Agios Pharmaceuticals (AGIO) 10-K 16 Feb 17 2016 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2016	Feb. 14, 2017	Jun. 30, 2016
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
Trading Symbol	AGIO
Entity Registrant Name	AGIOS PHARMACEUTICALS INC
Entity Central Index Key	1,439,222
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		42,234,316
Entity Public Float			$ 1,189,342,604

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 160,754	$ 71,764
Marketable securities	380,560	245,238
Collaboration receivable - related party	4,886	8,225
Tenant improvement and other receivables	3,428	3,374
Prepaid expenses and other current assets	10,264	8,728
Total current assets	559,892	337,329
Marketable securities	32,250	58,905
Property and equipment, net	25,337	23,220
Other non-current assets	1,615	611
Total assets	619,094	420,065
Current liabilities:
Accounts payable	17,106	14,748
Accrued expenses	32,002	15,996
Deferred revenue - related party	35,913	19,665
Deferred rent	3,412	2,479
Total current liabilities	88,433	52,888
Deferred revenue, net of current portion - related party	154,297	4,699
Deferred rent, net of current portion	17,773	17,360
Commitments and contingencies (Note 6)
Stockholders' equity:
Preferred stock, $0.001 par value; 25,000,000 shares authorized, no shares issued and outstanding at December 31, 2016 and 2015
Common stock, $0.001 par value; 125,000,000 shares authorized and 42,220,444 and 37,696,502 shares issued and outstanding at December 31, 2016 and 2015, respectively	42	38
Additional paid-in capital	842,013	630,078
Accumulated other comprehensive loss	(313)	(318)
Accumulated deficit	(483,151)	(284,680)
Total stockholders' equity	358,591	345,118
Total liabilities and stockholders' equity	$ 619,094	$ 420,065

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
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	$ 0.001	$ 0.001
Common stock, shares authorized	125,000,000	125,000,000
Common stock, shares issued	42,220,444	37,696,502
Common stock, shares outstanding	42,220,444	37,696,502

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement [Abstract]
Collaboration revenue - related party	$ 69,892	$ 59,119	$ 65,358
Operating expenses:
Research and development (net of $19,714 and $25,173 of cost reimbursement from related party for the years ended December 31, 2016 and 2015, respectively)	220,163	141,827	100,371
General and administrative	50,714	35,992	19,120
Total operating expenses	270,877	177,819	119,491
Loss from operations	(200,985)	(118,700)	(54,133)
Interest income	2,514	968	203
Loss before income taxes	(198,471)	(117,732)	(53,930)
Benefit from income taxes			(426)
Net loss	$ (198,471)	$ (117,732)	$ (53,504)
Net loss per share - basic and diluted	$ (5.07)	$ (3.15)	$ (1.59)
Weighted-average number of common shares used in net loss per share - basic and diluted	39,126,400	37,429,262	33,667,024

Consolidated Statements of Ope5

Consolidated Statements of Operations (Parenthetical) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement [Abstract]
Cost reimbursement from related party	$ 19,714,000	$ 25,173,000	$ 0

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net loss	$ (198,471)	$ (117,732)	$ (53,504)
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale securities	5	(261)	(71)
Comprehensive loss	$ (198,466)	$ (117,993)	$ (53,575)

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Beginning balance, Value at Dec. 31, 2013	$ 131,482	$ 31	$ 244,881	$ 14	$ (113,444)
Beginning balance, Shares at Dec. 31, 2013		31,202,542
Unrealized gain (loss) on marketable securities	(71)			(71)
Net loss	(53,504)				(53,504)
Stock-based compensation expense	11,506		11,506
Vesting of restricted stock, Value	9		9
Vesting of restricted stock, Shares		14,773
Issuance of common stock upon exercise of stock options, Value	2,323	$ 1	2,322
Issuance of common stock upon exercise of stock options and employee stock purchase plan and vesting of restricted stock units		1,298,775
Issuance of stock, Value	332,621	$ 5	332,616
Issuance of stock, Shares		4,584,423
Ending balance, Value at Dec. 31, 2014	424,366	$ 37	591,334	(57)	(166,948)
Ending balance, Shares at Dec. 31, 2014		37,100,513
Unrealized gain (loss) on marketable securities	(261)			(261)
Net loss	(117,732)				(117,732)
Stock-based compensation expense	31,574		31,574
Vesting of restricted stock, Value	6		6
Vesting of restricted stock, Shares		8,522
Issuance of common stock upon exercise of stock options, Value	7,136	$ 1	7,135
Issuance of common stock upon exercise of stock options and employee stock purchase plan and vesting of restricted stock units		587,467
Issuance of stock, Value	29		29
Ending balance, Value at Dec. 31, 2015	345,118	$ 38	630,078	(318)	(284,680)
Ending balance, Shares at Dec. 31, 2015		37,696,502
Unrealized gain (loss) on marketable securities	5			5
Net loss	(198,471)				(198,471)
Stock-based compensation expense	42,086		42,086
Issuance of common stock upon exercise of stock options, Value	$ 7,703		7,703
Issuance of common stock upon exercise of stock options and employee stock purchase plan and vesting of restricted stock units	603,359	647,539
Issuance of stock, Value	$ 162,150	$ 4	162,146
Issuance of stock, Shares		3,876,403
Ending balance, Value at Dec. 31, 2016	$ 358,591	$ 42	$ 842,013	$ (313)	$ (483,151)
Ending balance, Shares at Dec. 31, 2016		42,220,444

Consolidated Statements of Sto8

Consolidated Statements of Stockholders' Equity (Parenthetical) $ in Millions	12 Months Ended
	Dec. 31, 2014USD ($)
Issuance costs of common stock	$ 0.9
Common Stock [Member]
Issuance costs of common stock	0.9
Additional Paid-In Capital [Member]
Issuance costs of common stock	$ 0.9

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities
Net loss	$ (198,471)	$ (117,732)	$ (53,504)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation	5,708	3,342	1,367
Net loss on disposal of fixed assets		33
Stock-based compensation expense	42,086	31,963	11,506
Net amortization of premiums and discounts on marketable securities	773	539	538
Changes in operating assets and liabilities:
Collaboration receivable - related party	3,339	(1,733)	(6,016)
Tenant improvement and other receivables	275	(1,040)	(2,334)
Prepaid expenses and other current and non-current assets	(2,695)	(3,768)	(2,878)
Accounts payable	3,501	4,215	7,577
Accrued expenses	16,854	1,633	5,231
Deferred rent	1,346	15,805	3,691
Refundable income taxes and income taxes payable		3,841	(5,303)
Deferred revenue - related party	165,846	(14,047)	(19,228)
Net cash provided by (used in) operating activities	38,562	(76,949)	(59,353)
Investing activities
Purchases of marketable securities	(506,067)	(353,177)	(837,219)
Proceeds from maturities and sales of marketable securities	396,632	501,650	505,528
Purchases of property and equipment	(9,915)	(20,164)	(2,216)
Release of restricted cash			571
Net cash (used in) provided by investing activities	(119,350)	128,309	(333,336)
Financing activities
Proceeds from public offering of common stock, net of commissions	162,150		333,577
Payment of public offering costs	(230)	(207)	(720)
Net proceeds from stock option exercises and employee stock purchase plan and vesting of restricted stock units	7,858	6,580	2,303
Net cash provided by financing activities	169,778	6,373	335,160
Net increase (decrease) in cash and cash equivalents	88,990	57,733	(57,529)
Cash and cash equivalents at beginning of the period	71,764	14,031	71,560
Cash and cash equivalents at end of the period	160,754	71,764	14,031
Supplemental cash flow information
Cash paid for income taxes			5,980
Supplemental disclosure of non-cash investing and financing transactions:
Vesting of restricted stock		6	9
Additions to property, plant and equipment included in accounts payable and accrued expenses	73	2,163	2,118
Proceeds from stock option exercises in other current assets	32	$ 186	20
Public offering costs in other current assets, net of amounts in accounts payable and accrued expenses	$ 230		$ 236

Nature of Business

Nature of Business	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business	1. Nature of Business 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 and rare genetic metabolic disorders. 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. Agios’ therapeutic areas of focus are cancer and rare genetic metabolic disorders, 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 as a platform to create transformative therapies. The Company is located in Cambridge, Massachusetts. Liquidity The Company has an accumulated deficit as of December 31, 2016 of $483.2 million and will require substantial capital for research and product development. The future success of the Company is dependent on its ability to develop its product candidates and ultimately upon its ability to attain profitable operations. The Company is subject to a number of risks similar to other life science companies, including, but not limited to, risks related to the successful discovery and development of its drug candidates, raising additional capital, development of new technological innovations by its competitors, protection of proprietary technology, and market acceptance of the Company’s products. In September 2016, the Company completed a public offering of 3,370,786 shares of its common stock at a public offering price of $44.50 per share. The Company received net proceeds from this offering of $141.0 million, after deducting underwriting discounts and commissions paid by the Company. In addition, the Company granted the underwriters the option to purchase up to an additional 505,617 shares of its common stock which option was exercised in September 2016 resulting in additional net proceeds to the Company of $21.1 million, after deducting underwriting discounts and commissions paid by the Company. In addition to the Company’s existing cash, cash equivalents and marketable securities, the Company is eligible to earn a significant amount of milestone payments and is entitled to additional cost reimbursements under its collaboration agreements with Celgene Corporation and related subsidiaries (“Celgene”). At December 31, 2016, the Company believes its cash, cash equivalents and marketable securities, totaling $573.6 million, are sufficient to fund operations for a period of at least one year from the issuance date of the financial statements.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Principles of consolidation The Company’s consolidated financial statements include the Company’s accounts and the accounts of the Company’s wholly owned subsidiaries, Agios Securities Corporation and Agios International Sarl. All intercompany transactions have been eliminated in consolidation. The consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles (“GAAP”). Use of estimates The preparation of financial statements in conformity with U.S. GAAP requires the Company’s management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances. Actual results could differ from those estimates. Revenue recognition The Company recognizes revenue in accordance with the Financial Accounting Standards Board’s (“FASB”) Accounting Standards Codification (“ASC”) 605, Revenue Recognition • persuasive evidence of an arrangement exists; • delivery has occurred or services have been rendered; • the seller’s price to the buyer is fixed or determinable; and • collectability is reasonably assured. Collaboration Agreements with Celgene To date, the Company’s revenue has primarily been generated from its collaboration agreements with Celgene, a related party through ownership of the Company’s common stock, (collectively, “Collaboration Agreements”). In April 2010, the Company entered into a collaboration agreement focused on cancer metabolism. The agreement was amended in October 2011 and July 2014 (the agreement together with the amendments, the “2010 Agreement”). On April 27, 2015, the Company entered into a joint worldwide development and profit share collaboration and license agreements (collectively, the “AG-881 AG-881 AG-881 Collaboration and license revenue In January 2011, the Company adopted FASB Accounting Standards Update (“ASU”) No. 2009-13, Multiple-Element Revenue Arrangements (“ASU 2009-13”) , 605-25, In July 2014, the Company amended its 2010 Agreement. The amendment was determined to be a material modification pursuant to ASU 2009-13. 605-25, AG-881 605-25. Pursuant to ASC 605-25, • delivered item or items have value to the customer on a standalone basis, and • if the arrangement includes a general right of return relative to the delivered item or items, delivery or performance of the undelivered item or items is considered probable and substantially in the control of the vendor. If a deliverable meets both criteria above, it is considered a separate unit of accounting. If a deliverable does not meet both criteria above, it will be evaluated in combination with other deliverables and, if appropriate, aggregated to form one unit of accounting. The arrangement consideration is then allocated to each unit of accounting based on the relative selling price, using the Company’s best estimate of selling price of each unit of accounting, if vendor specific objective evidence or third party evidence is not available. The provisions of ASC 605-25 The Company recognizes revenue for the units of accounting over the term of the related contract or as undelivered items are delivered (proportional performance method), as appropriate. Under the proportional performance method, the consideration allocated to each unit of accounting is recognized as revenue based on the ratio of the level of effort incurred to date compared to the total estimated level of effort required to complete the Company’s performance obligations under the unit of accounting. Determining the total estimated level of effort required to complete all performance obligations requires management judgment and estimation, including assumptions regarding future operating performance, the timelines of the clinical trial approvals and the estimated patient populations. Reimbursement of research and development costs under the Company’s Collaboration Agreements are recognized as revenue, provided the Company has determined that it is acting primarily as a principal in the transaction according to the provisions outlined in FASB ASC 605-45, Revenue Recognition – Principal Agent Considerations 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. Milestone revenue The Company applies the provisions of ASC 605-28, Revenue Recognition – Milestone Method 605-28, Revenue from milestones, if they are nonrefundable and deemed substantive, are recognized upon achievement of the milestones. The Company recognizes revenue associated with non-substantive Research and development costs Research and development costs are expensed as incurred. Research and development costs include salaries and personnel-related costs, consulting fees, fees paid for contract research services, fees paid to clinical research organizations and other third parties associated with clinical trials, the costs of laboratory equipment and facilities, and other external costs. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are delivered or the services are performed. Stock-based compensation The Company accounts for its stock-based compensation awards in accordance with ASC 718, Compensation –Stock Compensation . Stock-based payments issued to non-employees Equity non-employees, Income taxes Income taxes are recorded in accordance with ASC 740, Accounting for Income Taxes The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. The Company evaluated whether any uncertain tax positions arise from commencing operations of its wholly owned subsidiary, Agios International Sarl, and determined no uncertain tax positions existed. As of December 31, 2016 and 2015, the Company does not have any uncertain tax positions. Comprehensive income (loss) Comprehensive income (loss) is defined as the change in equity of a business enterprise during a period from transactions, and other events and circumstances from non-owner available-for-sale available-for-sale Cash and cash equivalents The Company considers highly liquid investments with a maturity of three months or less when purchased to be cash equivalents. Cash equivalents, which consist primarily of money market funds and corporate debt securities, are stated at fair value. Marketable securities Marketable securities at December 31, 2016 and 2015 consisted primarily of investments in certificates of deposits, United States Treasuries, government securities and corporate debt securities. 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 Investments – Debt and Equity Securities 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 consolidated 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 December 31, 2016 consisted of the following (in thousands): Amortized Cost Unrealized Unrealized Fair Current: Certificates of deposit $ 11,280 $ 2 $ (3 ) $ 11,279 U.S. Treasuries 141,678 2 (62 ) 141,618 Government securities 19,533 — (23 ) 19,510 Corporate debt securities 208,285 3 (135 ) 208,153 Non-current: Certificates of deposit 7,600 6 (13 ) 7,593 Government securities 4,499 — (21 ) 4,478 Corporate debt securities 20,248 — (69 ) 20,179 $ 413,123 $ 13 $ (326 ) $ 412,810 Marketable securities at December 31, 2015 consisted of the following (in thousands): Amortized Unrealized Unrealized Fair Current: Certificates of deposit $ 11,248 $ — $ (5 ) $ 11,243 U.S. Treasuries 234,130 10 (145 ) 233,995 Non-current: U.S. Treasuries 59,083 — (178 ) 58,905 $ 304,461 $ 10 $ (328 ) $ 304,143 At December 31, 2016 and 2015, the Company held both current and non-current non-current available-for-sale. At December 31, 2016 and 2015, the Company held 158 and 74 debt securities, respectively, that were in an unrealized loss position. The aggregate fair value of debt securities in an unrealized loss position at December 31, 2016 and 2015 was $335.4 million and $207.4 million, respectively. There were no individual securities that were in a significant unrealized loss position or that had been in an unrealized loss position for greater than one year as of December 31, 2016 and 2015. 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 December 31, 2016 and 2015. Concentrations of credit risk Financial instruments which potentially subject the Company to credit risk consist primarily of cash, cash equivalents and marketable securities. The Company holds these investments in highly rated financial institutions, and, by policy, limits the amounts of credit exposure to any one financial institution. These amounts at times may exceed federally insured limits. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to any significant credit risk on these funds. The Company has no off-balance The Company is also subject to credit risk from its collaboration receivable. The Company evaluates the creditworthiness of its collaborator and has determined it is credit worthy. To date the Company has not experienced any losses with respect to its collaboration receivable. Fair value measurements The Company records cash equivalents and marketable securities at fair value. ASC 820, Fair Value Measurements and Disclosures Level 1 – Level 2 – Level 3 – The following table summarizes the cash equivalents and marketable securities measured at fair value on a recurring basis as of December 31, 2016 (in thousands): Level 1 Level 2 Level 3 Total Cash equivalents $ 143,352 $ 7,897 $ — $ 151,249 Marketable securities: Certificates of deposit — 18,872 — 18,872 U.S. Treasuries 141,618 — — 141,618 Government securities 11,514 12,474 — 23,988 Corporate debt securities — 228,332 — 228,332 $ 296,484 $ 267,575 $ — $ 564,059 The following table summarizes the cash equivalents and marketable securities measured at fair value on a recurring basis as of December 31, 2015 (in thousands): Level 1 Level 2 Level 3 Total Cash equivalents $ 59,332 $ — $ — $ 59,332 Marketable securities: Certificates of deposit — 11,243 — 11,243 U.S. Treasuries 292,900 — — 292,900 $ 352,232 $ 11,243 $ — $ 363,475 Cash equivalents and marketable securities have been initially valued at the transaction price and subsequently revalued, 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. After completing its validation procedures, the Company did not adjust or override any fair value measurements provided by the pricing services as of December 31, 2016 or 2015. There have been no changes to the valuation methods during the years ended December 31, 2016 and 2015. The Company evaluates transfers between levels at the end of each reporting period. Due to the lack of an active market, the Company transferred $11.0 million of government securities from Level 1 to Level 2 during the year ended December 31, 2016. There were no transfers of assets or liabilities between Level 1 and Level 2 during the year ended December 31, 2015. The Company had no financial assets or liabilities that were classified as Level 3 at any point during the years ended December 31, 2016 and 2015. Due to their short-term nature, the carrying amounts reflected in the consolidated balance sheets for cash, collaboration receivable – related party, tenant improvement and other receivables, prepaid expenses and other current and non-current Collaboration and other receivables Collaboration receivables as of December 31, 2016 and 2015 represent amounts due under our Collaboration Agreements for reimbursements of certain costs. Other receivables represent amounts due from the Company’s landlord for reimbursement of tenant improvements under the Company’s lease agreement. The Company estimates an allowance for doubtful accounts based on credit worthiness, historical payment patterns, aging of accounts receivable balances, and general economic conditions. As of December 31, 2016 and 2015, the Company had no allowance for doubtful accounts. Property and equipment Property and equipment consist of laboratory equipment, computer equipment and software, leasehold improvements, furniture and fixtures, and office equipment. Property and equipment is stated at cost, and depreciated using the straight-line method over the estimated useful lives of the respective assets: Laboratory equipment 5 years Computer equipment and software 3 years Leasehold improvements Shorter of asset’s useful life or remaining term of lease Furniture and fixtures 5 years Office equipment 5 years Costs of major additions and betterments are capitalized; maintenance and repairs, which do not improve or extend the life of the respective assets, are charged to expense as incurred. Upon retirement or sale, the cost of the disposed asset and the related accumulated depreciation are removed from the accounts and the resulting gain or loss is recognized. Impairment of long-lived assets The Company periodically evaluates its long-lived assets for potential impairment in accordance with ASC 360, Property, Plant and Equipment Segment and geographic information Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker, or decision-making group, in making decisions on how to allocate resources and assess performance. The Company’s chief operating decision maker is the chief executive officer. The Company and the chief operating decision maker view the Company’s operations and manage its business as one operating segment. Net loss per share Basic net loss per share is calculated by dividing net loss by the weighted-average shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share 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 the dilutive net loss per share calculation, stock options, including performance-based stock options which were determined to be probable of achievement, restricted stock units, unvested restricted stock and employee stock purchase plan shares are considered to be common stock equivalents but are excluded from the calculation of diluted net loss per share as their effect would be anti-dilutive. Since the Company had a net loss for all periods presented, the effect of all potentially dilutive securities is anti-dilutive. Accordingly, basic and diluted net loss per share was the same for the years ended December 31, 2016, 2015 and 2014. Furthermore, 323,339 performance-based stock options and stock units that were previously granted had not vested as of December 31, 2016 and were excluded from diluted shares outstanding as the vesting conditions for the awards, discussed further in Note 8 “Share-Based Payments,” had not been met as of December 31, 2016. The following common stock equivalents were excluded from the calculation of diluted net loss per share applicable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: Years ended December 31, 2016 2015 2014 Stock options 5,218,880 4,618,697 3,795,420 Restricted stock units 77,050 15,000 10,000 Unvested restricted stock — — 8,522 Employee stock purchase plan shares 24,018 7,721 7,159 5,319,948 4,641,418 3,821,101 Recent accounting pronouncements Revenue from Contracts with Customers In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) 2014-09”). 2015-14, Revenue from Contracts with Customers (Topic 606) 2014-09; No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net) 2014-09; No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing 2014-09; No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients 2014-09 The Revenue ASUs provide an accounting standard 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, 2017, with an option to early adopt for interim and annual periods beginning after December 15, 2016. The guidance permits two methods of adoption: retrospectively to each prior reporting period presented (the full retrospective method), or retrospectively with the cumulative effect of initially applying the guidance recognized at the date of initial application (the modified retrospective method). We currently anticipate adoption of the new standard effective January 1, 2018 under the modified retrospective method. The Company is in the process of determining the impact of the Revenue ASUs on its financial statements; however, the adoption of the Revenue ASUs is expected to have a significant impact on the Company’s notes to consolidated financial statements and its internal controls over financial reporting. Other Recent Accounting Pronouncements In October, 2016, the FASB issued ASU No. 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory 2016-16”), 2016-16 In March 2016, the FASB issued ASU No. 2016-09, Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting 2016-09”), 2016-09 In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) 2016-02”), 2016-02 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. Subsequent events The Company considered events or transactions occurring after the balance sheet date, but prior to the issuance of the consolidated financial statements, for potential recognition or disclosure in its consolidated financial statements. All significant subsequent events have been properly disclosed in the consolidated financial statements.

Celgene Collaboration Agreement

Celgene Collaboration Agreements	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Celgene Collaboration Agreements	3. Celgene Collaboration Agreements 2016 Agreement On May 17, 2016, Agios entered into the 2016 Agreement, which establishes a global collaboration focused on the research and development of immunotherapies against certain metabolic targets that exert their antitumor efficacy primarily via the immune system. In addition to new programs identified under the 2016 Agreement, both parties have also agreed that all future development and commercialization of two remaining cancer metabolism programs discovered under the 2010 Agreement, including a program focused on methylthioadenosine phosphorylase, or MTAP, deleted cancers, will now be governed by the 2016 Agreement. During the research term of the 2016 Agreement, the Company plans to conduct research programs focused on discovering compounds that are active against metabolic targets in the immuno-oncology (“IO”) field. The initial four-year research term will expire on May 17, 2020. The research term may be extended for up to two, or in specified cases, up to four additional one-year For each program under the 2016 Agreement, Agios may nominate compounds that meet specified criteria as development candidates and, in limited circumstances, Celgene may also nominate compounds as development candidates for each such program. Celgene may designate the applicable program for further development following any such nomination, after which the Company may conduct, at the Company’s expense, additional pre-clinical At the end of the research term, Celgene may designate for continued development up to three research programs for which development candidates have yet to be nominated, which are referred to as continuation programs. Agios may conduct further research and pre-clinical The Company has granted Celgene the right to obtain exclusive options to development and commercialization rights for each program that Celgene has designated for further development and for each continuation program. Celgene may exercise each such option beginning on the designation of a development candidate for such program (or on the designation of such program as a continuation program) and ending on the earlier of the end of a specified period after Celgene is furnished with specified information about the initial phase 1 dose escalation study for such program, or January 1, 2030. Research programs that have applications in the inflammation or autoimmune (“I&I”) field that may result from the 2016 Agreement will also be subject to the exclusive options described above. Agios will retain rights to any program that Celgene does not designate for further development or does not exercise its option. Under the terms of the 2016 Agreement, following Celgene’s exercise of its option with respect to a program, the parties will enter into either a co-development co-commercialization co-development co-commercialization co-develop co-commercialize Co-development co-commercialization Under each co-development co-commercialization program-by-program License agreements Under each license agreement under the 2016 Agreement, Celgene will be responsible for all post-option-exercise worldwide development and associated costs, subject to specified exceptions, as well as worldwide commercialization and associated costs, for licensed products. Financial terms Under the terms of the 2016 Agreement, the Company received an initial upfront payment in the amount of $200.0 million. The 2016 Agreement provides specified rights to extend the research term for up to two, or in specified cases, up to four, additional years by paying a $40.0 million per-year For the co-development co-commercialization co-development co-commercialization For each licensed program in the I&I field, Agios is eligible to receive royalties at tiered, low double-digit percentage rates on Celgene’s net sales, if any, of the applicable licensed products and up to $386.3 million in potential milestone-based payments. The potential milestone-based payments for such programs are comprised of: (i) a $25.0 million milestone-based payment upon achievement of a specified clinical development event, (ii) up to $236.3 million in milestone-based payments upon achievement of specified regulatory milestone events, and (iii) up to $125.0 million in milestone-based payments upon achievement of specified commercial milestone events. Opt-out Under the 2016 Agreement, the Company may elect to opt out of the cost and profit share under any co-development co-commercialization Term The term of the 2016 Agreement commenced on May 17, 2016 and, if not terminated earlier, will expire upon later of the last-to-expire last-to-exist co-development co-commercialization Termination Subject to specified exceptions, Celgene may terminate the 2016 Agreement in its entirety for any reason by providing Agios with prior written notice if there are no active co-development co-commercialization program-by-program co-development co-commercialization program-by-program co-development co-commercialization co-development co-commercialization co-development co-commercialization Exclusivity While any of Celgene’s options remain available under the 2016 Agreement, subject to specified exceptions, the Company may not directly or indirectly develop, manufacture or commercialize, outside of the 2016 Agreement, any therapeutic modality in the IO field or the I&I field with specified activity against a metabolic target. During the term of each co-development co-commercialization AG-120 On May 17, 2016, Agios entered into a letter agreement regarding ivosidenib (AG-120) “AG-120 AG-120 (AG-120) AG-120 (AG-120) (AG-120) AG-120 AG-120 AG-120 AG-881 AG-881 On April 27, 2015, the Company entered into the AG-881 AG-881 AG-881 AG-881 AG-881 The Company is eligible to receive up to $70.0 million in potential milestone payments related to AG-881 AG-881 low- mid-teen AG-881. 2010 Agreement and amendments In April 2010, the Company entered into the 2010 Agreement. The 2010 Agreement was amended in October 2011 and July 2014. The goal of the collaboration was to discover, develop and commercialize disease-altering therapies in oncology based on the Company’s cancer metabolism research platform. The Company initially led discovery, preclinical and early clinical development for all cancer metabolism programs under the collaboration. The discovery phase of the 2010 Agreement expired in April 2016. Upon agreement to terminate the 2010 Agreement, effective as of August 15, 2016, as to the program directed to the IDH1 target, for which ivosidenib (AG-120) co-commercialized Under the 2010 Agreement, the Company is eligible to receive up to $120.0 million in potential milestone payments for the enasidenib program. The potential milestone payments are comprised of: (i) a $25.0 million milestone payment upon achievement of a specified clinical development milestone event, which was earned upon the initiation of the IDHENTIFY clinical trial, (ii) up to $70.0 million in milestone payments upon achievement of specified ex-U.S. Under the 2010 Agreement, the Company may also receive royalties at tiered, low- mid-teen Unless terminated earlier by either party, the term of the 2010 Agreement will continue until the expiration of all royalty terms with respect to enasidenib. Celgene may terminate this agreement for convenience in its entirety upon ninety days written notice to the Company. If either party is in material breach and fails to cure such breach within the specified cure period, the other party may terminate the 2010 Agreement in its entirety. Either party may terminate the agreement in the event of specified insolvency events involving the other party. Accounting analysis and revenue recognition–collaboration revenue Pre-July Prior to the July 2014 amendment of the 2010 Agreement, 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 2010 Agreement. Upfront consideration of approximately $121.2 million 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. 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 recognized the premium as revenue on a straight-line basis over the performance period. For the period January 1, 2014 through the July 2014 amendment date, the Company recognized a total of $42.7 million in revenue under the previous accounting guidance and upon the modification. July 2014 – April 2015 The July 2014 amendment of the 2010 Agreement was determined to be a material modification of the 2010 Agreement due to the change in the total potential consideration that was more than insignificant and significant changes to certain of the deliverables in the arrangement. Upon concluding that the 2010 Agreement had been materially modified in July 2014, the Company identified the remaining deliverables under the arrangement and determined its best estimates of selling price for the undelivered elements as of the modification date as vendor specific objective evidence and third-party evidence were not available. 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 arrangement consideration and the best estimate of selling price of the undelivered items was recognized as revenue at the modification date. The undelivered items from the July 2014 modification, the related best estimate of selling price, the method of recognizing the allocated consideration, and the revenue recognized related to each unit of accounting through April 27, 2015, the effective date of the AG-881 • License for the split licensed program–ivosidenib (AG-120): non-contingent • Development services for five separate on-going on-going on-going on-going non-contingent • On-going non-contingent • 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 was recognized as revenue ratably over the performance period. During the period January 1, 2015 through April 27, 2015 and for the period July 2014 through December 31, 2014, the Company recognized the non-contingent In December 2014, Celgene elected to extend the term of the discovery period over which the Company was providing on-going Beginning in the first quarter of 2015, the parties agreed to plans to advance enasidenib into later stage development studies. Pursuant to the terms of the 2010 Agreement, the parties agreed to transition primary development responsibilities for enasidenib to Celgene for later stage development at which point Celgene became the lead development party for enasidenib. During the transition, the Company continued to manage certain arrangements with third-party service providers whose contracts were assigned to Celgene. The Company determined it is no longer the primary obligor of these arrangements and, when considering the other factors included within ASC 605-45, re-assessed on-going During the period January 1, 2015 through April 27, 2015, the execution date of the AG-881 April 2015 – May 2016 The AG-881 AG-881 AG-881 AG-881 AG-881 • Licenses for the AG-881 non-contingent AG-881 non-contingent non-contingent • Four separate on-going on-going 605-45, non-contingent non-contingent • Four separate on-going on-going 605-45, non-contingent non-contingent • On-going non-contingent non-contingent • Committee participations under the 2010 Agreement and AG-881 non-contingent non-contingent The total estimated arrangement consideration, as well as the expected timing of revenue recognition, is adjusted based on changes in estimated arrangement consideration as a result of changes in estimates for on-going catch-up in-process As a result of Celgene assuming the primary development responsibilities for enasidenib in the first quarter of 2015, the Company recorded $0.9 million of third-party costs incurred on behalf of Celgene, during period January 1, 2016 through May 17, 2016, and $3.0 million, for the period April 27, 2015 through December 31, 2015, as a reduction of research and development costs. Beginning in the third quarter of 2015, the Company initiated a phase 1b frontline combination clinical trial of enasidenib and ivosidenib (AG-120) 605-45, (AG-120) (AG-120) During the period January 1, 2016 through May 17, 2016, the Company incurred an additional $4.4 million in reimbursable development expenses related to the ivosidenib (AG-120) AG-881 Post-May The 2016 Agreement, executed on May 17, 2016, was determined to be a modification of the 2010 Agreement and the AG-881 • Three separate development services for which the Company determined it is acting as the principal of all development activities (each of which is a separate unit of accounting): The Company developed the best estimate of selling price for all three of the development services of $67.8 million using management’s best estimate of the cost of obtaining these services at arm’s length from a third-party provider, as well as internal full time equivalent costs to support the development services. The estimated costs were determined to represent management’s best estimate of the price these services could be sold for separately. The amount allocated to these units of accounting is being recognized as revenue on a proportional performance basis as services are provided. The Company expects the services to be performed through 2019. When considering the factors included within ASC 605-45, non-contingent • Three separate on-going 605-45, non-contingent • On-going non-contingent • Committee participations under the Collaboration Agreements: The Company developed the best estimate of selling price of the committee participation services of $1.5 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 is being recognized as revenue ratably over the expected performance period, December 2022. For the period May 17, 2016 through December 31, 2016, the Company recognized the non-contingent • Additional development activities for which the Company determined it is acting as the principal of all development activities: The Company developed the best estimate of selling price of the development service of $48.7 million using management’s best estimate of the cost of obtaining these services at arm’s length from a third-party provider, as well as internal full time equivalent costs to support the development services. The estimated costs were determined to represent management’s best estimate of the price these services could be sold for separately. The activities under this unit of accounting are not expected to begin until 2020. When considering the factors included within ASC 605-45, The total estimated arrangement consideration, as well as the expected timing of revenue recognition, is adjusted based on changes in estimated arrangement consideration as a result of changes in estimates for on-going catch-up in-process During the three months ended December 31, 2016, the Company reached a preclinical achievement for a program that resulted in a change in estimate of total level of effort required for that program. This change in estimate resulted in the recognition of an additional $10.8 million of revenue and reduced our net loss by the same amount for the year ended December 31, 2016. This also resulted in a decrease in net loss per share of $0.28 over the same period. As a result of Celgene assuming the primary development responsibilities for enasidenib in the first quarter of 2015, the Company recorded $1.0 million of third-party costs incurred on behalf of Celgene for the period May 17, 2016 through December 31, 2016 as a reduction of research and development costs. During the period May 17, 2016 through December 31, 2016, the Company incurred an additional $0.2 million in reimbursable development expenses related to the enasidenib program that were not contemplated as of the May 2016 modification. The amount is recorded as collaboration revenue. During the years ended December 31, 2016, 2015 and 2014, the Company recognized a total of $44.9 million $59.1 million and $65.4 million, respectively, as collaboration revenue. The Company recognized $19.7 million, $25.2 million as a reduction of research and development expenses during the years ended December 31, 2016 and 2015, respectively. The Company did not recognize any reduction to research and development expenses in the year ended December 31, 2014. 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. As of December 31, 2016 and 2015, the Company has recorded a collaboration receivable of $4.9 million and $8.2 million, respectively, related to reimbursable development costs. Accounting analysis and revenue recognition – milestone revenue The Company concluded that certain of the clinical development and regulatory milestone payments that may be received under the Collaboration Agreements, 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. Revenue from substantive milestones, if they are nonrefundable, is recognized as revenue upon successful accomplishment of the milestones. Clinical and regulatory milestones are deemed non-substantive Non-substantive In January 2016, a substantive clinical development milestone related to the enasidenib program under the 2010 Agreement was achieved and the Company received a milestone payment of $25.0 million, which was recognized as collaboration revenue during the three months ended March 31, 2016. No other milestones were earned during the years ended December 31, 2016, 2015 and 2014. The next potential milestones expected to be achieved under the Collaboration Agreements relate to specified ex-U.S. regulatory events. Achievement of these events will result in milestone payments of up to $70.0 million.

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Property and Equipment	4. Property and Equipment Property and equipment consists of the following (in thousands): December 31, 2016 2015 Laboratory equipment $ 14,529 $ 9,751 Computer equipment and software 3,204 2,029 Leasehold improvements 19,858 15,853 Furniture and fixtures 748 413 Office equipment 233 206 Construction in progress 137 2,632 Total property and equipment 38,709 30,884 Less accumulated depreciation (13,372 ) (7,664 ) Total property and equipment, net $ 25,337 $ 23,220 Depreciation expense for the years ended December 31, 2016, 2015 and 2014 was $5.7 million, $3.3 million and $1.4 million, respectively.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	12 Months Ended
	Dec. 31, 2016
Payables and Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	5. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consist of the following (in thousands): December 31, 2016 2015 Accrued compensation $ 11,092 $ 7,005 Accrued contracted research and development costs 20,266 7,449 Accrued professional fees 476 228 Accrued other 168 1,314 Total $ 32,002 $ 15,996

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	6. Commitments and Contingencies Operating lease On September 15, 2014, the Company entered into an operating lease agreement (the “Lease”) for approximately 74,500 square feet of office and laboratory space located at 88 Sidney Street, Cambridge, Massachusetts. Concurrently, the Company also entered into an agreement to terminate its preexisting lease under which the Company leased approximately 38,500 square feet of office and laboratory space located at 38 Sidney Street, Cambridge, Massachusetts. On November 21, 2014, the Company entered into a first amendment to the Lease (the “First Amendment”) to expand the rentable square footage of the leased space at 88 Sidney Street to approximately 113,200 square feet. The Company became responsible for paying rent under the Lease as amended by the First Amendment on May 15, 2015. The Company’s lease at 38 Sidney Street terminated on June 15, 2015. On July 20, 2015, the Company entered into a second amendment to the Lease (the “Second Amendment”) to expand the rentable square footage at 88 Sidney Street to approximately 146,030 square feet. The Company became responsible for paying for the additional space under the Second Amendment on November 1, 2015. The initial term of the Lease, including both amendments, will terminate on May 15, 2022. At the end of the initial lease term, the Company has the option to extend the Lease for two consecutive terms of five years at the fair market rent at the time of the extension. The Company gained physical access to the original space per the Lease in September 2014, the expanded space under the First Amendment in November 2014 and the expanded space under the Second Amendment in July 2015. Rent expense is recorded on a straight-line basis from the date physical access to the space was provided through the end of the lease term. The Lease, including both amendments, contains rent escalation clauses and a tenant improvement allowance of $20.5 million. The Company provided a standby letter of credit of $2.9 million as security for its obligations under the Lease and both amendments in July 2015. The Company was not required to maintain any cash collateral for the standby letter of credit. As of December 31, 2016 and 2015, the Company recorded approximately $3.1 million and $3.4 million, respectively, in tenant improvement allowance to be received from the Company’s landlord. Amounts received for tenant improvements, which are considered normal tenant improvements are recorded as leasehold improvements within property and equipment, net, or construction in progress and in deferred rent and deferred rent, net of current portion, in the consolidated balance sheets. The deferred rent will be recorded as a reduction in rent expense ratably over the lease term. Future annual minimum lease payments due under non-cancellable 2017 $ 9,050 2018 9,278 2019 9,511 2020 9,751 2021 9,996 Thereafter 3,903 $ 51,489 Rent expense was $6.0 million, $7.1 million and $3.7 million for the years ended December 31, 2016, 2015 and 2014, respectively. The operating lease requires 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. Program license agreements The Company has entered into various cancelable license agreements for certain technology. None of the Company’s lead product candidates utilize technology covered by these licenses. During the years ended December 31, 2016 and 2015, the Company paid annual maintenance payments totaling $70,000 and $53,000, respectively, to certain of the licensors, which are recorded as research and development expense. The Company has the option to renew these licenses on an annual basis in exchange for payments approximating $70,000 for 2017. The Company could be required to make patent-related, clinical development, regulatory and sales-based milestone payments of up to $0.1 million, $1.6 million, $5.4 million and $3.7 million, respectively, to the licensors. As of December 31, 2016, the Company accrued $75,000 and $500,000 related to patent milestones and clinical milestones, respectively, that have been achieved. The license agreements also require the Company to remit royalties in amounts ranging from 0.5% to 2.5% based on net sales of products utilizing the licensed technology. The Company is also required to make payments in amounts ranging from 7.0% to 25.0% for non-royalty Milestone payment agreements The Company entered into an agreement with a service provider to receive discounted upfront labor costs for a defined program in consideration of a milestone payment in five years from the Effective Date, as defined in the agreement. The milestone is dependent on the Company declaring a development candidate within the five-year contract term and is dependent on the origins of the development candidate. If the development candidate is derived from a new chemical class created by the service provider, the milestone will be two times the discounted upfront labor costs. If the development candidate is not derived from a new chemical class created by the service provider, the milestone will be equal to the discount on services provided to date. No milestone payment is due if no development candidate is declared within the five year period. In addition, should no development candidate be declared within three years and the Company remains active with the program, the service provider may, at its discretion, elect to request reimbursement of the discount on services provided to date and forgo the milestone payment. The election must be provided in writing within thirty days of the end of the three-year period. The Company has accrued a milestone payment of $4.1 million for the accumulated discounted labor costs as of December 31, 2016. Legal contingencies From time to time, the Company may be involved in disputes and legal proceedings in the ordinary course of its business. These proceedings may include allegations of infringement of intellectual property, employment or other matters. The Company does not have any ongoing legal proceedings that, based on management estimates, could have a material effect on the Company’s consolidated financial statements.

Common Stock

Common Stock	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Common Stock	7. Common Stock The Company’s common stock has the following characteristics: Voting The holders of shares of common stock are entitled to one vote for each share of common stock held at all meetings of stockholders and written actions in lieu of meetings. Dividends The holders of shares of common stock are entitled to receive dividends, if and when declared by the board of directors and are subject to any preferential dividend or other right of any then outstanding preferred stock. No dividends have been declared or paid since the Company’s inception. Liquidation The holders of shares of common stock are entitled to share ratably in the Company’s assets available for distribution to stockholders, in the event of any voluntary or involuntary liquidation, subject to any preferential or other rights of any then outstanding preferred stock.

Share-Based Payments

Share-Based Payments	12 Months Ended
	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Payments	8. Share-Based Payments Stock incentive plans 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 Company’s initial public offering and provides for the grant of incentive stock options, non-qualified During the years ended December 31, 2016, 2015 and 2014 the Company did not grant any stock options to consultants and advisors of the Company. The following table summarizes the stock option activity of all stock incentive plans for the year ended December 31, 2016. Number of Weighted- Weighted- Aggregate Outstanding at December 31, 2015 4,618,697 $ 44.45 7.49 $ 153,573 Granted 1,556,240 43.99 Exercised (603,359 ) 10.84 Forfeited/Expired (352,698 ) 65.21 Outstanding at December 31, 2016 5,218,880 $ 46.79 7.28 $ 63,559 Exercisable at December 31, 2016 2,527,605 $ 36.50 5.85 $ 53,952 Vested and expected to vest at December 31, 2016 5,065,064 $ 46.43 7.23 $ 63,351 The weighted-average grant date fair value of options granted was $28.41, $65.38 and $27.26 during the years ended December 31, 2016, 2015 and 2014, respectively. The total intrinsic value of options exercised was $26.4 million $50.9 million and $60.4 million during the years ended December 31, 2016, 2015 and 2014, respectively. At December 31, 2016, the total unrecognized compensation expense related to unvested stock option awards, including estimated forfeitures, was $81.7 million, which the Company expects to recognize over a weighted-average period of approximately 2.5 years. The Company also has unrecognized stock-based compensation expense of $11.6 million related to stock units with performance-based vesting criteria that are not considered probable of achievement as of December 31, 2016. Restricted stock units The Company may grant awards of restricted stock units (“RSUs”) to non-employee The Company granted 69,550 RSUs, 15,000 RSUs and 10,000 RSUs during the years ended December 31, 2016, 2015 and 2014, respectively. The Company recorded stock-based compensation expense related to RSUs of $2.0 million, $0.9 million and $0.1 million for the years ended December 31, 2016, 2015 and 2014, respectively. These amounts are included in the total stock-based compensation expense disclosed within the table contained in the “Stock-based compensation expense” section of this footnote. As of December 31, 2016, there was approximately $2.1 million of total unrecognized compensation expense related to RSUs, which is expected to be recognized over a weighted-average period of 1.1 years. The following table presents RSU activity for the year ended December 31, 2016: Number of Weighted-average Unvested shares at December 31, 2015 15,000 $ 122.22 Granted 69,550 41.77 Vested (7,500 ) 122.22 Unvested shares at December 31, 2016 77,050 $ 49.60 Performance-based stock options During the years ended December 31, 2016, 2015 and 2014, no options to purchase shares of common stock that contain performance-based or a combination of performance-based and service-based vesting criteria were granted by the Company. However, certain performance-based stock options issued in prior periods were still outstanding as of December 31, 2016. Performance-based vesting criteria for options primarily relate to milestone events specific to the Company’s corporate goals, including but not limited to certain preclinical, clinical and regulatory 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 December 31, 2016, certain of the performance-based milestones had been achieved. The achievements of all remaining milestones have been deemed probable as of December 31, 2016 and therefore the related expense either has been fully recognized or is being recognized over the remaining service period. During the years ended December 31, 2016, 2015 and 2014, the Company recognized stock-based compensation expense of $0.9 million, $0.4 million and $0.9 million, respectively, related to stock options with performance-based vesting criteria. Performance-based stock units The Company may grant awards of performance stock units (“PSUs”) to non-employee The Company granted 114,503 PSUs and 100,270 PSUs during the years ended December 31, 2016 and 2015, respectively. Stock-based compensation expense associated with these PSUs is recognized if the performance condition is considered probable of achievement using management’s best estimates. As of December 31, 2016, these milestones were not probable and, therefore, no expense has been recognized related to these awards. No such awards were granted during the year ended December 31, 2014. The following table presents PSU activity for the year ended December 31, 2016: Number of Weighted-average Unvested shares at December 31, 2015 100,270 $ 64.44 Granted 114,503 45.02 Vested — — Forfeited/expired (14,160 ) 64.44 Unvested shares at December 31, 2016 200,613 $ 53.36 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 is 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 The Company recorded $0.8 million, $0.4 million and $0.1 million of stock-based compensation expense for the years ended December 31, 2016, 2015 and 2014, respectively, related to the 2013 ESPP. Stock-based compensation expense During the years ended December 31, 2016, 2015 and 2014, the Company recorded stock-based compensation expense for employee and non-employee Years Ended December 31, 2016 2015 2014 Research and development expense $ 25,386 $ 17,419 $ 6,688 General and administrative expense 16,700 14,544 4,818 $ 42,086 $ 31,963 $ 11,506 No related tax benefits were recognized for the years ended December 31, 2016, 2015 and 2014. 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, Years Ending December 31, 2016 2015 2014 Risk-free interest rate 1.42 % 1.71 % 1.83 % Expected dividend yield — — — Expected term (in years) 6.05 6.04 6.03 Expected volatility 72.84 % 69.62 % 78.61 % Risk-free rate The risk-free rate is based on the yield curve of U.S. Treasury securities with periods commensurate with the expected term of the options being valued. Dividends The Company has never paid, and does not anticipate paying, any cash dividends in the foreseeable future, and therefore uses an expected dividend yield of zero in the option-pricing model. Volatility Since the Company was privately held through July 2013, it alone does not have the relevant company-specific historical data to support its expected volatility. As such, the Company uses a weighted-average of expected volatility based on the volatilities of a representative group of publicly traded biopharmaceutical companies; this representative group also includes the Company. For purposes of identifying representative companies, the Company considered characteristics such as number of product candidates and their stages of product development, area of therapeutic focus, length of trading history, companies’ stage of life cycle, size, and relevant financial metrics. The expected volatility has been determined using a weighted-average of the historical volatilities of the representative group of companies for a period equal to the expected term of the option grant. The Company intends to continue to consistently apply this process using similar entities until a sufficient amount of historical information regarding the volatility of the Company’s own share price becomes available or until circumstances change, such that the identified entities are no longer representative companies. In the latter case, more suitable, similar entities whose share prices are publicly available would be utilized in the calculation. Expected term The Company uses the “simplified method” as prescribed by the Securities and Exchange Commission Staff Accounting Bulletin No. 107, Share Based Payments Forfeitures Forfeitures are required to be estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. The Company uses historical data to estimate pre-vesting

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes The domestic and foreign components of loss before income taxes are as follows, in thousands: Years ended December 31, 2016 2015 2014 Domestic $ (179,896 ) $ (111,057 ) $ (53,930 ) Foreign (18,575 ) (6,674 ) — Loss before income taxes $ (198,471 ) $ (117,731 ) $ (53,930 ) The provision (benefit) for income taxes is as follows for the years ended December 31, 2016, 2015 and 2014 (in thousands): Years Ended December 31, 2016 2015 2014 Current: Federal $ — $ — $ (444) State — — 18 Foreign — — — Total current — — (426 ) Deferred: Federal — — — State — — — Foreign — — — Total deferred — — — Total $ — $ — $ (426 ) A reconciliation of the expected income tax benefit (expense) computed using the federal statutory income tax rate to the Company’s effective income tax rate is as follows for the years ended December 31, 2016, 2015 and 2014: December 31, 2016 2015 2014 Income tax benefit computed at federal statutory tax rate 35.00% 35.00% 35.00% State taxes, net of federal benefit 2.90 4.50 4.90 Change in valuation allowance (43.40) (44.60) (35.80) General business credits and other credits 9.50 8.40 (1.90) Permanent differences (0.20) (0.20) (0.10) Incentive Stock Options (1.80) (1.80) (2.00) Foreign Rate Differential (1.90) (1.20) — Other (0.10) (0.10) 0.80 Total 0.00% 0.00% 0.90% Deferred income taxes reflect the net tax effects of temporary differences between the carrying amount of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of the Company’s deferred tax assets and liabilities for the years ended December 31, 2016 and 2015 are as follows (in thousands): December 31, 2016 2015 Deferred tax assets: Net operating loss carryforwards $ 126,077 $ 81,947 Deferred revenue 8,051 7,046 Tax credit carryforwards 43,350 16,708 Purchased intangible assets 4,410 724 Stock-based compensation 22,731 11,923 Deferred rent 8,516 7,975 Non-deductible 3,310 2,520 Total deferred tax assets 216,445 128,843 Valuation allowance (208,033) (121,874) Total deferred tax assets $ 8,412 $ 6,969 Deferred tax liabilities: Depreciation and amortization $ (8,412) $ (6,969) Total deferred tax liabilities $ (8,412) $ (6,969) Net deferred tax asset $ — $ — As of December 31, 2016, the Company had net operating loss carryforwards available (NOLs) to reduce federal, state and foreign income taxes of approximately $387.2 million, $391.5 million and $20.2 million, respectively. If not utilized, these carryforwards expire at various dates through 2036. At December 31, 2016, the Company also has available research and development tax credits for federal and state income tax purposes of approximately $7.3 million and $4.2 million, respectively. The Company engaged in clinical testing activities and incurred expenses that qualify for the federal orphan drug tax credit. At December 31, 2016, the Company has available orphan drug tax credits for federal purposes only of approximately $33.3 million. If not utilized, the credits expire at various dates through 2036. Included in the carryforwards above, the Company has federal and state NOLs related to stock compensation in the amount of $81.9 million and $77.8 million, respectively, which is not included in deferred tax assets. When the excess stock-based compensation related to the NOL carryover tax assets are realized, the benefit will be credited directly to stockholders’ equity under the Company’s current accounting policy. However, the Company will adopt ASU 2016-09, Improvements to Employee Share-Based Payment Accounting Utilization of the net operating loss carryforwards and credits may be subject to annual limitations as prescribed by federal and state statutory provisions. The annual limitation may result in the expiration of net operating loss carryforwards prior to its utilization. Utilization of the NOLs and tax credit carryforwards may be subject to a substantial annual limitation due to ownership change limitations that have occurred previously or that could occur in the future, as provided by Section 382 of the Internal Revenue Code of 1986 (“Section 382”), as well as similar state provisions. Ownership changes may limit the amount of NOLs and tax credit carryforwards that can be utilized annually to offset future taxable income and tax, respectively. In general, an ownership change, as defined by Section 382, results from transactions that increase the ownership of five percent stockholders in the stock of a corporation by more than 50 percent in the aggregate over a three-year period. During 2011, the Company completed a Section 382 study through December 31, 2011, to determine whether any ownership change has occurred since the Company’s formation and determined that transactions have resulted in two ownership changes, as defined by Section 382. The impact of the ownership changes have been reflected in the Company’s deferred tax assets in the table above. There could be additional ownership changes after December 31, 2011 that could further limit the amount of NOLs and tax credit carryforwards that the Company can utilize. The Company will complete a full analysis of the tax attribute carryforwards prior to any utilization. As required by ASC 740, management of the Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets. Based on the weight of available evidence, both positive and negative, management has recorded a valuation allowance of $208.0 million and $121.9 million at December 31, 2016 and December 31, 2015, respectively, because management has determined that it is more likely than not that these assets will not be fully realized. The valuation allowance increased by $86.1 million in the year ended December 31, 2016. 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 December 31, 2016 and 2015, the Company had no unrecognized tax benefits. The Company recognizes interest and penalties related to uncertain tax positions in income tax expense. The Company is subject to taxation in the United States and Switzerland. The statute of limitations for assessment by the Internal Revenue Service (IRS) and state tax authorities is open for tax years ending December 31, 2016, 2015, 2014, and 2013 although carryforward attributes that were generated for tax years prior to 2013 may still be adjusted upon examination by the IRS or state tax authorities if they either have been, or will be, used in a future period. The statute of limitations for assessment in Switzerland remains open for tax year ending December 31, 2016 and 2015. There are currently no federal, state or foreign audits in progress.

Defined Contribution Benefit Pl

Defined Contribution Benefit Plan	12 Months Ended
	Dec. 31, 2016
Compensation and Retirement Disclosure [Abstract]
Defined Contribution Benefit Plan	10. Defined Contribution Benefit Plan The Company sponsors a 401(k) retirement plan, in which substantially all of its full-time employees are eligible to participate. Participants may contribute a percentage of their annual compensation to this plan, subject to statutory limitations. The Company will make matching contributions equal to 50% of the employee’s contributions, subject to a maximum of 6% of eligible compensation. During the year ended December 31, 2016 and 2015, the Company provided $1.0 million and $0.7 million, respectively, in contributions to this plan. The Company did not provide any contributions during the year ended December 31, 2014.

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	11. Selected Quarterly Financial Data (Unaudited) 2016 First Second Third Fourth (In thousands, except per share data) Total revenue $ 31,281 $ 6,978 $ 8,985 $ 22,648 Loss from operations (23,594) (56,470) (63,512 ) (57,409) Net loss (23,198) (55,953) (62,834 ) (56,486) Net loss per share – basic and diluted (0.61) (1.47) (1.63 ) (1.34) 2015 First Second Third Fourth (In thousands, except per share data) Total revenue $ 34,202 $ 13,219 $ 5,480 $ 6,218 Loss from operations (5,195) (32,133) (40,475 ) (40,897) Net loss (4,957) (31,897) (40,257 ) (40,621) Net loss per share – basic and diluted (0.13) (0.85) (1.07 ) (1.08)

Summary of Significant Accoun21

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Principles of consolidation	Principles of consolidation The Company’s consolidated financial statements include the Company’s accounts and the accounts of the Company’s wholly owned subsidiaries, Agios Securities Corporation and Agios International Sarl. All intercompany transactions have been eliminated in consolidation. The consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles (“GAAP”).
Use of estimates	Use of estimates The preparation of financial statements in conformity with U.S. GAAP requires the Company’s management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances. Actual results could differ from those estimates.
Revenue recognition	Revenue recognition The Company recognizes revenue in accordance with the Financial Accounting Standards Board’s (“FASB”) Accounting Standards Codification (“ASC”) 605, Revenue Recognition • persuasive evidence of an arrangement exists; • delivery has occurred or services have been rendered; • the seller’s price to the buyer is fixed or determinable; and • collectability is reasonably assured. Collaboration Agreements with Celgene To date, the Company’s revenue has primarily been generated from its collaboration agreements with Celgene, a related party through ownership of the Company’s common stock, (collectively, “Collaboration Agreements”). In April 2010, the Company entered into a collaboration agreement focused on cancer metabolism. The agreement was amended in October 2011 and July 2014 (the agreement together with the amendments, the “2010 Agreement”). On April 27, 2015, the Company entered into a joint worldwide development and profit share collaboration and license agreements (collectively, the “AG-881 AG-881 AG-881 Collaboration and license revenue In January 2011, the Company adopted FASB Accounting Standards Update (“ASU”) No. 2009-13, Multiple-Element Revenue Arrangements (“ASU 2009-13”) , 605-25, In July 2014, the Company amended its 2010 Agreement. The amendment was determined to be a material modification pursuant to ASU 2009-13. 605-25, AG-881 605-25. Pursuant to ASC 605-25, • delivered item or items have value to the customer on a standalone basis, and • if the arrangement includes a general right of return relative to the delivered item or items, delivery or performance of the undelivered item or items is considered probable and substantially in the control of the vendor. If a deliverable meets both criteria above, it is considered a separate unit of accounting. If a deliverable does not meet both criteria above, it will be evaluated in combination with other deliverables and, if appropriate, aggregated to form one unit of accounting. The arrangement consideration is then allocated to each unit of accounting based on the relative selling price, using the Company’s best estimate of selling price of each unit of accounting, if vendor specific objective evidence or third party evidence is not available. The provisions of ASC 605-25 The Company recognizes revenue for the units of accounting over the term of the related contract or as undelivered items are delivered (proportional performance method), as appropriate. Under the proportional performance method, the consideration allocated to each unit of accounting is recognized as revenue based on the ratio of the level of effort incurred to date compared to the total estimated level of effort required to complete the Company’s performance obligations under the unit of accounting. Determining the total estimated level of effort required to complete all performance obligations requires management judgment and estimation, including assumptions regarding future operating performance, the timelines of the clinical trial approvals and the estimated patient populations. Reimbursement of research and development costs under the Company’s Collaboration Agreements are recognized as revenue, provided the Company has determined that it is acting primarily as a principal in the transaction according to the provisions outlined in FASB ASC 605-45, Revenue Recognition – Principal Agent Considerations 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. Milestone revenue The Company applies the provisions of ASC 605-28, Revenue Recognition – Milestone Method 605-28, Revenue from milestones, if they are nonrefundable and deemed substantive, are recognized upon achievement of the milestones. The Company recognizes revenue associated with non-substantive
Research and development costs	Research and development costs Research and development costs are expensed as incurred. Research and development costs include salaries and personnel-related costs, consulting fees, fees paid for contract research services, fees paid to clinical research organizations and other third parties associated with clinical trials, the costs of laboratory equipment and facilities, and other external costs. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are delivered or the services are performed.
Stock-based compensation	Stock-based compensation The Company accounts for its stock-based compensation awards in accordance with ASC 718, Compensation –Stock Compensation . Stock-based payments issued to non-employees Equity non-employees,
Income taxes	Income taxes Income taxes are recorded in accordance with ASC 740, Accounting for Income Taxes The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. The Company evaluated whether any uncertain tax positions arise from commencing operations of its wholly owned subsidiary, Agios International Sarl, and determined no uncertain tax positions existed. As of December 31, 2016 and 2015, the Company does not have any uncertain tax positions.
Comprehensive income (loss)	Comprehensive income (loss) Comprehensive income (loss) is defined as the change in equity of a business enterprise during a period from transactions, and other events and circumstances from non-owner available-for-sale available-for-sale
Cash and cash equivalents	Cash and cash equivalents The Company considers highly liquid investments with a maturity of three months or less when purchased to be cash equivalents. Cash equivalents, which consist primarily of money market funds and corporate debt securities, are stated at fair value.
Marketable securities	Marketable securities Marketable securities at December 31, 2016 and 2015 consisted primarily of investments in certificates of deposits, United States Treasuries, government securities and corporate debt securities. 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 Investments – Debt and Equity Securities 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 consolidated 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 December 31, 2016 consisted of the following (in thousands): Amortized Cost Unrealized Unrealized Fair Current: Certificates of deposit $ 11,280 $ 2 $ (3 ) $ 11,279 U.S. Treasuries 141,678 2 (62 ) 141,618 Government securities 19,533 — (23 ) 19,510 Corporate debt securities 208,285 3 (135 ) 208,153 Non-current: Certificates of deposit 7,600 6 (13 ) 7,593 Government securities 4,499 — (21 ) 4,478 Corporate debt securities 20,248 — (69 ) 20,179 $ 413,123 $ 13 $ (326 ) $ 412,810 Marketable securities at December 31, 2015 consisted of the following (in thousands): Amortized Unrealized Unrealized Fair Current: Certificates of deposit $ 11,248 $ — $ (5 ) $ 11,243 U.S. Treasuries 234,130 10 (145 ) 233,995 Non-current: U.S. Treasuries 59,083 — (178 ) 58,905 $ 304,461 $ 10 $ (328 ) $ 304,143 At December 31, 2016 and 2015, the Company held both current and non-current non-current available-for-sale. At December 31, 2016 and 2015, the Company held 158 and 74 debt securities, respectively, that were in an unrealized loss position. The aggregate fair value of debt securities in an unrealized loss position at December 31, 2016 and 2015 was $335.4 million and $207.4 million, respectively. There were no individual securities that were in a significant unrealized loss position or that had been in an unrealized loss position for greater than one year as of December 31, 2016 and 2015. 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 December 31, 2016 and 2015.
Concentrations of credit risk	Concentrations of credit risk Financial instruments which potentially subject the Company to credit risk consist primarily of cash, cash equivalents and marketable securities. The Company holds these investments in highly rated financial institutions, and, by policy, limits the amounts of credit exposure to any one financial institution. These amounts at times may exceed federally insured limits. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to any significant credit risk on these funds. The Company has no off-balance The Company is also subject to credit risk from its collaboration receivable. The Company evaluates the creditworthiness of its collaborator and has determined it is credit worthy. To date the Company has not experienced any losses with respect to its collaboration receivable.
Fair value measurements	Fair value measurements The Company records cash equivalents and marketable securities at fair value. ASC 820, Fair Value Measurements and Disclosures Level 1 – Level 2 – Level 3 – The following table summarizes the cash equivalents and marketable securities measured at fair value on a recurring basis as of December 31, 2016 (in thousands): Level 1 Level 2 Level 3 Total Cash equivalents $ 143,352 $ 7,897 $ — $ 151,249 Marketable securities: Certificates of deposit — 18,872 — 18,872 U.S. Treasuries 141,618 — — 141,618 Government securities 11,514 12,474 — 23,988 Corporate debt securities — 228,332 — 228,332 $ 296,484 $ 267,575 $ — $ 564,059 The following table summarizes the cash equivalents and marketable securities measured at fair value on a recurring basis as of December 31, 2015 (in thousands): Level 1 Level 2 Level 3 Total Cash equivalents $ 59,332 $ — $ — $ 59,332 Marketable securities: Certificates of deposit — 11,243 — 11,243 U.S. Treasuries 292,900 — — 292,900 $ 352,232 $ 11,243 $ — $ 363,475 Cash equivalents and marketable securities have been initially valued at the transaction price and subsequently revalued, 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. After completing its validation procedures, the Company did not adjust or override any fair value measurements provided by the pricing services as of December 31, 2016 or 2015. There have been no changes to the valuation methods during the years ended December 31, 2016 and 2015. The Company evaluates transfers between levels at the end of each reporting period. Due to the lack of an active market, the Company transferred $11.0 million of government securities from Level 1 to Level 2 during the year ended December 31, 2016. There were no transfers of assets or liabilities between Level 1 and Level 2 during the year ended December 31, 2015. The Company had no financial assets or liabilities that were classified as Level 3 at any point during the years ended December 31, 2016 and 2015. Due to their short-term nature, the carrying amounts reflected in the consolidated balance sheets for cash, collaboration receivable – related party, tenant improvement and other receivables, prepaid expenses and other current and non-current
Collaboration and other receivables	Collaboration and other receivables Collaboration receivables as of December 31, 2016 and 2015 represent amounts due under our Collaboration Agreements for reimbursements of certain costs. Other receivables represent amounts due from the Company’s landlord for reimbursement of tenant improvements under the Company’s lease agreement. The Company estimates an allowance for doubtful accounts based on credit worthiness, historical payment patterns, aging of accounts receivable balances, and general economic conditions. As of December 31, 2016 and 2015, the Company had no allowance for doubtful accounts.
Property and equipment	Property and equipment Property and equipment consist of laboratory equipment, computer equipment and software, leasehold improvements, furniture and fixtures, and office equipment. Property and equipment is stated at cost, and depreciated using the straight-line method over the estimated useful lives of the respective assets: Laboratory equipment 5 years Computer equipment and software 3 years Leasehold improvements Shorter of asset’s useful life or remaining term of lease Furniture and fixtures 5 years Office equipment 5 years Costs of major additions and betterments are capitalized; maintenance and repairs, which do not improve or extend the life of the respective assets, are charged to expense as incurred. Upon retirement or sale, the cost of the disposed asset and the related accumulated depreciation are removed from the accounts and the resulting gain or loss is recognized.
Impairment of long-lived assets	Impairment of long-lived assets The Company periodically evaluates its long-lived assets for potential impairment in accordance with ASC 360, Property, Plant and Equipment
Segment and geographic information	Segment and geographic information Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker, or decision-making group, in making decisions on how to allocate resources and assess performance. The Company’s chief operating decision maker is the chief executive officer. The Company and the chief operating decision maker view the Company’s operations and manage its business as one operating segment.
Net loss per share applicable to common stockholders	Net loss per share Basic net loss per share is calculated by dividing net loss by the weighted-average shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share 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 the dilutive net loss per share calculation, stock options, including performance-based stock options which were determined to be probable of achievement, restricted stock units, unvested restricted stock and employee stock purchase plan shares are considered to be common stock equivalents but are excluded from the calculation of diluted net loss per share as their effect would be anti-dilutive. Since the Company had a net loss for all periods presented, the effect of all potentially dilutive securities is anti-dilutive. Accordingly, basic and diluted net loss per share was the same for the years ended December 31, 2016, 2015 and 2014. Furthermore, 323,339 performance-based stock options and stock units that were previously granted had not vested as of December 31, 2016 and were excluded from diluted shares outstanding as the vesting conditions for the awards, discussed further in Note 8 “Share-Based Payments,” had not been met as of December 31, 2016. The following common stock equivalents were excluded from the calculation of diluted net loss per share applicable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: Years ended December 31, 2016 2015 2014 Stock options 5,218,880 4,618,697 3,795,420 Restricted stock units 77,050 15,000 10,000 Unvested restricted stock — — 8,522 Employee stock purchase plan shares 24,018 7,721 7,159 5,319,948 4,641,418 3,821,101
Recent accounting pronouncements	Recent accounting pronouncements Revenue from Contracts with Customers In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) 2014-09”). 2015-14, Revenue from Contracts with Customers (Topic 606) 2014-09; No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net) 2014-09; No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing 2014-09; No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients 2014-09 The Revenue ASUs provide an accounting standard 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, 2017, with an option to early adopt for interim and annual periods beginning after December 15, 2016. The guidance permits two methods of adoption: retrospectively to each prior reporting period presented (the full retrospective method), or retrospectively with the cumulative effect of initially applying the guidance recognized at the date of initial application (the modified retrospective method). We currently anticipate adoption of the new standard effective January 1, 2018 under the modified retrospective method. The Company is in the process of determining the impact of the Revenue ASUs on its financial statements; however, the adoption of the Revenue ASUs is expected to have a significant impact on the Company’s notes to consolidated financial statements and its internal controls over financial reporting. Other Recent Accounting Pronouncements In October, 2016, the FASB issued ASU No. 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory 2016-16”), 2016-16 In March 2016, the FASB issued ASU No. 2016-09, Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting 2016-09”), 2016-09 In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) 2016-02”), 2016-02 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.
Subsequent events	Subsequent events The Company considered events or transactions occurring after the balance sheet date, but prior to the issuance of the consolidated financial statements, for potential recognition or disclosure in its consolidated financial statements. All significant subsequent events have been properly disclosed in the consolidated financial statements.

Summary of Significant Accoun22

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Marketable Securities	Marketable securities at December 31, 2016 consisted of the following (in thousands): Amortized Cost Unrealized Unrealized Fair Current: Certificates of deposit $ 11,280 $ 2 $ (3 ) $ 11,279 U.S. Treasuries 141,678 2 (62 ) 141,618 Government securities 19,533 — (23 ) 19,510 Corporate debt securities 208,285 3 (135 ) 208,153 Non-current: Certificates of deposit 7,600 6 (13 ) 7,593 Government securities 4,499 — (21 ) 4,478 Corporate debt securities 20,248 — (69 ) 20,179 $ 413,123 $ 13 $ (326 ) $ 412,810 Marketable securities at December 31, 2015 consisted of the following (in thousands): Amortized Unrealized Unrealized Fair Current: Certificates of deposit $ 11,248 $ — $ (5 ) $ 11,243 U.S. Treasuries 234,130 10 (145 ) 233,995 Non-current: U.S. Treasuries 59,083 — (178 ) 58,905 $ 304,461 $ 10 $ (328 ) $ 304,143
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 December 31, 2016 (in thousands): Level 1 Level 2 Level 3 Total Cash equivalents $ 143,352 $ 7,897 $ — $ 151,249 Marketable securities: Certificates of deposit — 18,872 — 18,872 U.S. Treasuries 141,618 — — 141,618 Government securities 11,514 12,474 — 23,988 Corporate debt securities — 228,332 — 228,332 $ 296,484 $ 267,575 $ — $ 564,059 The following table summarizes the cash equivalents and marketable securities measured at fair value on a recurring basis as of December 31, 2015 (in thousands): Level 1 Level 2 Level 3 Total Cash equivalents $ 59,332 $ — $ — $ 59,332 Marketable securities: Certificates of deposit — 11,243 — 11,243 U.S. Treasuries 292,900 — — 292,900 $ 352,232 $ 11,243 $ — $ 363,475
Estimated Useful Lives of Property and Equipment	Property and equipment is stated at cost, and depreciated using the straight-line method over the estimated useful lives of the respective assets: Laboratory equipment 5 years Computer equipment and software 3 years Leasehold improvements Shorter of asset’s useful life or remaining term of lease Furniture and fixtures 5 years Office equipment 5 years
Common Stock Excluded from Calculation of Diluted Net Loss Per Share	The following common stock equivalents were excluded from the calculation of diluted net loss per share applicable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: Years ended December 31, 2016 2015 2014 Stock options 5,218,880 4,618,697 3,795,420 Restricted stock units 77,050 15,000 10,000 Unvested restricted stock — — 8,522 Employee stock purchase plan shares 24,018 7,721 7,159 5,319,948 4,641,418 3,821,101

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Summary of Property and Equipment	Property and equipment consists of the following (in thousands): December 31, 2016 2015 Laboratory equipment $ 14,529 $ 9,751 Computer equipment and software 3,204 2,029 Leasehold improvements 19,858 15,853 Furniture and fixtures 748 413 Office equipment 233 206 Construction in progress 137 2,632 Total property and equipment 38,709 30,884 Less accumulated depreciation (13,372 ) (7,664 ) Total property and equipment, net $ 25,337 $ 23,220

Accrued Expenses and Other Cu24

Accrued Expenses and Other Current Liabilities (Tables)	12 Months Ended
	Dec. 31, 2016
Payables and Accruals [Abstract]
Summary of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consist of the following (in thousands): December 31, 2016 2015 Accrued compensation $ 11,092 $ 7,005 Accrued contracted research and development costs 20,266 7,449 Accrued professional fees 476 228 Accrued other 168 1,314 Total $ 32,002 $ 15,996

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Summary of Future Annual Minimum Lease Payments Due Under Operating Leases	Future annual minimum lease payments due under non-cancellable 2017 $ 9,050 2018 9,278 2019 9,511 2020 9,751 2021 9,996 Thereafter 3,903 $ 51,489

Share-Based Payments (Tables)

Share-Based Payments (Tables)	12 Months Ended
	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Company's Stock Option Activity of all Stock Incentive Plans	The following table summarizes the stock option activity of all stock incentive plans for the year ended December 31, 2016. Number of Weighted- Weighted- Aggregate Outstanding at December 31, 2015 4,618,697 $ 44.45 7.49 $ 153,573 Granted 1,556,240 43.99 Exercised (603,359 ) 10.84 Forfeited/Expired (352,698 ) 65.21 Outstanding at December 31, 2016 5,218,880 $ 46.79 7.28 $ 63,559 Exercisable at December 31, 2016 2,527,605 $ 36.50 5.85 $ 53,952 Vested and expected to vest at December 31, 2016 5,065,064 $ 46.43 7.23 $ 63,351
Unvested Stock Unit Activity	The following table presents RSU activity for the year ended December 31, 2016: Number of Weighted-average Unvested shares at December 31, 2015 15,000 $ 122.22 Granted 69,550 41.77 Vested (7,500 ) 122.22 Unvested shares at December 31, 2016 77,050 $ 49.60
Schedule of Performance-Based Units	The following table presents PSU activity for the year ended December 31, 2016: Number of Weighted-average Unvested shares at December 31, 2015 100,270 $ 64.44 Granted 114,503 45.02 Vested — — Forfeited/expired (14,160 ) 64.44 Unvested shares at December 31, 2016 200,613 $ 53.36
Stock-Based Compensation Expense for Employee and Non-Employee Stock Options, Restricted Stock Units, Performance-Based Stock Options, Performance-Based Stock Units and Employee Stock Purchase Plan Shares	During the years ended December 31, 2016, 2015 and 2014, the Company recorded stock-based compensation expense for employee and non-employee Years Ended December 31, 2016 2015 2014 Research and development expense $ 25,386 $ 17,419 $ 6,688 General and administrative expense 16,700 14,544 4,818 $ 42,086 $ 31,963 $ 11,506
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: Years Ending December 31, 2016 2015 2014 Risk-free interest rate 1.42 % 1.71 % 1.83 % Expected dividend yield — — — Expected term (in years) 6.05 6.04 6.03 Expected volatility 72.84 % 69.62 % 78.61 %

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Schedule of Domestic and Foreign Components of Loss Before Income Taxes	The domestic and foreign components of loss before income taxes are as follows, in thousands: Years ended December 31, 2016 2015 2014 Domestic $ (179,896 ) $ (111,057 ) $ (53,930 ) Foreign (18,575 ) (6,674 ) — Loss before income taxes $ (198,471 ) $ (117,731 ) $ (53,930 )
Provision (Benefit) for Income Taxes	The provision (benefit) for income taxes is as follows for the years ended December 31, 2016, 2015 and 2014 (in thousands): Years Ended December 31, 2016 2015 2014 Current: Federal $ — $ — $ (444) State — — 18 Foreign — — — Total current — — (426 ) Deferred: Federal — — — State — — — Foreign — — — Total deferred — — — Total $ — $ — $ (426 )
Reconciliation of Expected Income Tax Benefit (Expense) Computed Using Federal Statutory Income Tax Rate	A reconciliation of the expected income tax benefit (expense) computed using the federal statutory income tax rate to the Company’s effective income tax rate is as follows for the years ended December 31, 2016, 2015 and 2014: December 31, 2016 2015 2014 Income tax benefit computed at federal statutory tax rate 35.00% 35.00% 35.00% State taxes, net of federal benefit 2.90 4.50 4.90 Change in valuation allowance (43.40) (44.60) (35.80) General business credits and other credits 9.50 8.40 (1.90) Permanent differences (0.20) (0.20) (0.10) Incentive Stock Options (1.80) (1.80) (2.00) Foreign Rate Differential (1.90) (1.20) — Other (0.10) (0.10) 0.80 Total 0.00% 0.00% 0.90%
Company's Deferred Tax Assets and Liabilities	Significant components of the Company’s deferred tax assets and liabilities for the years ended December 31, 2016 and 2015 are as follows (in thousands): December 31, 2016 2015 Deferred tax assets: Net operating loss carryforwards $ 126,077 $ 81,947 Deferred revenue 8,051 7,046 Tax credit carryforwards 43,350 16,708 Purchased intangible assets 4,410 724 Stock-based compensation 22,731 11,923 Deferred rent 8,516 7,975 Non-deductible 3,310 2,520 Total deferred tax assets 216,445 128,843 Valuation allowance (208,033) (121,874) Total deferred tax assets $ 8,412 $ 6,969 Deferred tax liabilities: Depreciation and amortization $ (8,412) $ (6,969) Total deferred tax liabilities $ (8,412) $ (6,969) Net deferred tax asset $ — $ —

Selected Quarterly Financial 28

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Summary of Quarterly Financial Data	2016 First Second Third Fourth (In thousands, except per share data) Total revenue $ 31,281 $ 6,978 $ 8,985 $ 22,648 Loss from operations (23,594) (56,470) (63,512 ) (57,409) Net loss (23,198) (55,953) (62,834 ) (56,486) Net loss per share – basic and diluted (0.61) (1.47) (1.63 ) (1.34) 2015 First Second Third Fourth (In thousands, except per share data) Total revenue $ 34,202 $ 13,219 $ 5,480 $ 6,218 Loss from operations (5,195) (32,133) (40,475 ) (40,897) Net loss (4,957) (31,897) (40,257 ) (40,621) Net loss per share – basic and diluted (0.13) (0.85) (1.07 ) (1.08)

Nature of Business - Additional

Nature of Business - Additional Information (Detail) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Sep. 30, 2016USD ($)$ / sharesshares	Dec. 31, 2016USD ($)Diseases	Dec. 31, 2014USD ($)	Dec. 31, 2015USD ($)
Basis Of Presentation [Line Items]
Accumulated deficit		$ (483,151)		$ (284,680)
Net proceeds from public offering		162,150	$ 333,577
Cash, cash equivalents and marketable securities		$ 573,600
Public Offering [Member]
Basis Of Presentation [Line Items]
Number of shares issued from public offering | shares	3,370,786
Public offering price per share | $ / shares	$ 44.50
Net proceeds from public offering	$ 141,000
Underwriters Public Offering [Member]
Basis Of Presentation [Line Items]
Number of shares issued from public offering | shares	505,617
Net proceeds from public offering	$ 21,100
Minimum [Member]
Basis Of Presentation [Line Items]
Number of rare genetic disease under entity therapeutic group | Diseases		600

Summary of Significant Accoun30

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016USD ($)SecuritiesSegmentshares	Dec. 31, 2015USD ($)Securities
Significant Of Accounting Policies [Line Items]
Unrecognized tax benefits	$ 0	$ 0
Realized gains or losses on marketable securities	$ 0
Minimum period to liquidate	12 months	12 months
Debt securities in an unrealized loss position | Securities	158	74
Aggregate fair value of debt securities in an unrealized loss position	$ 335,400,000	$ 207,400,000
Concentration of credit risk	The Company has not experienced any credit losses in such accounts and does not believe it is exposed to any significant credit risk on these funds.
Off- balance sheet concentrations of credit risk	The Company has no off-balance sheet concentrations of credit risk, such as foreign currency exchange contracts, option contracts or other hedging arrangements.
Financial assets or liabilities that were classified as Level 3	$ 0	0
Transfers of assets from Level 1 to Level 2		0
Transfers of assets from Level 2 to Level 1		0
Transfers of liabilities from Level 1 to Level 2		0
Transfers of liabilities from Level 2 to Level 1		0
Number of operating segments | Segment	1
Stock options granted | shares	1,556,240
Government Securities [Member]
Significant Of Accounting Policies [Line Items]
Transfers of assets from Level 1 to Level 2	$ 11,000,000
Performance-Based Stock Option Grants [Member]
Significant Of Accounting Policies [Line Items]
Stock options granted | shares	323,339
Level 3 [Member]
Significant Of Accounting Policies [Line Items]
Financial assets classified as Level 3	$ 0	0
Financial liabilities classified as Level 3	$ 0	$ 0
Maximum [Member]
Significant Of Accounting Policies [Line Items]
Investment maturity period, non-current	2 years	2 years
Investment maturity period, current	1 year	1 year
Minimum [Member]
Significant Of Accounting Policies [Line Items]
Investment maturity period, non-current	1 year	1 year

Summary of Significant Accoun31

Summary of Significant Accounting Policies - Marketable Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Fair Value	$ 564,059	$ 363,475
Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	18,872	11,243
U.S. Treasuries [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	141,618	292,900
Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	23,988
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	228,332
Fair Value, Measurements, Recurring [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	413,123	304,461
Unrealized Gains	13	10
Unrealized Losses	(326)	(328)
Fair Value	412,810	304,143
Fair Value, Measurements, Recurring [Member] | Current: [Member] | Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,280	11,248
Unrealized Gains	2
Unrealized Losses	(3)	(5)
Fair Value	11,279	11,243
Fair Value, Measurements, Recurring [Member] | Current: [Member] | U.S. Treasuries [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	141,678	234,130
Unrealized Gains	2	10
Unrealized Losses	(62)	(145)
Fair Value	141,618	233,995
Fair Value, Measurements, Recurring [Member] | Current: [Member] | Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19,533
Unrealized Losses	(23)
Fair Value	19,510
Fair Value, Measurements, Recurring [Member] | Current: [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	208,285
Unrealized Gains	3
Unrealized Losses	(135)
Fair Value	208,153
Fair Value, Measurements, Recurring [Member] | Non-Current: [Member] | Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,600
Unrealized Gains	6
Unrealized Losses	(13)
Fair Value	7,593
Fair Value, Measurements, Recurring [Member] | Non-Current: [Member] | U.S. Treasuries [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		59,083
Unrealized Losses		(178)
Fair Value		$ 58,905
Fair Value, Measurements, Recurring [Member] | Non-Current: [Member] | Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,499
Unrealized Losses	(21)
Fair Value	4,478
Fair Value, Measurements, Recurring [Member] | Non-Current: [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	20,248
Unrealized Losses	(69)
Fair Value	$ 20,179

Summary of Significant Accoun32

Summary of Significant Accounting Policies - Cash Equivalents and Marketable Securities Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	$ 151,249	$ 59,332
Cash equivalents and marketable securities, total	564,059	363,475
Certificates of Deposit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents and marketable securities, total	18,872	11,243
U.S. Treasuries [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents and marketable securities, total	141,618	292,900
Government Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents and marketable securities, total	23,988
Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents and marketable securities, total	228,332
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	143,352	59,332
Cash equivalents and marketable securities, total	296,484	352,232
Level 1 [Member] | U.S. Treasuries [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents and marketable securities, total	141,618	292,900
Level 1 [Member] | Government Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents and marketable securities, total	11,514
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	7,897
Cash equivalents and marketable securities, total	267,575	11,243
Level 2 [Member] | Certificates of Deposit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents and marketable securities, total	18,872	$ 11,243
Level 2 [Member] | Government Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents and marketable securities, total	12,474
Level 2 [Member] | Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents and marketable securities, total	$ 228,332

Summary of Significant Accoun33

Summary of Significant Accounting Policies - Estimated Useful Lives of Property and Equipment (Detail)	12 Months Ended
	Dec. 31, 2016
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment useful life	5 years
Computer Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment useful life	3 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment useful life description	Shorter of asset's useful life or remaining term of lease
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment useful life	5 years
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment useful life	5 years

Summary of Significant Accoun34

Summary of Significant Accounting Policies - Common Stock Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	5,319,948	4,641,418	3,821,101
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	5,218,880	4,618,697	3,795,420
Restricted Stock Units (RSUs) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	77,050	15,000	10,000
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share			8,522
Employee Stock Purchase Plan shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	24,018	7,721	7,159

Celgene Collaboration Agreeme35

Celgene Collaboration Agreements - Additional Information (Detail)	May 17, 2016USD ($)	Apr. 27, 2015USD ($)	Apr. 27, 2015USD ($)	Jul. 31, 2014USD ($)	Jul. 31, 2014	Oct. 31, 2011	Dec. 31, 2016USD ($)$ / sharesshares	Mar. 31, 2016USD ($)	Mar. 31, 2015USD ($)$ / shares	Apr. 27, 2015USD ($)	May 17, 2016USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2016USD ($)$ / sharesshares	Jul. 31, 2014USD ($)	Dec. 31, 2015USD ($)shares	Dec. 31, 2016USD ($)Program$ / sharesshares	Dec. 31, 2015USD ($)shares	Dec. 31, 2014USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone or royalty payments received								$ 25,000,000								$ 0	$ 0	$ 0
Preferred stock, shares issued | shares							0						0		0	0	0
Collaboration revenue recognized																$ 44,900,000	$ 59,100,000	$ 65,400,000
Amended collaboration expiration date																		2016-04
Term of the initial discovery period before amendment to extend																		5 years
Term of extended period after amendment of the initial discovery period																		6 years
Payment made in pursuant to the amendment																		$ 20,000,000
Recognized revenue to extension			$ 700,000
Collaboration revenue recognized																69,892,000	59,119,000	65,358,000
Reduction of research and development costs																19,714,000	25,173,000	0
Collaboration receivable							$ 4,886,000						$ 4,886,000		$ 8,225,000	$ 4,886,000	8,225,000
2016 Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research agreement commence date																May 17, 2016
AG-881 Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial payment received		$ 10,000,000														$ 10,000,000
Revenue recognition, selling price													0			48,700,000
Collaboration revenue recognized											$ 89,000		92,000		100,000
AG-881 Agreements [Member] | Split License [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognition, selling price		33,200,000
Collaboration revenue recognized											1,400,000				12,000,000
AG-881 Agreements [Member] | Participation Service [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognition, selling price	$ 1,500,000	800,000
AG-881 Agreements [Member] | In Process Research and Development [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognition, selling price	$ 207,000,000	30,500,000
Collaboration revenue recognized											4,600,000		14,400,000		7,600,000
2010 Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone or royalty payments received																$ 0
Agreement amended date					2014-07	2011-10
Collaboration revenue recognized										$ 400,000
Collaboration revenue recognized									$ 5,100,000
Reduction in research and development expenditure									3,800,000	900,000
Reduction in net loss									$ 8,900,000
Decrease in net loss per share | $ / shares									$ (0.24)
2010 Agreement [Member] | In Process Research and Development [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognition, selling price														$ 42,700,000
July 2014 - April 2015 [Member] | Split License [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognition, selling price				$ 21,200,000
Collaboration revenue recognized										15,800,000
July 2014 - April 2015 [Member] | Participation Service [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognition, selling price				200,000
Collaboration revenue recognized										100,000		$ 100,000
July 2014 - April 2015 [Member] | In Process Research and Development [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognition, selling price				13,600,000
Collaboration revenue recognized										5,000,000		5,200,000
Celgene Collaboration Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue recognized							10,800,000
Reduction in research and development expenditure											900,000		1,000,000		3,000,000
Reduction in net loss							$ 10,800,000
Decrease in net loss per share | $ / shares																$ (0.28)
Additional reimbursable development expenses													200,000
Phase 1b Frontline Combination Trial [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue recognized											1,200,000						1,000,000
Reduction in research and development expenditure											300,000						$ 100,000
AG-120 And AG-881 Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Additional reimbursable development expenses											4,400,000
Other Than 65/35 Program [Member] | Co-Development and Co-Commercialization Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Profit or loss share percentage	50.00%
Other Than 65/35 Program [Member] | Co-Development and Co-Commercialization Agreements [Member] | Clinical Development Event [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone or royalty payments received	$ 20,000,000
Phase 1 [Member] | July 2014 - April 2015 [Member] | In Process Research and Development [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognition, selling price				$ 50,800,000
Collaboration revenue recognized										14,700,000		17,400,000
Prior to July 2014 Amendment [Member] | Scenario, Previously Reported [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of years company expected to fulfill its performance obligations																6 years
Four Separate Ongoing Development Services Determined as Primary Obligor of Development Activities [Member] | AG-881 Agreements [Member] | In Process Research and Development [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognition, selling price		12,700,000
Collaboration revenue recognized											1,700,000				1,700,000
Four Separate Ongoing Development Services Not Determined As Primary Obligor Of Development Activities [Member] | AG-881 Agreements [Member] | In Process Research and Development [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognition, selling price		97,300,000
Reduction in research and development expenditure											7,500,000				$ 17,100,000
Three Separate Ongoing Development Services Determined As Primary Obligor Of Development Activities [Member] | AG-881 Agreements [Member] | In Process Research and Development [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognition, selling price	67,800,000
Collaboration revenue recognized													21,300,000
Three Separate Ongoing Development Services Not Determined As Primary Obligor Of Development Activities [Member] | AG-881 Agreements [Member] | In Process Research and Development [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognition, selling price	22,400,000
Reduction in research and development expenditure													$ 5,700,000
Series B Convertible Preferred Stock [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial payment received																$ 121,200,000
Series B convertible preferred stock price per share | $ / shares							$ 1.70						$ 1.70			$ 1.70
Net proceeds of Series B convertible preferred stock																$ 8,800,000
Additional consideration under agreement																$ 3,100,000
Celgene [Member] | 2016 Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial research agreement period																4 years
Research agreement expire period																May 17, 2020
Term of research extended																2 years
Number of research programs | Program																3
Initial payment received	200,000,000
Upfront payment agreement extension fee receivable	40,000,000
Designation fee receivable	8,000,000
Option exercise fee receivable	30,000,000										30,000,000
Additional option exercise fee for further development	10,000,000
Celgene [Member] | Co-Development and Co-Commercialization Agreements [Member] | Clinical Development Event [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone or royalty payments received	25,000,000
Celgene [Member] | Co Commercial Agreement [Member] | Clinical Development Event [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone or royalty payments received	$ 25,000,000
Celgene [Member] | 65/35 Program [Member] | Co-Development and Co-Commercialization Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Profit or loss share percentage	65.00%
Celgene [Member] | Series B Convertible Preferred Stock [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Preferred stock, shares issued | shares							5,190,551						5,190,551			5,190,551
Minimum [Member] | Celgene [Member] | 2016 Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Minimum option exercise fee receivable for continuation program	$ 35,000,000										$ 35,000,000
Maximum [Member] | Co-Development and Co-Commercialization Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone or royalty payments received	168,800,000
Maximum [Member] | AG-881 Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Receipts of potential milestone payments		70,000,000	70,000,000							70,000,000
Milestone payment for filing of first NDA		15,000,000	15,000,000							15,000,000
Milestone payments upon achievement of specified regulatory milestone events		$ 55,000,000	$ 55,000,000							$ 55,000,000
Maximum [Member] | 2010 Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Receipts of potential milestone payments							$ 120,000,000						$ 120,000,000			$ 120,000,000
Milestone payments upon achievement of specified regulatory milestone events							70,000,000					$ 70,000,000	70,000,000			70,000,000		$ 70,000,000
Milestone payment upon achievement of a specified clinical development milestone event							25,000,000						25,000,000			25,000,000
Milestone payment upon achievement of a specified commercial milestone event							$ 25,000,000						$ 25,000,000			$ 25,000,000
Maximum [Member] | Other Than 65/35 Program [Member] | Co-Development and Co-Commercialization Agreements [Member] | Regulatory Milestone Events [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone or royalty payments received	148,800,000
Maximum [Member] | Celgene [Member] | Co-Development and Co-Commercialization Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone or royalty payments received	208,800,000
Maximum [Member] | Celgene [Member] | Co-Development and Co-Commercialization Agreements [Member] | Regulatory Milestone Events [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone or royalty payments received	183,800,000
Maximum [Member] | Celgene [Member] | Co Commercial Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone or royalty payments received	386,300,000
Maximum [Member] | Celgene [Member] | Co Commercial Agreement [Member] | Regulatory Milestone Events [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone or royalty payments received	236,300,000
Maximum [Member] | Celgene [Member] | Co Commercial Agreement [Member] | Commercial Milestone Events [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone or royalty payments received	$ 125,000,000

Property and Equipment - Summar

Property and Equipment - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 38,709	$ 30,884
Less accumulated depreciation	(13,372)	(7,664)
Total property and equipment, net	25,337	23,220
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	14,529	9,751
Computer Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	3,204	2,029
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	19,858	15,853
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	748	413
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	233	206
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 137	$ 2,632

Property and Equipment - Additi

Property and Equipment - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 5,708	$ 3,342	$ 1,367

Accrued Expenses and Other Cu38

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Payables and Accruals [Abstract]
Accrued compensation	$ 11,092	$ 7,005
Accrued contracted research and development costs	20,266	7,449
Accrued professional fees	476	228
Accrued other	168	1,314
Total	$ 32,002	$ 15,996

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016USD ($)Lawsuits	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Jul. 20, 2015ft²	Nov. 21, 2014ft²	Sep. 15, 2014ft²
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Operating lease | ft²					113,200	74,500
Lease agreement tenant incentive	$ 20,500,000
Stand by letter of credit	2,900,000
Tenant improvement allowance	3,100,000	$ 3,400,000
Rent expense	6,000,000	7,100,000	$ 3,700,000
Accruals from milestones achieved	220,163,000	141,827,000	100,371,000
License agreements amount	$ 70,000	135,000	83,000
Royalty payment		0
Milestone payment period	5 years
Contract term	5 years
Number of days for election	30 days
Period under contract term to declare development candidate for milestone Payments forgo	3 years
Legal proceedings | Lawsuits	0
Minimum [Member]
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Range related to royalties amount	0.50%
Range related to non royalties amount	7.00%
Maximum [Member]
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Range related to royalties amount	2.50%
Range related to non royalties amount	25.00%
Accrued Income Receivable [Member]
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Accruals from milestones achieved	$ 4,100,000
License Agreement Terms [Member]
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Accruals from milestones achieved	70,000	53,000
Payment of patent related to licensor	100,000
Payment of clinical development related to licensor	1,600,000
Regulatory payment related to licensor	5,400,000
Sales based payment related to licensor	$ 3,700,000
Patent-related milestone expense		$ 0	$ 50,000
Option to renew licenses	Option to renew these licenses on an annual basis in exchange for payments approximating $70,000 for 2017
License Agreement Terms [Member] | Clinical Milestones [Member]
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Accruals from milestones achieved	$ 500,000
License Agreement Terms [Member] | Patent Milestones [Member]
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Accruals from milestones achieved	$ 75,000
Preexisting Leases [Member]
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Operating lease | ft²						38,500
38 Sidney Street Lease Arrangement [Member]
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Lease termination date	Jun. 15, 2015
88 Sidney Street Lease Arrangement [Member]
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Operating lease | ft²				146,030
Lease termination date	May 15, 2022

Commitments and Contingencies40

Commitments and Contingencies - Future Annual Minimum Lease Payments Due Under Operating Leases (Detail) $ in Thousands	Dec. 31, 2016USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,017	$ 9,050
2,018	9,278
2,019	9,511
2,020	9,751
2,021	9,996
Thereafter	3,903
Total minimum lease payments	$ 51,489

Common Stock - Additional Infor

Common Stock - Additional Information (Detail)	Dec. 31, 2016USD ($)
Equity [Abstract]
Dividends declared or paid since the Company's inception	$ 0

Share-Based Payments - Addition

Share-Based Payments - Additional Information (Detail) - USD ($)	Jan. 01, 2017	Jan. 01, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Based compensation expense			$ 42,086,000	$ 31,963,000	$ 11,506,000
Stock options granted			1,556,240
Tax benefits related to stock based compensation			$ 0	$ 0	$ 0
Expected contractual term			10 years
Performance-Based Stock Option Grants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted			323,339
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense related to stock option			$ 2,100,000
Weighted-average period to recognize compensation expense			1 year 1 month 6 days
Fair value granted amount			69,550	15,000	10,000
Stock Based compensation expense			$ 2,000,000	$ 900,000	$ 100,000
Consultants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted			0	0	0
Advisors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted			0	0	0
Performance-Based Stock Units (PSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value granted amount			114,503
2007 Plan and 2013 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance			6,256,099
Shares available for future issuance			759,556
2013 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for issuance		1,507,860
Weighted-average grant date fair value of options			$ 28.41	$ 65.38	$ 27.26
Intrinsic value of options exercised			$ 26,400,000	$ 50,900,000	$ 60,400,000
Unrecognized compensation expense related to stock option			$ 81,700,000
Weighted-average period to recognize compensation expense			2 years 6 months
2013 Stock Incentive Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock			2,000,000
Common stock outstanding			4.00%
2013 Stock Incentive Plan [Member] | Performance-Based Stock Option Grants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense related to stock option			$ 11,600,000
Stock Based compensation expense			$ 900,000	$ 400,000	$ 900,000
Stock options granted			0	0	0
2013 Stock Incentive Plan [Member] | Performance-Based Stock Units (PSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Based compensation expense			$ 0
Stock options granted			114,503	100,270	0
2013 Stock Incentive Plan [Member] | Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for issuance	1,688,817
2013 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance			273,442
Stock Based compensation expense			$ 800,000	$ 400,000	$ 100,000
Common stock, shares issued			$ 36,680	$ 17,150	$ 0
Purchase price discount rate stock option			85.00%
Opportunity to purchase of common stock			327,272

Share-Based Payments - Summary

Share-Based Payments - Summary of Company's Stock Option Activity of all Stock Incentive Plans (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Number of Stock Options, Outstanding, Beginning balance	4,618,697
Number of Stock Options, Granted	1,556,240
Number of Stock Options, Exercised	(603,359)
Number of Stock Options, Forfeited/Expired	(352,698)
Number of Stock Options, Outstanding, Ending balance	5,218,880	4,618,697
Number of Stock Options, Exercisable	2,527,605
Number of Stock Options, Vested and expected to vest	5,065,064
Weighted-Average Exercise Price, Outstanding, Beginning balance	$ 44.45
Weighted-Average Exercise Price, Granted	43.99
Weighted-Average Exercise Price, Exercised	10.84
Weighted-Average Exercise Price, Forfeited/Expired	65.21
Weighted-Average Exercise Price, Outstanding, Ending balance	46.79	$ 44.45
Weighted-Average Exercise Price, Exercisable	36.50
Weighted-Average Exercise Price, Vested and expected to vest	$ 46.43
Weighted-Average Remaining Contractual Term (in years), Outstanding	7 years 3 months 11 days	7 years 5 months 27 days
Weighted-Average Remaining Contractual Term (in years), Exercisable	5 years 10 months 6 days
Weighted-Average Remaining Contractual Term (in years), Vested and expected to vest	7 years 2 months 23 days
Aggregate Intrinsic Value, Outstanding	$ 63,559	$ 153,573
Aggregate Intrinsic Value, Exercisable	53,952
Aggregate Intrinsic Value, Vested and expected to vest	$ 63,351

Share-Based Payments - Summar44

Share-Based Payments - Summary of Unvested RSUs Activity (Detail) - Restricted Stock Units (RSUs) [Member] - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested shares beginning of period	15,000
Granted	69,550	15,000	10,000
Vested	(7,500)
Unvested shares end of period	77,050	15,000
Weighted-average grant date fair value, Unvested shares beginning of period	$ 122.22
Weighted-average grant date fair value, Granted	41.77
Weighted-average grant date fair value, Vested	122.22
Weighted-average grant date fair value, Unvested shares end of period	$ 49.60	$ 122.22

Share-Based Payments - Schedule

Share-Based Payments - Schedule of Performance-Based Units (Detail) - Performance-Based Stock Units (PSUs) [Member]	12 Months Ended
	Dec. 31, 2016$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested shares beginning of period | shares	100,270
Granted | shares	114,503
Vested | shares	0
Forfeited/expired | shares	(14,160)
Unvested shares end of period | shares	200,613
Weighted-average grant date fair value, Unvested shares beginning of period | $ / shares	$ 64.44
Weighted-average grant date fair value, Granted | $ / shares	45.02
Weighted-average grant date fair value, Vested | $ / shares	0
Weighted-average grant date fair value, Forfeited/expired | $ / shares	64.44
Weighted-average grant date fair value, Unvested shares end of period | $ / shares	$ 53.36

Share-Based Payments - Stock-Ba

Share-Based Payments - Stock-Based Compensation Expense for Employee and Non-Employee Stock Options, Restricted Stock Units, Performance-Based Stock Options, Performance-Based Stock Units and Employee Stock Purchase Plan Shares (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation expense	$ 42,086	$ 31,963	$ 11,506
Research and development expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation expense	25,386	17,419	6,688
General and administrative expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation expense	$ 16,700	$ 14,544	$ 4,818

Share-Based Payments - Schedu47

Share-Based Payments - Schedule of Grant Date Fair Value Option Award Weighted Average Assumptions Used (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Risk-free interest rate	1.42%	1.71%	1.83%
Expected dividend yield	0.00%	0.00%	0.00%
Expected term (in years)	6 years 18 days	6 years 15 days	6 years 11 days
Expected volatility	72.84%	69.62%	78.61%

Income Taxes - Schedule of Dome

Income Taxes - Schedule of Domestic and Foreign Components of Loss Before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Domestic	$ (179,896)	$ (111,057)	$ (53,930)
Foreign	(18,575)	(6,674)
Loss before income taxes	$ (198,471)	$ (117,731)	$ (53,930)

Income Taxes - Provision (Benef

Income Taxes - Provision (Benefit) for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current:
Federal			$ (444)
State			18
Foreign	$ 0	$ 0	0
Total current			(426)
Deferred:
Federal	0	0	0
State	0	0	0
Foreign	0	0	0
Total deferred	$ 0	$ 0	0
Total			$ (426)

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Expected Income Tax Benefit (Expense) Computed Using Federal Statutory Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income tax benefit computed at federal statutory tax rate	35.00%	35.00%	35.00%
State taxes, net of federal benefit	2.90%	4.50%	4.90%
Change in valuation allowance	(43.40%)	(44.60%)	(35.80%)
General business credits and other credits	9.50%	8.40%	(1.90%)
Permanent differences	(0.20%)	(0.20%)	(0.10%)
Incentive Stock Options	(1.80%)	(1.80%)	(2.00%)
Foreign Rate Differential	(1.90%)	(1.20%)
Other	(0.10%)	(0.10%)	0.80%
Total	0.00%	0.00%	0.90%

Income Taxes - Company's Deferr

Income Taxes - Company's Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Net operating loss carryforwards	$ 126,077	$ 81,947
Deferred revenue	8,051	7,046
Tax credit carryforwards	43,350	16,708
Purchased intangible assets	4,410	724
Stock-based compensation	22,731	11,923
Deferred rent	8,516	7,975
Non-deductible accruals and reserves	3,310	2,520
Total deferred tax assets	216,445	128,843
Valuation allowance	(208,033)	(121,874)
Total deferred tax assets	8,412	6,969
Deferred tax liabilities:
Depreciation and amortization	(8,412)	(6,969)
Total deferred tax liabilities	(8,412)	(6,969)
Net deferred tax asset	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016USD ($)Audit	Dec. 31, 2015USD ($)Audit	Dec. 31, 2011Ownership	Mar. 31, 2017USD ($)
Income Taxes Disclosure [Line Items]
Expiration date of carryforwards	Dec. 31, 2036
Percentage of increase the ownership	5.00%
Aggregate period	3 years
Number of ownership change | Ownership			2
Amount of valuation allowance on deferred tax assets	$ 208,033,000	$ 121,874,000
Increase in valuation allowance	86,100,000
Unrecognized tax benefits	$ 0	$ 0
Number of federal, state or foreign audit in process | Audit	0	0
ASU 2016-09 [Member] | Scenario, Forecast [Member]
Income Taxes Disclosure [Line Items]
Increase in deferred tax assets				$ 32,700,000
Federal Orphan Drug Tax Credit [Member]
Income Taxes Disclosure [Line Items]
Research and development tax credit	$ 33,300,000
Minimum [Member]
Income Taxes Disclosure [Line Items]
Shareholders in the stock of a corporation	50.00%
Federal Income Tax [Member]
Income Taxes Disclosure [Line Items]
Net operating loss	$ 387,200,000
Federal Income Tax [Member] | Research Tax Credit Carryforward [Member]
Income Taxes Disclosure [Line Items]
Research and development tax credit	7,300,000
State Income Tax [Member]
Income Taxes Disclosure [Line Items]
Net operating loss	391,500,000
State Income Tax [Member] | Research Tax Credit Carryforward [Member]
Income Taxes Disclosure [Line Items]
Research and development tax credit	4,200,000
Foreign Income Tax [Member]
Income Taxes Disclosure [Line Items]
Net operating loss	20,200,000
State and Local Jurisdiction [Member]
Income Taxes Disclosure [Line Items]
Net operating loss	81,900,000
Federal [Member]
Income Taxes Disclosure [Line Items]
Net operating loss	$ 77,800,000

Defined Contribution Benefit 53

Defined Contribution Benefit Plan - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Employer's contributions		50.00%
Employer's contributions of eligible compensation		6.00%
Contribution by the company	$ 1,000,000	$ 700,000	$ 0

Selected Quarterly Financial 54

Selected Quarterly Financial Data (Unaudited) - Summary of Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Total revenue	$ 22,648	$ 8,985	$ 6,978	$ 31,281	$ 6,218	$ 5,480	$ 13,219	$ 34,202
Loss from operations	(57,409)	(63,512)	(56,470)	(23,594)	(40,897)	(40,475)	(32,133)	(5,195)	$ (200,985)	$ (118,700)	$ (54,133)
Net loss	$ (56,486)	$ (62,834)	$ (55,953)	$ (23,198)	$ (40,621)	$ (40,257)	$ (31,897)	$ (4,957)
Net loss per share - basic and diluted	$ (1.34)	$ (1.63)	$ (1.47)	$ (0.61)	$ (1.08)	$ (1.07)	$ (0.85)	$ (0.13)	$ (5.07)	$ (3.15)	$ (1.59)