Operating Lease

	On September 15, 2014, the Company entered into an operating lease agreement (the “Lease”) for 74,498 square feet of office and laboratory space located at 88 Sidney Street, Cambridge, Massachusetts. The Company also entered into an agreement to terminate its existing lease under which the Company currently leases 38,536 square feet of office and laboratory space located at 38 Sidney Street, Cambridge, Massachusetts. The Company’s existing lease will terminate thirty days after the Commencement Date. The date on which the Company will become responsible for paying rent under the Lease (the “Commencement Date”) will be the earlier of May 15, 2015 or the date upon which the Company first begins conducting business at the new location. The Company’s existing lease will terminate thirty days after the Commencement Date. The initial lease term will be for a period of seven years from the Commencement Date. At the end of the lease term, the Company has the option to extend the Lease for two consecutive terms of five years at fair market rent at the time of the extension. The Lease agreement includes rent escalation clauses, a tenant improvement allowance of $11.2 million and access to temporary space located at the premises for no cost. The Company gained physical access to the leased space in September 2014 and began to record rent expense on a straight-line basis over the effective term of the Lease. The Company provided a standby letter of credit of $1.4 million as security for its obligations under the Lease which was issued in October 2014.

	Future annual minimum lease payments due under the new and existing operating leases at December 31 of each year are as follows (in thousands):



	2014	$	677
	2015		3,538
	2016		4,318
	2017		4,405
	2018		4,493
	Thereafter		15,826

		$	33,257


	Rent expense was $0.7 million and $0.5 million for the three months ended September 30, 2014 and 2013, respectively and was $1.8 million and $1.6 million for the nine months ended September 30, 2014 and 2013, respectively. The operating leases require the Company to share in prorated operating expenses and property taxes based upon actual amounts incurred; those amounts are not fixed for future periods and, therefore, are not included in the future commitments listed above.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Policies)	9 Months Ended
	Sep. 30, 2014
Accounting Policies [Abstract]	'
Multiple-Element Revenue Arrangements	'

	In July 2014, the Company amended its collaboration agreement with Celgene. As a result of the amendment, the Company was required to reevaluate the agreement under Financial Accounting Standards Board (“FASB”) Accounting Standards Update (“ASU”) No. 2009-13, Multiple-Element Revenue Arrangements (“ASU No. 2009-13”). The amendment was determined to be a material modification pursuant to ASU No. 2009-13, and the Company will recognize revenue for the arrangement under this guidance on a prospective basis, as discussed in Note 5.
ASU 2014-15, Presentation of Financial Statements - Going Concern (Subtopic 205-40)	'

	In August 2014, the FASB issued ASU No. 2014-15, Presentation of Financial Statements—Going Concern (Subtopic 205-40). The ASU requires all entities to evaluate for the existence of conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the issuance date of the financial statements. The accounting standard is effective for interim and annual periods ending after December 15, 2016, and will not have a material impact on the consolidated financial statements, but may impact the Company’s footnote disclosures.
ASU 2014-12, Compensation-Stock Compensation (Topic 718)	'

	In June 2014, the FASB issued ASU No. 2014-12, Compensation—Stock Compensation (Topic 718). The ASU clarifies how entities should treat performance targets that can be achieved after the requisite service period of a share-based payment award. The accounting standard is effective for interim and annual periods beginning after December 15, 2015 and is not expected to have a material impact on the consolidated financial statements.
ASU 2014-09, Revenue from Contracts with Customers (Topic 606)	'

	In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606). The ASU provides for a single comprehensive model for use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance. The accounting standard is effective for interim and annual periods beginning after December 15, 2016 with no early adoption permitted. The Company is required to adopt the amendments in the ASU using one of two acceptable methods. The Company is currently in the process of determining which adoption method it will apply evaluating the impact of the guidance on its consolidated financial statements.
Recent Accounting Pronouncements	'

	Other accounting standards that have been issued by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on the Company’s financial statements upon adoption.
Fair Value Measurements and Disclosures	'
	The Company records cash equivalents and marketable securities at fair value. Accounting Standards Codification (“ASC”) Topic 820, Fair Value Measurements and Disclosures, established a fair value hierarchy for those instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and the Company’s own assumptions (unobservable inputs). The hierarchy consists of three levels:
	Level 1 – Unadjusted quoted prices in active markets for identical assets or liabilities.
	Level 2 – Quoted prices for similar assets and liabilities in active markets, quoted prices in markets that are not active, or inputs which are observable, either directly or indirectly, for substantially the full term of the asset or liability.
	Level 3 – Unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability in which there is little, if any, market activity for the asset or liability at the measurement date.
Investments - Debt and Equity Securities	'

	Marketable securities at September 30, 2014 and December 31, 2013 consisted primarily of investments in United States Treasuries and certificates of deposit. Management determines the appropriate classification of the securities at the time they are acquired and evaluates the appropriateness of such classifications at each balance sheet date. The Company classifies its marketable securities as available-for-sale pursuant to ASC 320, Investments – Debt and Equity Securities. Marketable securities are recorded at fair value, with unrealized gains and losses included as a component of accumulated other comprehensive income in stockholders’ equity and a component of total comprehensive income (loss) in the condensed consolidated interim statements of comprehensive income (loss), until realized. Realized gains and losses are included in investment income on a specific-identification basis. There were no realized gains or losses on marketable securities for the three or nine months ended September 30, 2014 and 2013.

	The Company reviews marketable securities for other-than-temporary impairment whenever the fair value of a marketable security is less than the amortized cost and evidence indicates that a marketable security’s carrying amount is not recoverable within a reasonable period of time. Other-than-temporary impairments of investments are recognized in the condensed consolidated interim statements of operations if the Company has experienced a credit loss, has the intent to sell the marketable security, or if it is more likely than not that the Company will be required to sell the marketable security before recovery of the amortized cost basis. Evidence considered in this assessment includes reasons for the impairment, compliance with the Company’s investment policy, the severity and the duration of the impairment and changes in value subsequent to the end of the period.

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	9 Months Ended
Fair Value Measurements (Tables)	Sep. 30, 2014
Fair Value Disclosures [Abstract]	'
Cash Equivalents and Marketable Securities Measured at Fair Value on a Recurring Basis	'

	The following table summarizes the cash equivalents and marketable securities measured at fair value on a recurring basis as of September 30, 2014 (in thousands):



		Level 1		Level 2		Level 3		Total
	Cash equivalents	$	69,245	$	480	$	—	$	69,725
	Marketable securities:
	Certificates of deposit		—		14,521		—		14,521
	U.S. Treasuries		153,317		—		—		153,317

		$	222,562	$	15,001	$	—	$	237,563




	The following table summarizes the cash equivalents and marketable securities measured at fair value on a recurring basis as of December 31, 2013 (in thousands):



		Level 1		Level 2		Level 3		Total
	Cash equivalents	$	68,792	$	—	$	—	$	68,792
	Marketable securities:
	Certificates of deposit		—		6,915		—		6,915
	U.S. Treasuries		115,419		—		—		115,419

		$	184,211	$	6,915	$	—	$	191,126

Marketable_Securities_Tables

Marketable Securities (Tables)	9 Months Ended
Marketable Securities (Tables)	Sep. 30, 2014
Investments, Debt and Equity Securities [Abstract]	'
Marketable Securities	'

	Marketable securities at September 30, 2014 consist of the following (in thousands):



		Amortized Cost		Unrealized		Unrealized			Fair
		Amortized Cost		Gains		Losses			Value
	Current:
	Certificates of deposit	$	14,530	$	—	$	(9	)	$	14,521
	U.S. Treasuries		135,348		53		(1	)		135,400
	Non-current:
	U.S. Treasuries		17,909		8		—			17,917

		$	167,787	$	61	$	(10	)	$	167,838




	Marketable securities at December 31, 2013 consist of the following (in thousands):



		Amortized Cost		Unrealized		Unrealized			Fair
		Amortized Cost		Gains		Losses			Value
	Current:
	Certificates of deposit	$	6,920	$	—	$	(5	)	$	6,915
	U.S. Treasuries		88,287		8		(1	)		88,294
	Non-current:
	U.S. Treasuries		27,113		12		—			27,125

		$	122,320	$	20	$	(6	)	$	122,334

Accrued_Expenses_and_Other_Cur1

Accrued Expenses and Other Current Liabilities (Tables)	9 Months Ended
Accrued Expenses and Other Current Liabilities (Tables)	Sep. 30, 2014
Payables and Accruals [Abstract]	'
Summary of Accrued Expenses and Other Current Liabilities	'
	Accrued expenses and other current liabilities consist of the following (in thousands):


		September 30,		December 31,
		2014		2013
	Accrued compensation	$	3,273	$	3,642
	Accrued contracted research and development costs		4,425		2,484
	Accrued professional fees		1,271		320
	Accrued other		1,035		140

	Total	$	10,004	$	6,586

ShareBased_Payments_Tables

Share-Based Payments (Tables)	9 Months Ended
Share-Based Payments (Tables)	Sep. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Summary of Activity of All Stock Incentive Plans	'
	The following table summarizes the activity of all stock incentive plans for the nine months ended September 30, 2014:


		Number of			Weighted-			Weighted-			Aggregate
		Stock Options			Average			Average			Intrinsic
					Exercise			Remaining			Value
					Price			Contractual			(in thousands)
								Term
								(in years)
	Outstanding at December 31, 2013		3,846,168		$	4.14			7.43		$	76,189
	Granted		1,176,733			33.23
	Exercised		(1,128,065	)		1.42
	Forfeited/cancelled		(78,002	)		12.75

	Outstanding at September 30, 2014		3,816,834		$	13.74			7.7		$	181,726

	Exercisable at September 30, 2014		1,635,445		$	2.02			6.01		$	97,023

	Vested and expected to vest at September 30, 2014		3,373,444		$	13.67			7.57		$	160,838

Unvested Stock Unit Activity	'

	The following table presents unvested RSU activity for the nine months ended September 30, 2014:



		Nine Months Ended
		September 30, 2014
	Unvested shares beginning of period		—
	Granted		10,000
	Vested		—

	Unvested shares end of period		10,000

Unvested Stock Unit Activity	'
	Unvested restricted stock activity for the nine months ended September 30, 2014 is summarized as follows:


		Nine Months Ended
		September 30, 2014
	Unvested shares beginning of period		23,295
	Vested		(11,932	)

	Unvested shares end of period		11,363

Recorded Stock-Based Compensation Expense for Employee and Non-Employee Stock Options, Restricted Stock Units and Restricted Stock	'

	During the three and nine months ended September 30, 2014 and 2013, the Company recorded stock-based compensation expense for employee and non-employee stock options, restricted stock units and restricted stock, which was allocated as follows in the condensed consolidated interim statements of operations (in thousands):



		Three Months Ended September 30,						Nine Months Ended September 30,
		2014			2013			2014			2013
	Research and development expense	$	1,438		$	919		$	3,899		$	1,452
	General and administrative expense		1,428			193			2,853			413

		$	2,866		$	1,112		$	6,752		$	1,865

Schedule of Grant Date Fair Value Option Award Weighted Average Assumptions Used	'

	The following table summarizes the weighted average assumptions used in calculating the grant date fair value of the awards:



		Three Months Ended September 30,						Nine Months Ended September 30,
		2014			2013			2014			2013
	Risk-free interest rate		1.95	%		1.73	%		1.83	%		1.23	%
	Expected dividend yield		—			—			—			—
	Expected term (in years)		6			6.09			6.02			6.36
	Expected volatility		78.89	%		94.25	%		84. 77	%		92.6	%

Income_Taxes_Tables

Income Taxes (Tables)	9 Months Ended
Income Taxes (Tables)	Sep. 30, 2014
Income Tax Disclosure [Abstract]	'
Benefit (Provision) for Income Taxes	'

	The (benefit) provision for income taxes is as follows for the three and nine months ended September 30, 2014 and 2013 (in thousands):



		Three Months Ended September 30,					Nine Months Ended September 30,
		2014			2013		2014			2013
	Current:
	Federal	$	(448	)	$	121	$	(448	)	$	410
	State		—			—		—			—

	Total current		(448	)		121		(448	)		410
	Deferred:
	Federal		—			—		—			—
	State		—			—		—			—

	Total deferred		—			—		—			—

	Total	$	(448	)	$	121	$	(448	)	$	410

Earnings_per_Share_Applicable_1

Earnings per Share Applicable to Common Stockholders (Tables)	9 Months Ended
	Sep. 30, 2014
Earnings Per Share [Abstract]	'
Calculation of Basic and Diluted Earnings Per Share	'
	The following table shows the calculation of basic and diluted earnings per share for the three and nine month periods ended September 30, 2014 and September 30, 2013 (in thousands, except share and per share data):


		Three Months Ended September 30,					Nine Months Ended September 30,
		2014		2013			2014			2013
	Net income (loss) applicable to common stockholders		3,704		(11,744	)		(26,840	)		(31,187	)
	Weighted-average shares:
	Basic		34,495,076		22,744,486			33,176,801			10,111,735
	Effect of dilutive securities:
	Stock options and restricted stock units		2,085,068		—			—			—
	Unvested restricted stock		12,523		—			—			—
	Employee stock purchase plan options		16		—			—			—

	Diluted		36,592,683		22,744,486			33,176,801			10,111,735

	Net income (loss) per share:
	Basic		0.11		(0.52	)		(0.81	)		(3.08	)
	Diluted		0.1		(0.52	)		(0.81	)		(3.08	)
Common Stock Excluded from Calculation of Diluted Earnings Per Share	'
	The following potentially dilutive securities were excluded from the calculation of diluted net income (loss) per share applicable to common stockholders for the periods indicated because their effect would have been anti-dilutive:


		Three Months Ended September 30,					Nine Months Ended September 30,
		2014		2013			2014			2013
	Stock options and restricted stock units		1,484,917		3,905,932			3,816,834			3,905,932
	Unvested restricted stock		—		36,568			11,363			36,568
	Employee stock purchase plan options		—		—			1,764			—

			1,484,917		3,942,500			3,829,961			3,942,500

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	9 Months Ended
Commitments and Contingencies (Tables)	Sep. 30, 2014
Commitments and Contingencies Disclosure [Abstract]	'
Summary of Future Annual Minimum Lease Payments Due Under Operating Lease	'

	Future annual minimum lease payments due under the new and existing operating leases at December 31 of each year are as follows (in thousands):



	2014	$	677
	2015		3,538
	2016		4,318
	2017		4,405
	2018		4,493
	Thereafter		15,826

		$	33,257

Overview_and_Basis_of_Presenta1

Overview and Basis of Presentation - Additional Information (Detail) (USD $)	0 Months Ended	9 Months Ended		0 Months Ended	1 Months Ended	0 Months Ended	1 Months Ended	0 Months Ended	1 Months Ended	0 Months Ended	1 Months Ended
In Millions, except Share data, unless otherwise specified	Jul. 29, 2013	Sep. 30, 2014	Sep. 30, 2014	Jul. 29, 2013	Apr. 30, 2014	Jul. 29, 2013	31-May-14	Jul. 29, 2013	Apr. 30, 2014	Jul. 29, 2013	31-May-14
			Minimum [Member]	IPO [Member]	IPO [Member]	Underwriter [Member]	Underwriter [Member]	Private Placement [Member]	Private Placement [Member]	Private Placement [Member]	Private Placement [Member]
			Diseases							Celgene [Member]	Celgene [Member]
Basis Of Presentation [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Number of rare genetic disease under entity therapeutic group	'	'	600	'	'	'	'	'	'	'	'
Common stock shares purchased	'	'	'	6,772,221	2,000,000	883,333	300,000	708,333	294,800	'	'
Public offering price	'	'	'	$18	$44	'	'	$18	'	'	'
Net proceeds from the IPO	'	'	'	$111	$82.30	'	'	'	'	$12.80	$12.40
Reverse stock split	'	'1-for-2.75	'	'	'	'	'	'	'	'	'
Reverse stock split ratio	'	0.3636	'	'	'	'	'	'	'	'	'
Additional outstanding shares common stock	19,731,564	'	'	'	'	'	'	'	'	'	'

Fair_Value_Measurements_Cash_E

Fair Value Measurements - Cash Equivalents and Marketable Securities Measured at Fair Value on a Recurring Basis (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Marketable securities	$167,838	$122,334
Fair Value, Measurements, Recurring [Member]	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Cash equivalents	69,725	68,792
Cash equivalents and marketable securities, total	237,563	191,126
Fair Value, Measurements, Recurring [Member] \| Certificates of Deposit [Member]	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Marketable securities	14,521	6,915
Fair Value, Measurements, Recurring [Member] \| U.S. Treasuries [Member]	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Marketable securities	153,317	115,419
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Cash equivalents	69,245	68,792
Cash equivalents and marketable securities, total	222,562	184,211
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member] \| U.S. Treasuries [Member]	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Marketable securities	153,317	115,419
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Cash equivalents	480	'
Cash equivalents and marketable securities, total	15,001	6,915
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member] \| Certificates of Deposit [Member]	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Marketable securities	$14,521	$6,915

Fair_Value_Measurements_Additi

Fair Value Measurements - Additional Information (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'	'
Financial assets or liabilities that were classified as Level 3	$0	'	$0
Transfers of assets from Level 1 to Level 2	0	0	'
Transfers of assets from Level 2 to Level 1	0	0	'
Transfers of liabilities from Level 1 to Level 2	0	0	'
Transfers of liabilities from Level 2 to Level 1	0	0	'
Level 3 [Member]	'	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'	'
Financial assets classified as Level 3	0	0	'
Financial liabilities classified as Level 3	$0	$0	'

Marketable_Securities_Addition

Marketable Securities - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended			9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014	Dec. 31, 2013
	Securities	Sep. 30, 2013	Securities	Sep. 30, 2013	Securities	Maximum [Member]	Maximum [Member]	Minimum [Member]	Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]	'	'	'	'	'	'	'	'	'
Realized gains or losses on marketable securities	$0	$0	$0	$0	'	'	'	'	'
Investment maturity period, non-current	'	'	'	'	'	'2 years	'2 years	'1 year	'1 year
Investment maturity period, current	'	'	'	'	'	'1 year	'1 year	'	'
Debt securities in an unrealized loss position	60	'	60	'	33	'	'	'	'
Aggregate fair value of debt securities in an unrealized loss position	$21,500,000	'	$21,500,000	'	$31,700,000	'	'	'	'
Securities in significant unrealized loss position	0	'	0	'	0	'	'	'	'

Marketable_Securities_Marketab

Marketable Securities - Marketable Securities (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized Cost	$167,787	$122,320
Unrealized Gains	61	20
Unrealized Losses	-10	-6
Fair Value	167,838	122,334
Current: [Member] \| Certificates of Deposit [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized Cost	14,530	6,920
Unrealized Losses	-9	-5
Fair Value	14,521	6,915
Current: [Member] \| U.S. Treasuries [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized Cost	135,348	88,287
Unrealized Gains	53	8
Unrealized Losses	-1	-1
Fair Value	135,400	88,294
Non-Current: [Member] \| U.S. Treasuries [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized Cost	17,909	27,113
Unrealized Gains	8	12
Fair Value	$17,917	$27,125

Collaboration_Agreements_Addit

Collaboration Agreements - Additional Information (Detail) (USD $)

0 Months Ended

1 Months Ended

9 Months Ended

12 Months Ended

1 Months Ended

3 Months Ended

9 Months Ended

0 Months Ended

1 Months Ended

9 Months Ended

1 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

1 Months Ended

9 Months Ended

Jul. 29, 2013

31-May-14

Dec. 31, 2013

Oct. 31, 2011

Apr. 30, 2010

Sep. 30, 2014

Dec. 31, 2013

Jul. 31, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Jul. 31, 2014

Jan. 01, 2014

Jul. 31, 2014

Sep. 30, 2014

Jul. 31, 2014

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Jul. 31, 2013

Sep. 30, 2014

Licensed_Program

Celgene [Member]

Maximum [Member]

Minimum [Member]

Series B Convertible Preferred Stock [Member]

Candidate

Split License [Member]

In Process Research and Development [Member]

Participation Service [Member]

MTD [Member]

Before Amendment [Member]

Celgene [Member]

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Agreement amended date

'2011-10

Amended collaboration expiration date

'2015-04

'2014-04

'2015-04

Discovery phase years

'2 years

Term of the initial discovery period before amendment to extend

'4 years

'3 years

'4 years

Term of extended period after amendment of the initial discovery period

'5 years

'4 years

'5 years

Eligible payment to be received from extension of the discovery phase

$20,000,000

Date of extension of discovery phase

'2016-04

Number of candidates confirmed by the Joint Research Committee

Number of licensed programs type under collaboration agreements

Period considered for agreement termination notice

'30 days

Upfront payment received

121,200,000

Series B convertible preferred stock, purchased

5,190,551

Series B convertible preferred stock price per share

$1.70

Net proceeds of Series B convertible preferred stock

8,800,000

Additional consideration under agreement

3,100,000

Series B convertible preferred stock at fair value

5,700,000

Reverse stock split

'1-for-2.75

Reverse stock split ratio

0.3636

Additional outstanding shares common stock

19,731,564

1,887,473

Payment made in pursuant to the amendment

20,000,000

Milestone payment upon achievement of a specified clinical development milestone event

10,000,000

25,000,000

10,000,000

Milestone payment reimbursement, percentage

50.00%

Number of years company expected to fulfill its performance obligations

'6 years

Revenue recognition, selling price

21,200,000

42,700,000

13,600,000

50,800,000

200,000

Revenue recognized during period

8,000,000

Collaboration revenue

6,300,000

18,800,000

50,700,000

33,900,000

Receipts of potential milestone payments

120,000,000

Milestone payments upon achievement of specified regulatory milestone events

70,000,000

Milestone payment upon achievement of a specified commercial milestone event

25,000,000

Achievement of an early clinical development milestone event

22,500,000

Dosing of the last patient in a Company-sponsored

25,000,000

Received amount of development cost

5,000,000

Collaboration receivable

18,700,000

Milestone or royalty payments received

Accrued_Expenses_and_Other_Cur2

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Payables and Accruals [Abstract]	'	'
Accrued compensation	$3,273	$3,642
Accrued contracted research and development costs	4,425	2,484
Accrued professional fees	1,271	320
Accrued other	1,035	140
Total	$10,004	$6,586

ShareBased_Payments_Additional

Share-Based Payments - Additional Information (Detail) (USD $)

3 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

0 Months Ended

6 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Dec. 31, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Dec. 31, 2013

Jan. 01, 2014

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Performance-Based Stock Option Grants [Member]

Restricted Stock [Member]

2013 Stock Incentive Plan [Member]

2013 Employee Stock Purchase Plan [Member]

Maximum [Member]

Performance-Based Stock Option Grants [Member]

Stock Option Grant [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Common stock reserved for issuance

4,616,104

Shares available for future issuance

799,270

Common stock

2,000,000

Common stock outstanding

4.00%

Shares authorized for issuance

1,242,966

Weighted-average grant date fair value of options

$31.14

$16.30

$24.30

$9.83

Intrinsic value of options exercised

$10,000,000

$200,000

$44,800,000

$600,000

Unrecognized compensation expense related to stock option

500,000

27,400,000

2,800,000

Weighted-average period to recognize compensation expense

'3 years 1 month 6 days

Total number of unvested Stock option

10,000

11,363

Fair value Granted Amount

500,000

Stock-based compensation expense

2,866,000

1,112,000

6,752,000

1,865,000

100,000

300,000

Stock based compensation associated with restricted stock, recognition period

'1 year

Stock Based Compensation expense

$100,000

Stock options granted

1,176,733

355,454

Number of shares issued

34,642,539

31,202,542

Purchase price interest rate stock option

85.00%

Opportunity to purchase of common stock

327,272

ShareBased_Payments_Summary_of

Share-Based Payments - Summary of Activity of All Stock Incentive Plans (Detail) (USD $)	9 Months Ended	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'	'
Number of Stock Options, Outstanding, Beginning balance	3,846,168	'
Number of Stock Options, Granted	1,176,733	'
Number of Stock Options, Exercised	-1,128,065	'
Number of Stock Options, Forfeited/cancelled	-78,002	'
Number of Stock Options, Outstanding, Ending balance	3,816,834	3,846,168
Number of Stock Options, Exercisable	1,635,445	'
Number of Stock Options, Vested and expected to vest	3,373,444	'
Weighted-Average Exercise Price, Outstanding, Beginning balance	$4.14	'
Weighted-Average Exercise Price, Granted	$33.23	'
Weighted-Average Exercise Price, Exercised	$1.42	'
Weighted-Average Exercise Price, Forfeited/cancelled	$12.75	'
Weighted-Average Exercise Price, Outstanding, Ending balance	$13.74	$4.14
Weighted-Average Exercise Price, Exercisable	$2.02	'
Weighted-Average Exercise Price, Vested and expected to vest	$13.67	'
Weighted-Average Remaining Contractual Term (in years), Outstanding	'7 years 8 months 12 days	'7 years 5 months 5 days
Weighted-Average Remaining Contractual Term (in years), Exercisable	'6 years 4 days	'
Weighted-Average Remaining Contractual Term (in years), Vested and expected to vest	'7 years 6 months 26 days	'
Aggregate Intrinsic Value, Outstanding, Beginning balance	$76,189	'
Aggregate Intrinsic Value, Outstanding, Ending balance	181,726	76,189
Aggregate Intrinsic Value, Exercisable	97,023	'
Aggregate Intrinsic Value, Vested and expected to vest	$160,838	'

ShareBased_Payments_Summary_of1

Share-Based Payments - Summary of Unvested RSUs Activity (Detail) (Restricted Stock [Member])	9 Months Ended
	Sep. 30, 2014
Restricted Stock [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Unvested shares beginning of period	'
Granted	10,000
Vested	'
Unvested shares end of period	10,000

ShareBased_Payments_Unvested_R

Share-Based Payments - Unvested Restricted Stock Activity (Detail) (Restricted Stock [Member])	9 Months Ended
	Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Unvested shares beginning of period	'
Vested	'
Unvested shares end of period	10,000
Unvested [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Unvested shares beginning of period	23,295
Vested	-11,932
Unvested shares end of period	11,363

ShareBased_Payments_Recorded_S

Share-Based Payments - Recorded Stock-Based Compensation Expense for Employee and Non-Employee Stock Options and Restricted Stock (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'
Allocated share based compensation expense	$2,866	$1,112	$6,752	$1,865
Research and development expense [Member]	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'
Allocated share based compensation expense	1,438	919	3,899	1,452
General and administrative expense [Member]	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'
Allocated share based compensation expense	$1,428	$193	$2,853	$413

ShareBased_Payments_Schedule_o

Share-Based Payments - Schedule of Fair Value Option Award Weighted Average Assumptions Used (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'	'	'	'
Risk-free interest rate	1.95%	1.73%	1.83%	1.23%
Expected dividend yield	'	'	'	'
Expected term (in years)	'6 years	'6 years 1 month 2 days	'6 years 7 days	'6 years 4 months 10 days
Expected volatility	78.89%	94.25%	84.77%	92.60%

Income_Taxes_Benefit_Provision

Income Taxes - Benefit (Provision) for Income Taxes (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Current:	'	'	'	'
Federal	($448)	$121	($448)	$410
State	'	'	'	'
Total current	-448	121	-448	410
Deferred:	'	'	'	'
Federal	'	'	'	'
State	'	'	'	'
Total deferred	'	'	'	'
Total	($448)	$121	($448)	$410

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	1 Months Ended	9 Months Ended
Income Taxes - Additional Information (Detail) (USD $)	Jan. 31, 2014	Sep. 30, 2014	Aug. 31, 2014	Jun. 30, 2014	Dec. 31, 2013	Dec. 31, 2011
Income Taxes Disclosure [Line Items]	'	'	'	'	'	'
Amount of valuation allowance on deferred tax assets	'	'	'	'	'	$10,700,000
Income tax liability paid	5,958,000	5,958,000	'	'	'	'
Receive a refund from tax return	3,800,000	400,000	400,000	700,000	700,000	'
Interest and penalties paid	1,500,000	'	'	'	'	'
Unrecognized tax benefits	'	0	'	'	'	'
Federal [Member]	'	'	'	'	'	'
Income Taxes Disclosure [Line Items]	'	'	'	'	'	'
Receive a refund from tax return	'	$1,100,000	'	'	'	'

Recovered_Sheet1

Earnings Per Share Applicable to Common Stockholders - Calculation of Basic and Diluted Earnings Per Share (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]	'	'	'	'
Net income (loss) applicable to common stockholders	$3,704	($11,744)	($26,840)	($31,187)
Weighted-average shares:	'	'	'	'
Basic	34,495,076	22,744,486	33,176,801	10,111,735
Effect of dilutive securities:	'	'	'	'
Diluted	36,592,683	22,744,486	33,176,801	10,111,735
Net income (loss) per share:	'	'	'	'
Basic	$0.11	($0.52)	($0.81)	($3.08)
Diluted	$0.10	($0.52)	($0.81)	($3.08)
Stock Options and Restricted Stock Units [Member]	'	'	'	'
Effect of dilutive securities:	'	'	'	'
Stock options and restricted stock units	2,085,068	'	'	'
Restricted Stock [Member]	'	'	'	'
Effect of dilutive securities:	'	'	'	'
Unvested restricted stock	12,523	'	'	'
Stock options [Member]	'	'	'	'
Effect of dilutive securities:	'	'	'	'
Employee stock purchase plan options	16	'	'	'

Recovered_Sheet2

Earnings Per Share Applicable to Common Stockholders - Common Stock Excluded from Calculation of Diluted Net Loss Per Share (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'	'
Antidilutive securities excluded from computation of earnings per share	1,484,917	3,942,500	3,829,961	3,942,500
Stock Options and Restricted Stock Units [Member]	'	'	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'	'
Antidilutive securities excluded from computation of earnings per share	1,484,917	3,905,932	3,816,834	3,905,932
Restricted Stock [Member]	'	'	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'	'
Antidilutive securities excluded from computation of earnings per share	'	36,568	11,363	36,568
Employee Stock Purchase Plan Options [Member]	'	'	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'	'
Antidilutive securities excluded from computation of earnings per share	'	'	1,764	'

Commitments_and_Contingencies_1

Commitments and Contingencies - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
	sqft		Lease
			sqft
Schedule Of Commitments And Contingencies Future Maturities [Line Items]	'	'	'	'
Operating lease	74,498	'	74,498	'
Lease additional extended term	'	'	2	'
Number of years lease can be extended	'	'	'5 years	'
Stand by letter of credit	$1.40	'	$1.40	'
Initial lease term	'	'	'7 years	'
Lease agreement tenant incentive	11.2	'	11.2	'
Rent expense	$0.70	$0.50	$1.80	$1.60
Existing Leases [Member]	'	'	'	'
Schedule Of Commitments And Contingencies Future Maturities [Line Items]	'	'	'	'
Operating lease	38,536	'	38,536	'
Existing lease termination Period	'	'	'30 days	'

Commitments_and_Contingencies_2

Commitments and Contingencies - Future Annual Minimum Lease Payments Due Under Operating Lease (Detail) (USD $)	Sep. 30, 2014
In Thousands, unless otherwise specified	Sep. 30, 2014
Commitments and Contingencies Disclosure [Abstract]	'
2014	$677
2015	3,538
2016	4,318
2017	4,405
2018	4,493
Thereafter	15,826
Total minimum lease payments	$33,257