Infinity Pharmaceuticals (INFIQ) 10-K 15 Mar 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Mar. 01, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	INFI
Entity Registrant Name	INFINITY PHARMACEUTICALS, INC.
Entity Central Index Key	1,113,148
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)		51,961,800
Entity Public Float			$ 78,050,216

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 34,607	$ 74,060
Available-for-sale securities	23,002	18,004
Restricted cash	0	1,152
Prepaid expenses and other current assets	777	8,444
Total current assets	58,386	101,660
Property and equipment, net (note 7)	219	23,424
Restricted cash, less current portion	0	530
Other assets	748	41
Total assets	59,353	125,655
Current liabilities:
Accounts payable	459	2,413
Accrued expenses	5,136	21,008
Note payable (note 11)	6,000	0
Financing obligation, current (note 7)	0	442
Total current liabilities	11,595	23,863
Deferred rent, less current portion (note 7)	0	183
Financing obligation, less current portion (note 7)	0	19,149
Other liabilities	28	6
Total liabilities	11,623	43,201
Commitments and contingencies (note 10)
Stockholders’ equity:
Preferred Stock, $0.001 par value; 1,000,000 shares authorized, no shares issued and outstanding at December 31, 2017 and 2016	0	0
Common Stock, $0.001 par value; 100,000,000 shares authorized, 50,761,039 and 50,374,871 shares issued and outstanding at December 31, 2017 and December 31, 2016, respectively	51	50
Additional paid-in capital	715,213	708,096
Accumulated deficit	(667,519)	(625,689)
Accumulated other comprehensive loss	(15)	(3)
Total stockholders’ equity	47,730	82,454
Total liabilities and stockholders’ equity	$ 59,353	$ 125,655

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	1,000,000	1,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common Stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common Stock, shares authorized (in shares)	100,000,000	100,000,000
Common Stock, shares issued (in shares)	50,761,039	50,374,871
Common Stock, shares outstanding (in shares)	50,761,039	50,374,871

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Collaboration revenue	$ 6,000	$ 18,723	$ 109,066
Operating expenses:
Research and development	20,830	119,611	199,109
General and administrative	21,615	42,219	37,065
Total operating expenses	42,445	161,830	236,174
Gain on AbbVie Opt-Out (note 11)	0	112,216	0
Income (loss) from operations	(36,445)	(30,891)	(127,108)
Other income (expense):
Interest expense	(1,010)	(1,225)	(1,368)
Other expense (note 7)	(6,882)	0	0
Investment and other income	1,787	2,015	435
Total other income (expense)	(6,105)	790	(933)
Loss before income taxes	(42,550)	(30,101)	(128,041)
Income taxes benefit (expense)	720	0	(335)
Net income (loss)	$ (41,830)	$ (30,101)	$ (128,376)
Basic and diluted loss per common share (in dollars per share)	$ (0.83)	$ (0.61)	$ (2.62)
Basic and diluted weighted average number of common shares outstanding (in shares)	50,560,195	49,608,234	49,083,479
Other comprehensive loss:
Net unrealized holding losses on available-for-sale securities arising during the period	$ (12)	$ (48)	$ (69)
Comprehensive loss	$ (41,842)	$ (30,149)	$ (128,445)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net loss	$ (41,830)	$ (30,101)	$ (128,376)
Adjustments to reconcile net loss to net cash used in operating activities:
Non-cash gain on AbbVie Opt-Out (note 11)	0	(112,216)	0
Note payable (note 11)	6,000	0	0
Depreciation	1,715	3,418	2,292
Stock-based compensation, including 401(k) match	6,972	13,714	14,700
Non-cash adjustment to financing obligation	1,882	0	0
Impairment of property and equipment	0	771	0
Gain on sale of fixed assets	(736)	(876)	0
Amortization of loan commitment asset	0	0	647
Net amortization of premium/discount on available-for-sale securities	(25)	159	272
Other, net	0	(2)	(162)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	7,110	5,208	933
Accounts payable, accrued expenses and other liabilities	(17,799)	(15,708)	11,774
Due to Takeda	0	0	(6,667)
Deferred revenue	0	(18,723)	20,934
Net cash used in operating activities	(36,711)	(154,356)	(83,653)
Investing activities
Purchases of property and equipment	(43)	(661)	(6,426)
Proceeds from sale of assets	750	2,140	0
Purchases of available-for-sale securities	(23,985)	(66,503)	(121,456)
Proceeds from maturities of available-for-sale securities	19,000	93,400	89,515
Proceeds from sales of available-for-sale securities	0	11,953	464
Net cash provided by (used in) investing activities	(4,278)	40,329	(37,903)
Financing activities
Proceeds from issuances of common stock, net	146	332	2,830
Payments on construction liability	0	0	(273)
Payments on financing obligation	(292)	(415)	(236)
Restricted cash	1,682	0	0
Net cash provided by (used in) financing activities	1,536	(83)	2,321
Net decrease in cash and cash equivalents	(39,453)	(114,110)	(119,235)
Cash and cash equivalents at beginning of period	74,060	188,170	307,405
Cash and cash equivalents at end of period	34,607	74,060	188,170
Supplemental cash flow information
Cash paid for interest	802	1,225	721
Cash paid for income taxes	0	5	885
Supplemental schedule of noncash investing and financing activities
Reclassification to financing obligation	0	0	19,273
Property and equipment in accrued expenses	0	0	65
Increase in property and equipment for amount paid by landlord	$ 0	$ 0	$ 5,059

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Beginning Balance (in shares) at Dec. 31, 2014		48,878,828
Beginning Balance at Dec. 31, 2014	$ 209,472	$ 49	$ 676,521	$ (467,212)	$ 114
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)		225,578
Exercise of stock options	1,796		1,796
Stock-based compensation expense	13,844		13,844
401(k) plan match issued in common stock (in shares)		68,235
401(k) plan match issued in common stock	856		856
Issuance of common stock related to employee stock purchase plan (in shares)		124,358
Issuance of common stock related to employee stock purchase plan	964		964
Issuance of common stock (in shares)		8,137
Issuance of common stock	70		70
Unrealized loss on marketable securities	(69)				(69)
Net loss	(128,376)			(128,376)
Ending Balance (in shares) at Dec. 31, 2015		49,305,136
Ending Balance at Dec. 31, 2015	98,557	$ 49	694,051	(595,588)	45
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)		67,077
Exercise of stock options	373		373
Stock-based compensation expense	11,937		11,937
401(k) plan match issued in common stock (in shares)		295,596
401(k) plan match issued in common stock	619		619
Issuance of common stock related to employee stock purchase plan (in shares)		15,860
Issuance of common stock related to employee stock purchase plan	18		18
Vesting of restricted stock and other, net (in shares)		691,202
Vesting of restricted stock and other, net	1,099	$ 1	1,098
Unrealized loss on marketable securities	(48)				(48)
Net loss	(30,101)			(30,101)
Ending Balance (in shares) at Dec. 31, 2016		50,374,871
Ending Balance at Dec. 31, 2016	$ 82,454	$ 50	708,096	(625,689)	(3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)	0
Stock-based compensation expense	$ 6,526		6,526
401(k) plan match issued in common stock (in shares)		111,235
401(k) plan match issued in common stock	136		136
Issuance of common stock related to employee stock purchase plan (in shares)		38,648
Issuance of common stock related to employee stock purchase plan	56		56
Vesting of restricted stock and other, net (in shares)		236,285
Vesting of restricted stock and other, net	400	$ 1	399
Unrealized loss on marketable securities	(12)				(12)
Net loss	(41,830)			(41,830)
Ending Balance (in shares) at Dec. 31, 2017		50,761,039
Ending Balance at Dec. 31, 2017	$ 47,730	$ 51	$ 715,213	$ (667,519)	$ (15)

Organization

Organization	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	1. Organization Infinity Pharmaceuticals, Inc., is an innovative biopharmaceutical company dedicated to developing novel medicines for people with cancer. As used throughout these audited, consolidated financial statements, the terms “Infinity,” “we,” “us,” and “our” refer to the business of Infinity Pharmaceuticals, Inc., and its wholly-owned subsidiaries.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation These consolidated financial statements include the accounts of Infinity and its wholly-owned subsidiaries. We have eliminated all significant intercompany accounts and transactions in consolidation. The preparation of consolidated financial statements in accordance with generally accepted accounting principles requires our management to make estimates and judgments that may affect the reported amounts of assets, liabilities, revenues and expenses, and related disclosure of contingent assets and liabilities. On an ongoing basis, we evaluate our estimates and judgments. We base our estimates on historical experience and on various other assumptions that are believed to be reasonable, the results of which form the basis for making judgments about the carrying values of assets and liabilities. Actual results may differ from these estimates under different assumptions or conditions. Cash Equivalents and Available-For-Sale Securities Cash equivalents and available-for-sale securities primarily consist of money market funds and U.S. government-sponsored enterprise obligations. We consider all highly liquid investments with maturities of three months or less at the time of purchase to be cash equivalents. Cash equivalents, which consist of money market funds, corporate obligations and U.S. government-sponsored enterprise obligations, are stated at fair value. They are also readily convertible to known amounts of cash and have such short-term maturities that each presents insignificant risk of change in value due to changes in interest rates. Our classification of cash equivalents is consistent with prior periods. We determine the appropriate classification of marketable securities at the time of purchase and reevaluate such designation at each balance sheet date. We have classified all of our marketable securities at December 31, 2017 and 2016 as “available-for-sale.” We carry available-for-sale securities at fair value, with the unrealized gains and losses reported in accumulated other comprehensive income (loss), which is a separate component of stockholders’ equity. We adjust the cost of available-for-sale debt securities for amortization of premiums and accretion of discounts to maturity. We include such amortization and accretion in investment and other income. The cost of securities sold is based on the specific identification method. We include in investment income interest and dividends on securities classified as available-for-sale. We conduct periodic reviews to identify and evaluate each investment that is in an unrealized loss position in order to determine whether an other-than-temporary impairment exists. An unrealized loss exists when the current fair value of an individual security is less than its amortized cost basis. Unrealized losses on available-for-sale debt securities that are determined to be temporary, and not related to credit loss, are recorded, net of tax, in accumulated other comprehensive income (loss). For available-for-sale debt securities in an unrealized loss position, we perform an analysis to assess whether we intend to sell or whether we would more likely than not be required to sell the security before the expected recovery of the amortized cost basis. Where we intend to sell a security, or may be required to do so, the security’s decline in fair value is deemed to be other-than-temporary, and the full amount of the unrealized loss is recorded within earnings as an impairment loss. Regardless of our intent to sell a security, we perform additional analysis on all securities in an unrealized loss position to evaluate losses associated with the creditworthiness of the security. Credit losses are identified where we do not expect to receive cash flows sufficient to recover the amortized cost basis of a security and are recorded within earnings as an impairment loss. Liquidity As of December 31, 2017 , our cash, cash equivalents and available-for-sale securities balance was $57.6 million . Subsequent to December 31, 2017 , we prepaid the Takeda Note and accrued interest (see Note 11 ) with $4.0 million of cash and $2.3 million of stock and we raised $2.0 million with our at-the-market facility (see Note 17 ). We have primarily incurred operating losses since inception and have relied on our ability to fund our operations through collaboration and license arrangements and through the sale of stock. We expect to continue to spend significant resources to fund the development and potential commercialization of IPI-549 and to incur significant operating losses for the foreseeable future. In the absence of additional funding or business development activities, we believe that our existing cash, cash equivalents and available-for-sale securities will be adequate to satisfy our forecasted operating needs into the third quarter of 2019. We have no t included the future potential $22.0 million of Verastem Inc., or Verastem, milestone payment in this forecast (see Note 11 ). For more information, refer to the section titled “Liquidity and Capital Resources” in Item 7, Management’s Discussion and Analysis of Financial Condition and Results of Operations. Concentration of Risk Cash and cash equivalents are primarily maintained with two major financial institutions in the United States. Deposits at banks may exceed the insurance provided on such deposits. Generally, these deposits may be redeemed upon demand and, therefore, bear minimal risk. Financial instruments that potentially subject us to concentration of credit risk primarily consist of available-for-sale securities. Available-for-sale securities consist of U.S. Treasury securities and U.S. government-sponsored enterprise obligations. Our investment policy, which has been approved by our Board of Directors, limits the amount that we may invest in any one issuer of investments, thereby reducing credit risk concentrations. Segment Information We operate in one business segment, which focuses on drug development. We make operating decisions based upon performance of the enterprise as a whole and utilize our consolidated financial statements for decision making. All of our revenues to date have been generated under research collaboration agreements. Revenue associated with the contingent payment from Verastem accounted for all of our revenue during the year ended December 31, 2017 (see Note 11 ). Revenue related to the amortization of the deferred revenue associated with the grant of licenses to, and research and development services provided to, AbbVie Inc., or AbbVie, accounted for all of our revenue during the years ended December 31, 2015 and 2016 . Property and Equipment Property and equipment are stated at cost. Depreciation is recorded using the straight-line method over the estimated useful lives of the applicable assets. Application development costs incurred for computer software developed or obtained for internal use are capitalized. Upon sale or retirement, the cost and related accumulated depreciation are eliminated from the respective account, and the resulting gain or loss, if any, is included in current operations. Amortization of leasehold improvements, building improvements and capital leases is recorded as depreciation expense and included in research and development and general and administrative expense, as applicable. Repairs and maintenance charges that do not increase the useful life of the assets are charged to operations as incurred. Property and equipment are depreciated over the following periods: Computer equipment and software 3 to 5 years Leasehold improvements Shorter of lease term or useful life of asset Building and building improvements 10 to 50 years, less estimated residual Furniture and fixtures 7 to 10 years Impairment of Long-Lived Assets We evaluate our long-lived assets for potential impairment. Potential impairment is assessed when there is evidence that events or changes in circumstances have occurred that indicate that the carrying amount of a long-lived asset may not be recovered. Recoverability of these assets is assessed based on undiscounted expected future cash flows from the assets, considering a number of factors, including past operating results, budgets and economic projections, market trends and product development cycles. An impairment in the carrying value of each asset is assessed when the undiscounted expected future cash flows, including its eventual residual value, derived from the asset are less than its carrying value. Impairments, if any, are recognized in earnings. An impairment loss would be recognized in an amount equal to the excess of the carrying amount over the undiscounted expected future cash flows. Fair Value Measurements We define fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. We determine fair value based on the assumptions market participants use when pricing the asset or liability. We also use the fair value hierarchy that prioritizes the information used to develop these assumptions. We value our available-for-sale securities utilizing third-party pricing services. The pricing services use many observable market inputs to determine value, including benchmark yields, reportable trades, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, reference data, new issue data, monthly payment information and collateral performance. We validate the prices provided by our third-party pricing services by understanding the models used, obtaining market values from other pricing sources and confirming that those securities trade in active markets. Revenue Recognition To date, all of our revenue has been generated under research collaboration agreements. The terms of these research collaboration agreements may include payment to us of non-refundable, upfront license fees, funding or reimbursement of research and development efforts, milestone payments if specified objectives are achieved, and/or royalties on product sales. We evaluate all deliverables within an arrangement to determine whether or not they provide value on a stand-alone basis. Based on this evaluation, the deliverables are separated into units of accounting. For each unit of accounting identified within an arrangement, we determine the period over which the performance obligation occurs. Revenue is then recognized using the proportional performance method. The proportional performance method is used when the level of effort to complete the performance obligations under an arrangement can be reasonably estimated. We recognize revenue based upon our best estimate of the selling price for each element when there is no other means to determine the fair value of that item and allocate the consideration based on the relative values. The process for determining the best estimate of the selling price involves significant judgment and estimates. At the inception of each agreement that includes milestone payments, we evaluate whether each milestone is substantive on the basis of the contingent nature of the milestone. This evaluation includes an assessment of whether: • the consideration is commensurate with either (1) our performance to achieve the milestone, or (2) the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from our performance to achieve the milestone, • the consideration relates solely to past performance, and • the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. In making this assessment, we evaluate factors such as the clinical, regulatory, commercial and other risks that must be overcome to achieve the respective milestone, the level of effort and investment required, and whether the milestone consideration is reasonable relative to all deliverables and payment terms in the arrangement. We recognize revenues related to substantive milestones in full in the period in which the substantive milestone is achieved. If a milestone payment is not considered substantive, we recognize the amount associated with the applicable milestone based on the period over which the performance obligation occurs for each deliverable in the arrangement. We will recognize royalty revenue, if any, based upon actual and estimated net sales by the licensee of licensed products in licensed territories in the period the sales occur. We have not recognized any royalty revenue to date. Income Taxes We use the liability method to account for income taxes. Deferred tax assets and liabilities are determined based on differences between financial reporting and income tax basis of assets and liabilities, as well as net operating loss and tax credit carryforwards, and are measured using the enacted tax rates and laws that will be in effect when the differences reverse. Deferred tax assets are reduced by a valuation allowance to reflect the uncertainty associated with their ultimate realization. The effect of a change in tax rate on deferred taxes is recognized in income or loss in the period that includes the enactment date. We use our judgment for the financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. We recognize any material interest and penalties related to unrecognized tax benefits in income tax expense. Due to the uncertainty surrounding the realization of the net deferred tax assets in future periods, we have recorded a full valuation allowance against our otherwise recognizable net deferred tax assets as of December 31, 2017 and 2016 . Basic and Diluted Net Loss per Common Share Basic net loss per share is based upon the weighted average number of common shares outstanding during the period, excluding restricted stock that has been issued but has not yet vested. Diluted net loss per share is based upon the weighted average number of common shares outstanding during the period plus the effect of additional weighted average common equivalent shares outstanding during the period when the effect of adding such shares is dilutive. Common equivalent shares result from the assumed exercise of outstanding stock options and the exercise of outstanding warrants (the proceeds of which are then assumed to have been used to repurchase outstanding stock using the treasury stock method) and the vesting of restricted shares of common stock. In addition, the assumed proceeds under the treasury stock method include the average unrecognized compensation expense of stock options that are in-the-money. This results in the “assumed” buyback of additional shares, thereby reducing the dilutive impact of stock options. The two-class method is used for outstanding warrants as such warrants are considered to be participating securities, and such method is more dilutive than the treasury stock method. The following outstanding shares of common stock equivalents were excluded from the computation of net loss per share attributable to common stockholders for the periods presented because including them would have been antidilutive: At December 31, 2017 2016 2015 Stock options 7,460,722 6,067,945 8,265,577 Warrants 1,000,000 1,000,000 1,000,000 Unvested restricted stock — 797,111 — Comprehensive Loss Comprehensive loss is comprised of net loss and other comprehensive income (loss). Other comprehensive income (loss) is comprised of unrealized holding gains and losses arising during the period on available-for-sale securities that are not other-than-temporarily impaired. During the year ended December 31, 2017 , there were no material reclassifications out of accumulated other comprehensive income (loss). Stock-Based Compensation Expense For awards granted to employees and directors, including our 2013 Employee Stock Purchase Plan, or ESPP, we measure stock-based compensation cost at the grant date based on the estimated fair value of the award and recognize it as expense over the requisite service period on a straight-line basis. We record the expense of services rendered by non-employees based on the estimated fair value of the stock option as of the respective vesting date. We use the Black-Scholes valuation model in determining the fair value of all equity awards. For awards with performance conditions, we estimate the likelihood of satisfaction of the performance conditions, which affects the period over which the expense is recognized. When the performance conditions related to these awards are determined to be probable, we recognize the expense over the requisite service period. We have no awards with market conditions. Research and Development Expense Research and development expense consists of expenses incurred in performing research and development activities, including salaries and benefits, overhead expenses including facilities expenses, materials and supplies, preclinical expenses, clinical trial and related clinical manufacturing expenses, comparator and combination drug expenses, stock-based compensation expense, depreciation of equipment, contract services, and other outside expenses. We also include as research and development expense upfront license payments related to acquired technologies which have not yet reached technological feasibility and have no alternative use. We expense research and development costs as they are incurred. Prepaid comparator and combination drug expenses are capitalized and then recognized as expense when title transfers to us. We have been a party to collaboration agreements in which we were reimbursed for work performed on behalf of the collaborator, as well as one in which we reimbursed the collaborator for work it had performed. We record all appropriate expenses under our collaborations as research and development expense. If the arrangement provides for reimbursement of research and development expenses incurred by us, we evaluate the terms of the arrangement to determine whether the reimbursement should be recorded as revenue or as an offset to research and development expense. If the arrangement provides for us to reimburse the collaborator for research and development expenses or for the achievement of a development milestone for which a payment is due, we record the reimbursement or the achievement of the development milestone as research and development expense. Reclassifications Certain amounts in the prior years’ financial statements have been reclassified to conform with the current year presentation. Adjustments have been made to the Consolidated Statements of Cash Flows and the prepaid expenses and other current assets and accrued expenses footnotes to aggregate certain items. These reclassifications have no impact on previously reported net income, net loss or cash flows. New Accounting Pronouncements In May 2014, the Financial Accounting Standards Board, or FASB, issued Accounting Standard Update, or ASU, No. 2014-9, Revenue from Contracts with Customers , or ASU No. 2014-9, which supersedes all existing revenue recognition requirements, including most industry-specific guidance. The new standard requires a company to recognize revenue when it transfers goods or services to customers in an amount that reflects the consideration that the company expects to receive for those goods or services. ASU No. 2014-9 was originally effective for interim and annual periods beginning after December 15, 2016. In August 2015, the FASB issued a one-year deferral of the effective date of this standard to annual reporting periods, and interim reporting periods within those years, beginning after December 15, 2017. Entities are allowed to adopt the standard as of the original effective date. The standard allows for two transition methods - full retrospective, in which the standard is applied to each prior reporting period presented or modified retrospective, in which the cumulative effect of initially applying the standard recognized at the date of initial adoption. We elected the modified retrospective approach and adopted the new standard effective January 1, 2018. We have substantially completed our assessment of the standard on our two out-licensing arrangements and do not expect the adoption of the standard to have a material impact on our financial position and results of operations when applied to our out-licensing arrangements. We will complete our assessment in the first quarter of 2018. In February 2016, the FASB issued ASU No. 2016-02, Leases, or ASU No. 2016-02 , which requires lessees to recognize the assets and liabilities arising from leases on the balance sheet. ASU No. 2016-02 is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Early adoption is permitted. We are currently evaluating the method of adoption and the potential impact that ASU No. 2016-02 may have on our financial position and results of operations. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments, or ASU No. 2016-15. The new standard clarifies classification of certain cash receipts and cash payments on the statement of cash flows to reduce existing diversity in practice. The new accounting guidance will be effective on January 1, 2018. The adoption of ASU No. 2016-15 will not have an impact on our consolidated financial statements. In November 2016, FASB issued ASU No. 2016-18, Statement of Cash Flows, Restricted Cash, or ASU No. 2016-18. ASU No. 2016-18 provides guidance on the presentation of restricted cash and restricted cash equivalents in the statement of cash flows. Under ASU No. 2016-18, the statement of cash flows shall explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Amounts generally described as restricted cash and cash equivalents should now be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period amounts shown on the statements of cash flows. The amendments of this ASU are effective for reporting periods beginning after December 15, 2017, with early adoption permitted. Other than the revised statement of cash flows presentation, the adoption of ASU No. 2016-18 will not have an impact on our consolidated financial statements. In May 2017, FASB issued ASU No. 2017-09, Compensation—Stock Compensation: Scope of Modification Accounting, or ASU No. 2017-09. ASU No. 2017-09 clarifies when changes to the terms and conditions of a share-based payment award must be accounted for as modifications. The new guidance will reduce diversity in practice and result in fewer changes to the terms of an award being accounted for as modifications. It does not change the accounting for modifications. ASU No. 2017-09 is effective for reporting periods beginning after December 15, 2017, with early adoption permitted. The adoption of ASU No. 2017-09 will not have an impact on our consolidated financial statements. Recently Adopted Accounting Pronouncements In March 2016, the FASB issued ASU No. 2016-09, Improvements to Employee Share-Based Payment Accounting , or ASU No. 2016-09, which simplifies several aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities and classification of cash flows. We adopted ASU No. 2016-09 as of January 1, 2017. Under the new standard, all excess tax benefits and tax deficiencies are recognized as income tax expense or benefit in the statement of operations. The tax effects of exercised or vested awards are treated as discrete items in the reporting period in which they occur. We applied the modified retrospective adoption approach upon adoption of the standard, and prior periods have not been adjusted. As a result, we established a net operating loss deferred tax asset of $7.5 million to account for prior period excess tax benefits through retained earnings and an offsetting valuation allowance of $7.5 million through retained earnings because it is not more likely than not that the deferred tax asset will be realized due to historical and expected future losses. We elected to recognize forfeitures related to employee share-based payments as they occur. There was not a material impact on our financial statements as a result of the adoption of this guidance.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	3. Stock-Based Compensation Under each of the stock incentive plans described below, stock option awards made to new employees upon commencement of employment typically provide for vesting of 25% of the shares underlying the award at the end of the first year of service with the remaining 75% of the shares underlying the award vesting ratably on a monthly basis over the following three -year period subject to continued service. Annual grants to existing employees typically provide for ratable vesting over specified periods determined by the Board of Directors. In addition, under each plan, all options granted expire no later than ten years after the date of grant. 2010 Stock Incentive Plan Our 2010 Stock Incentive Plan, or the 2010 Plan, was approved by our stockholders in May 2010. The 2010 Plan provides for the grant of incentive stock options intended to qualify under Section 422 of the Internal Revenue Code of 1986, as amended, or IRC, as well as nonstatutory stock options, stock appreciation rights, restricted stock, restricted stock units and other stock-based and cash-based awards. Up to 9,785,000 shares of our common stock may be issued pursuant to awards granted under the 2010 Plan, plus an additional amount of our common stock underlying awards issued under the 2000 Stock Incentive Plan, or the 2000 Plan, that expire or are canceled without the holders receiving any shares under those awards. As of December 31, 2017 , an aggregate of 6,797,090 shares of our common stock were reserved for issuance upon the exercise of outstanding awards, and up to 2,619,290 shares of common stock may be issued pursuant to awards granted under the 2010 Plan. 2000 Stock Incentive Plan The 2000 Stock Incentive Plan, or the 2000 Plan, provided for the grant of stock options intended to qualify as incentive stock options under the IRC, as well as nonstatutory stock options and restricted stock. As of December 31, 2017 , an aggregate of 663,632 shares of our common stock were reserved for issuance upon the exercise of outstanding awards granted under the 2000 Plan. The 2000 Plan was terminated upon approval of the 2010 Plan; therefore, no further grants may be made under the 2000 Plan. 2013 Employee Stock Purchase Plan Our ESPP permits eligible employees to purchase shares of our common stock at a discount and consists of consecutive, overlapping 24 -month offering periods, each consisting of four six -month purchase periods. On the first day of each offering period, each employee who is enrolled in the ESPP will automatically receive an option to purchase up to a whole number of shares of our common stock. The purchase price of each of the shares purchased in a given purchase period will be 85% of the closing price of a share of our common stock on the first day of the offering period or the last day of the purchase period, whichever is lower. We temporarily suspended the ESPP program on June 24, 2016, and our Board of Directors approved the commencement of a new offering period in June 2017. During 2017 , 38,648 shares of common stock were purchased for total proceeds of approximately $0.1 million . During 2016 , 15,860 shares of common stock were purchased for total proceeds of approximately $18,000 . During 2015 , 124,358 shares of common stock were purchased for total proceeds of approximately $1.0 million . Compensation Expense Total stock-based compensation expense, related to all equity awards, comprised the following: Year Ended December 31, 2017 2016 2015 (in thousands) Research and development $ 1,756 $ 6,421 $ 8,474 General and administrative 5,216 7,293 6,226 Total stock-based compensation expense $ 6,972 $ 13,714 $ 14,700 As of December 31, 2017 , we had approximately $3.3 million of total unrecognized compensation cost related to unvested common stock options and awards under our ESPP, which are expected to be recognized over a weighted-average period of 1.3 years . Restricted Stock During 2016, our Board of Directors approved grants of 1,792,250 shares of restricted common stock to eligible employees who continue employment with us. The restricted stock was granted pursuant to our 2010 Plan, is subject to forfeiture and will vest based on the achievement of specified performance conditions. The grant date fair value of the restricted stock is based on the closing price of our common stock on each of the grant dates. We recognized $0.3 million and $1.2 million of stock compensation expense based on the fair value measured on the date of grant for the years ended December 31, 2017 and 2016 related to the vested restricted stock. The total fair value measured on the vesting date of the restricted stock that vested during the years ended December 31, 2017 and 2016 was $0.3 million and $0.9 million , respectively. A summary of our restricted stock activity for the year ended December 31, 2017 is as follows: Restricted Stock Weighted-Average Grant-Date Fair Value Unvested at January 1, 2017 797,111 $ 1.43 Granted — — Vested (190,989 ) 1.54 Canceled (606,122 ) 1.40 Unvested at December 31, 2017 — $ — Stock Options Valuation Assumptions We estimate the fair value of stock options at the date of grant using the Black-Scholes valuation model with the following weighted-average assumptions: December 31, 2017 2016 2015 Risk-free interest rate 1.9 % 1.8 % 1.5 % Expected annual dividend yield — — — Expected stock price volatility 90.1 % 73.0 % 70.8 % Expected term of options 5.6 years 5.4 years 5.4 years The valuation assumptions were determined as follows: • Risk-free interest rate: The yield on zero-coupon U.S. Treasury securities for a period that was commensurate with the expected term of the awards. • Expected annual dividend yield: The estimate for annual dividends was zero because we have not historically paid a dividend and do not intend to do so in the foreseeable future. • Expected stock price volatility: We determined the expected volatility by using our available implied and historical price information. • Expected term of options: The expected term of the awards represents the period of time that the awards were expected to be outstanding. In prior years, we used historical data and expectations for the future to estimate employee exercise and post-vest termination behavior. For 2017, we used the simplified method to estimate expected term, whereby, the expected life equals the average of the vesting term and the original contractual term of the option. Following the adoption of ASU No. 2016-09, we recognize forfeitures related to employee share-based payments as they occur. All options granted to employees during the years ended December 31, 2017 , 2016 and 2015 were granted with exercise prices equal to the fair market value of our common stock on the date of grant. We consider the closing price of our common stock as reported on the Nasdaq Global Select Market to be the fair market value. A summary of our stock option activity for the year ended December 31, 2017 is as follows: Stock Options Weighted- Average Exercise Price Weighted-Average Remaining Contractual Life (years) Aggregate Intrinsic Value (in millions) Outstanding at January 1, 2017 6,067,945 $ 12.06 Granted 4,796,500 1.61 Exercised — — Forfeited (3,403,723 ) 10.57 Outstanding at December 31, 2017 7,460,722 $ 6.02 7.2 $ 2.0 Exercisable at December 31, 2017 3,028,913 $ 11.53 4.8 $ 0.2 The weighted-average fair value per share of options granted during the years ended December 31, 2017 , 2016 and 2015 was $1.17 , $3.75 and $8.48 , respectively. The aggregate intrinsic value of options outstanding at December 31, 2017 was calculated based on the positive difference between the closing fair market value of our common stock on December 31, 2017 and the exercise price of the underlying options. During the year ended December 31, 2017 , there were no options exercised. The aggregate intrinsic value of options exercised during the years ended December 31, 2016 and 2015 was approximately $0.1 million and $1.5 million , respectively. No related income tax benefits were recorded during the years ended December 31, 2017 , 2016 or 2015 . We settle employee stock option exercises with newly issued shares of our common stock. Employee Stock Purchase Plan The weighted-average fair value of each purchase right granted during the year ended December 31, 2017 , 2016 and 2015 was $0.99 , $2.91 and $4.24 , respectively. For the years ended December 31, 2017 , 2016 and 2015 , the fair values were estimated using the Black-Scholes valuation model using the following weighted-average assumptions: Year Ended December 31, 2017 2016 2015 Risk-free interest rate 1.2 % 0.8 % 0.4 % Expected annual dividend yield — — — Expected stock price volatility 102.3 % 63.5 % 60.3 % Expected term of options 1.25 years 1.25 years 1.25 years

Cash, Cash Equivalents and Avai

Cash, Cash Equivalents and Available-for-Sale Securities	12 Months Ended
	Dec. 31, 2017
Cash and Cash Equivalents [Abstract]
Cash, Cash Equivalents and Available-for-Sale Securities	4. Cash, Cash Equivalents and Available-for-Sale Securities The following is a summary of cash, cash equivalents and available-for-sale securities: December 31, 2017 Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value (in thousands) Cash and cash equivalents $ 34,607 $ — $ — $ 34,607 Available-for-sale securities: U.S. Treasury securities due in one year or less 3,497 — (3 ) 3,494 U.S. government-sponsored enterprise obligations due in one year or less 19,520 — (12 ) 19,508 Total available-for-sale securities 23,017 — (15 ) 23,002 Total cash, cash equivalents and available-for-sale securities $ 57,624 $ — $ (15 ) $ 57,609 December 31, 2016 Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value (in thousands) Cash and cash equivalents $ 74,060 $ — $ — $ 74,060 Available-for-sale securities: U.S. Treasury securities due in one year or less 6,753 — (1 ) 6,752 U.S. government-sponsored enterprise obligations due in one year or less 11,254 — (2 ) 11,252 Total available-for-sale securities 18,007 — (3 ) 18,004 Total cash, cash equivalents and available-for-sale securities $ 92,067 $ — $ (3 ) $ 92,064 We held 13 debt securities at December 31, 2017 that had been in an unrealized loss position for less than twelve months. The fair value of these securities was $23.0 million . As of December 31, 2017 , we held no securities in foreign financial institutions. We evaluated our securities for other-than-temporary impairments based on quantitative and qualitative factors. We considered the decline in market value for these 13 securities to be primarily attributable to current economic and market conditions. It is not more likely than not that we will be required to sell these securities, and we do not intend to sell these securities before the recovery of their amortized cost bases. Based on our analysis, we do not consider these investments to be other-than-temporarily impaired as of December 31, 2017 . We had no material realized gains or losses on our available-for-sale securities for the years ended December 31, 2017 , 2016 and 2015 . There were no other-than-temporary impairments recognized for the years ended December 31, 2017 , 2016 and 2015 .

Fair Value

Fair Value	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value	5. Fair Value We use a valuation hierarchy for disclosure of the inputs used to measure fair value. This hierarchy prioritizes the inputs into three broad levels. Level 1 inputs, which we consider the highest level inputs, are quoted prices (unadjusted) in active markets for identical assets or liabilities. Level 2 inputs are quoted prices for similar assets and liabilities in active markets or inputs that are observable for the asset or liability, either directly or indirectly through market corroboration, for substantially the full term of the financial instrument. Level 3 inputs are unobservable inputs based on our own assumptions used to measure assets and liabilities at fair value. The classification of a financial asset or liability within the hierarchy is determined based on the lowest level input that is significant to the fair value measurement. For our fixed income securities, we reference pricing data supplied by our custodial agent and nationally known pricing vendors, using a variety of daily data sources, largely readily-available market data and broker quotes. We validate the prices provided by our third-party pricing services by reviewing their pricing methods and obtaining market values from other pricing sources. After completing our validation procedures, we did not adjust or override any fair value measurements provided by our pricing services as of December 31, 2017 and 2016 . The following table provides the assets carried at fair value measured on a recurring basis as of December 31, 2017 and 2016 : Level 1 Level 2 (in thousands) December 31, 2017 Assets: Cash and cash equivalents $ 34,607 $ — U.S. Treasury securities — 3,494 U.S. government-sponsored enterprise obligations — 19,508 Total $ 34,607 $ 23,002 December 31, 2016 Assets: Cash and cash equivalents $ 61,008 $ 13,052 U.S. Treasury securities — 6,752 U.S. government-sponsored enterprise obligations — 11,252 Total $ 61,008 $ 31,056 The fair value of the available-for-sale securities and cash and cash equivalents (including asset types listed below with maturities of three months or less at the time of purchase) is based on the following inputs for both U.S. Treasury securities and U.S, government-sponsored enterprise obligations: benchmark yields, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers and reference data including TRACE ® reported trades. The carrying amounts reflected in the consolidated balance sheets for prepaid expenses and other current assets, other assets, accounts payable and accrued expenses approximate their fair value due to their short-term maturities. There have been no changes to our valuation methods during the year ended December 31, 2017 . We evaluate transfers between levels at the end of each reporting period. There were no transfers of assets or liabilities between Level 1 and Level 2 during the year ended December 31, 2017 . We had no available-for-sale securities that were classified as Level 3 at any point during the year ended December 31, 2017 .

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	12 Months Ended
	Dec. 31, 2017
Prepaid Expense and Other Assets, Current [Abstract]
Prepaid Expenses and Other Current Assets	6. Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consist of the following: December 31, 2017 2016 (in thousands) Prepaid expenses $ 563 $ 3,336 Other current assets 214 5,108 Total prepaid expenses and other current assets $ 777 $ 8,444

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property and Equipment	7. Property and Equipment Property and equipment consist of the following: December 31, 2017 2016 (in thousands) Computer equipment and software $ 1,814 $ 4,411 Furniture and fixtures — 918 Building and building improvements — 23,586 Leasehold improvements 16 431 1,830 29,346 Less accumulated depreciation (1,611 ) (5,922 ) $ 219 $ 23,424 On September 25, 2014, we entered into a lease agreement, or the Lease, with BHX, LLC, as trustee of 784 Realty Trust, or the Landlord, for the lease of office space at 784 Memorial Drive, Cambridge, Massachusetts. The term of the Lease commenced on November 1, 2014 , the Commencement Date, and was to expire on March 31, 2025 . Pursuant to the Lease, on the Commencement Date we agreed to lease the entire building consisting of approximately 61,000 square feet. On the Commencement Date, building construction was initiated to suit our then-anticipated future needs. We were responsible for the construction project, including having responsibility to pay for a portion of the structural elements of the building and bearing the risk of cost overruns. As such, we were deemed the owner of the building for accounting purposes, and we recorded the building in our property and equipment balance, although legal ownership remained with the Landlord. Our balance sheet also reflected a financing obligation related to this building. Depreciation on the building and building improvements commenced in June 2015. At December 31, 2016, the accompanying consolidated balance sheet reflects the building and building improvements, net of accumulated depreciation, of approximately $22.0 million and a financing obligation of approximately $19.6 million . On March 27, 2017, we and the Landlord entered into an amendment to the Lease under which we and the Landlord agreed to the early termination of the Lease subject to the satisfaction of specified contingencies, which we refer to as Lease Termination Contingencies, and a termination payment of $5.0 million , which we refer to as the Termination Payment and describe further below. The Lease amendment was extended by entry into a second lease amendment dated May 1, 2017 and a third lease amendment dated May 31, 2017. We refer to the Lease amendment and its extensions as the Lease Amendments. The Lease Termination Contingencies were satisfied on June 15, 2017 and, pursuant to the Lease Amendments, we paid the first installment of the Termination Payment to the Landlord on June 19, 2017 of $4.5 million and the final installment of the Termination Payment on August 24, 2017 of $0.5 million . The Lease, as amended, terminated effective August 31, 2017. Upon lease termination, the net carrying value of the building and building improvements, leasehold improvements, and the related financing obligation and deferred rent at August 31, 2017 were removed from our consolidated balance sheet. During the year ended December 31, 2017 , we recorded other expense of $6.9 million which represents the loss incurred to terminate the financing obligation in connection with the August 31, 2017 lease termination. This loss was comprised of: (i) $1.9 million representing the difference between the carrying value of the building and building improvements and the related financing obligation and deferred rent at August 31, 2017; and (ii) the $5.0 million Termination Payment. We provided a security deposit to the Landlord in the form of a letter of credit in the initial amount of $1.0 million , which was reduced by $0.5 million in April 2017. The remaining $0.5 million was returned to us in September 2017 following the payment of the final installment of the Termination Payment. During the year ended December 31, 2017 , we retired or sold certain personal property, computer equipment and furniture and fixtures that had a net book value of approximately $0.2 million for proceeds of $0.9 million resulting in a net gain of $0.7 million . During the year ended December 31, 2016 , we retired or sold certain laboratory equipment, computer equipment, furniture and fixtures and leasehold improvements that had a net book value of approximately $1.3 million for proceeds of $2.1 million , resulting in a net gain of $0.9 million . During the year ended December 31, 2016 , we identified and recorded the impairment of approximately $0.8 million of our property and equipment related to the strategic restructuring of our company. See Note 12 for additional information on the impairment.

Restricted Cash

Restricted Cash	12 Months Ended
	Dec. 31, 2017
Cash and Cash Equivalents [Abstract]
Restricted Cash	8. Restricted Cash We held $1.7 million in restricted cash as of December 31, 2016 . The balances were held on deposit with a bank to collateralize standby letters of credit in the name of our facility lessors in accordance with our facility lease agreements. During the year ended December 31, 2017, the $1.7 million was returned to us following the termination of our lease agreements (see Note 7 and Note 10 related to the lease terminations).

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
Accrued Expenses	9. Accrued Expenses Accrued expenses consisted of the following: December 31, 2017 2016 (in thousands) Accrued restructuring $ — $ 6,920 Accrued compensation and benefits 2,002 5,445 Accrued clinical and development 1,736 7,367 Other 1,398 1,276 Total accrued expenses $ 5,136 $ 21,008

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	10. Commitments and Contingencies We currently sublease 6,091 square feet of office space at 784 Memorial Drive, Cambridge, Massachusetts. The term of the lease commenced on September 1, 2017 and will expire on August 31, 2019 . From September 1, 2017 through August 31, 2018, the base rent of the lease is $19,796 per month. From September 1, 2018 until the expiration date, the base rent of the lease will be $20,303 per month. In addition to the base rent, we are also responsible for our share of the operating expenses, utility costs and real estate taxes, in accordance with the terms of the lease. At December 31, 2017 , future minimum payments under the lease are approximately $0.3 million , which is comprised of $0.2 million for the calendar year 2018 and $0.1 million for the calendar year 2019. Rent expense of $0.4 million , $3.2 million and $4.6 million was incurred during the years ended December 31, 2017 , 2016 and 2015 , respectively. We terminated our previous lease for office space at 784 Memorial Drive effective August 31, 2017. See Note 7 for details of the previous lease. We terminated our previous lease for laboratory and office space at 780 Memorial Drive and 790 Memorial Drive effective October 31, 2016. As a result of our early termination, we paid our landlord a termination payment of approximately $1.8 million in November 2016.

Collaborations

Collaborations	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Collaborations	11. Collaborations Takeda In July 2010, we entered into a development and license agreement with Intellikine, Inc., or Intellikine, under which we obtained rights to discover, develop and commercialize pharmaceutical products targeting the delta and/or gamma isoforms of phosphoinositide-3-kinase, or PI3K, including IPI-549 and duvelisib, an oral, dual inhibitor of PI3K delta and gamma. In January 2012, Intellikine was acquired by Takeda Pharmaceutical Company Limited. We refer to our PI3K inhibitor program licensor as Takeda. In December 2012, we amended and restated our development and license agreement with Takeda and further amended the agreement in July 2014, September 2016 and July 2017. We refer to the amended and restated development and license agreement, as amended, as the Takeda Agreement. Under the terms of the December 2012 amendment to the Takeda Agreement, we retained worldwide development rights for, and, in exchange for an agreement to pay Takeda $15.0 million in installments, we regained commercialization rights for products arising from the agreement for all therapeutic indications. We are solely responsible for research conducted under the agreement. During the year ended December 31, 2012, we paid $1.7 million of the $15.0 million , and we recorded the $15.0 million release payment at its fair value of $14.4 million in research and development expenses. During the year ended December 31, 2014, we paid to Takeda the second installment of $6.7 million . During the year ended December 31, 2015, we paid to Takeda the final installment of $6.7 million . Under the terms of the Takeda Agreement, we are obligated to pay Takeda up to $5.0 million in remaining success-based milestone payments for the development of a product candidate other than duvelisib, which could include IPI-549. We are also obligated to pay Takeda up to $165.0 million in remaining success-based milestone payments related to the approval and commercialization of one product candidate other than duvelisib, which could be IPI-549. Due to amendments to the Takeda Agreement described below, we are no longer obligated to pay Takeda royalties on net sales of IPI-549, other products containing a selective inhibitor of PI3K-gamma, or duvelisib in oncology indications. However, we remain obligated to pay Takeda tiered royalties ranging from 7% to 11% on worldwide net sales of products containing a selective inhibitor of PI3K-delta or a selective dual inhibitor of PI3K delta and gamma, as described in the Takeda Agreement, including duvelisib if commercialized outside oncology indications. Such royalties are payable until the later to occur of (i) the expiration of specified patent rights and (ii) the expiration of non-patent regulatory exclusivities in a country, subject to reduction of the royalties and, in certain circumstances, limits on the number of products subject to a royalty obligation. Under the September 2016 amendment to the Takeda Agreement, and in connection with our entry into the Verastem Agreement described below, we are no longer obligated to pay Takeda any remaining milestone payments for the development, approval or commercialization of duvelisib. In return, we are obligated to pay Takeda 50% of all revenue arising from certain qualifying transactions for duvelisib, including those under the Verastem Agreement, described in more detail below, subject to certain exceptions including revenue we receive as reimbursement for duvelisib research and development expenses. Under the July 2014 amendment to the Takeda Agreement, we paid a $52.5 million fee on March 31, 2015 to exercise an option that we purchased from Takeda in July 2014. As a result of our exercise of this option, we are no longer obligated under the Takeda Agreement to pay to Takeda tiered royalties with respect to worldwide net sales in oncology indications of products containing or comprised of duvelisib. We recognized the $52.5 million exercise payment as research and development expense during the year ended December 31, 2015 as there is no alternative future use beyond the existing research and development activities. The July 2017 amendment to the Takeda Agreement terminated our obligations to pay royalties to Takeda with respect to worldwide net sales of products containing or comprised of a selective inhibitor of PI3K gamma, including but not limited to IPI-549. In consideration for such termination, we concurrently executed a convertible promissory note, which we refer to as the Takeda Note, pursuant to which we are obligated to pay Takeda, or its designated affiliate, the principal amount of $6.0 million together with interest accruing at a rate of 8% per annum on or before July 26, 2018 in cash or in shares of our common stock, at the election of Takeda. The $6.0 million has been included in our accompanying consolidated balance sheets as a current liability titled Note Payable. For the year ended December 31, 2017 , we recorded the $6.0 million in research and development expense and $0.2 million of interest expense related to the Takeda Note. On March 12, 2018, we exercised our right to prepay in full the Takeda Note in the principal amount of $6.0 million together with interest of approximately $0.3 million . Takeda elected to receive $4.0 million of such payment in cash and approximately $2.3 million of such payment in shares of our common stock. Pursuant to the terms of the Takeda Note, we issued 1,134,689 shares of common stock to Takeda at a price of $2.028 per share. The Takeda Agreement expires on the later of the expiration of certain patents and the expiration of the royalty payment terms for the products, unless earlier terminated in accordance with its terms. Either party may terminate the Takeda Agreement on 75 days ’ prior written notice if the other party materially breaches the agreement and fails to cure such breach within the applicable notice period, provided that the notice period is reduced to 30 days where the alleged breach is non-payment. Takeda may also terminate the Takeda Agreement if we are not diligent in developing or commercializing the licensed products and do not, within three months after notice from Takeda, demonstrate to Takeda’s reasonable satisfaction that we have not failed to be diligent. The foregoing periods are subject to extension in certain circumstances. Additionally, Takeda may terminate the Takeda Agreement upon 30 days ’ prior written notice if we or a related party bring an action challenging the validity of any of the licensed patents, provided that we have not withdrawn such action before the end of the 30 -day notice period. We may terminate the agreement at any time upon 180 days ’ prior written notice. The Takeda Agreement also provides for customary reciprocal indemnification obligations of the parties. Verastem On October 29, 2016, we and Verastem entered into a license agreement, which we and Verastem amended and restated on November 1, 2016, effective as of October 29, 2016. We refer to the amended and restated license agreement as the Verastem Agreement. Under the Verastem Agreement, we granted to Verastem an exclusive worldwide license for the research, development, commercialization, and manufacture of duvelisib and products containing duvelisib, which we refer to as the Licensed Products, in each case in oncology indications. Upon entry into the Verastem Agreement, Verastem assumed financial responsibility for activities that were part of our ongoing duvelisib program, including a randomized, Phase 3 monotherapy clinical study in patients with relapsed or refractory chronic lymphocytic leukemia or small lymphocytic lymphoma which we refer to as the DUO Study. Verastem is obligated to use diligent efforts, as defined in the Verastem Agreement, to develop and commercialize one Licensed Product. During the term of the Verastem Agreement, we have agreed not to research, develop, manufacture or commercialize duvelisib in any indication in humans or animals. Under the Verastem Agreement, we have financial responsibility for up to $4.5 million of costs related to the shutdown of certain specified clinical studies. We have incurred the $4.5 million maximum for clinical study shutdown costs through December 31, 2017. Following a short transition period, which terminated December 31, 2016, Verastem assumed all financial and operational responsibility for the duvelisib program except for the clinical shutdown costs and certain clinical close-out activities that we agreed to retain. Verastem will reimburse us for certain prepaid expenses and costs incurred by us during the transition period associated with the clinical studies assumed by Verastem. As of December 31, 2016, we recognized a receivable from Verastem of $4.4 million within prepaid expenses and other current assets that represents reimbursements of our transition activities as well as clinical prepaid expenses that are being assumed by Verastem. We received the reimbursements during the year ended December 31, 2017. During the year ended December 31, 2016, we recognized a credit to research and development expense of $3.3 million , a credit of $0.4 million to general and administrative expense and the remainder related to existing clinical prepaid expenses. On September 6, 2017, Verastem notified us that the DUO Study met certain pre-specified criteria at completion triggering a $6.0 million payment under the Verastem Agreement, which we received in cash on October 13, 2017. We recorded this $6.0 million payment as revenue during the year ended December 31, 2017 . On February 7, 2018, Verastem announced it had submitted a new drug application, or NDA, to the U.S. Food and Drug Administration, or FDA, for approval of duvelisib for the treatment of patients with relapsed or refractory chronic lymphocytic leukemia/small lymphocytic lymphoma and accelerated approval for the treatment of relapsed or refractory follicular lymphoma. If Verastem receives approval of its NDA for duvelisib, Verastem is required to make a $22.0 million payment to us, in cash or, at Verastem’s election, in whole or in part, in shares of Verastem common stock. For any portion of the remaining payment that Verastem elects to pay in shares of Verastem common stock in lieu of cash, the number of shares of Verastem common stock to be issued would be determined by multiplying (1) 1.025 by (2) the number of shares of common stock equal to (a) the amount of the payment to be paid in shares of common stock divided by (b) the average closing price of a share of common stock as quoted on Nasdaq for a 20 -day period following the public announcement of the applicable event. The shares of common stock would be issued as unregistered securities, and Verastem would have an obligation to promptly file a registration statement with the U.S. Securities and Exchange Commission, or SEC, to register such shares for resale. Any issuance of shares would be subject to the satisfaction of standard closing conditions, including that all material authorizations, consents, and similar approvals necessary for such issuance shall have been obtained. Verastem is also obligated to pay us royalties on worldwide net sales of Licensed Products ranging from the mid-single digits to the high-single digits, which, if received, we expect to share equally with Takeda. The royalty obligation will continue on a product-by-product and country-by-country basis until the latest to occur of (i) the last-to-expire patent right covering the applicable Licensed Product in the applicable country, (ii) the last-to-expire patent right covering the manufacture of the applicable Licensed Product in the country of manufacture of such Licensed Product, (iii) the expiration of non-patent regulatory exclusivity for such Licensed Product in the applicable country and (iv) ten years following the first commercial sale of a Licensed Product in the applicable country, provided that upon the expiration of the last-to-expire patent right covering the Licensed Product in the United States, the applicable royalty on net sales for such Licensed Product in the United States will be reduced by 50% . The royalties are also subject to reduction by 50% of certain third-party royalty payments or patent litigation damages or settlements which might be required to be paid by Verastem if litigation were to arise, with any such reductions capped at 50% of the amounts otherwise payable during the applicable royalty payment period. In addition to the foregoing, Verastem is obligated to pay us a royalty of 4% on worldwide net sales of Licensed Products to cover the reimbursement of research and development costs owed by us to Mundipharma International Corporation Limited, or Mundipharma, and Purdue Pharmaceutical Products L.P., or Purdue. We refer to these royalty obligations as the Trailing Mundipharma Royalties. Once we have fully reimbursed Mundipharma and Purdue, the Trailing Mundipharma Royalties will be reduced to 1% of net sales in the United States. The Trailing Mundipharma Royalties are payable on a product-by-product basis until the latest to occur of (i) the last-to-expire patent right covering the applicable Licensed Product in the United States, (ii) the last-to-expire patent right covering the manufacture of the applicable Licensed Product in the country of manufacture of such Licensed Product, (iii) the expiration of non-patent regulatory exclusivity for such Licensed Product in the United States and (iv) ten years following the first commercial sale of such Licensed Product in the United States, provided that, upon the expiration of the last-to-expire patent right covering a Licensed Product in the United States, the applicable royalty on net sales for such Licensed Product in the United States will be reduced by 50% . In addition, the Trailing Mundipharma Royalties are subject to reduction by 50% of certain third-party royalty payments or patent litigation damages or settlements which might be required to be paid by Verastem if litigation were to arise, with any such reductions capped at 50% of the amounts otherwise payable during the applicable royalty payment period. The Verastem Agreement expires when each party no longer has any obligations to the other party under the Verastem Agreement. Verastem has the right to terminate the Verastem Agreement upon at least 180 days’ prior written notice to us at any time. Either party may terminate the Verastem Agreement if the other party materially breaches or defaults in the performance of its obligations. If we terminate the Verastem Agreement for Verastem’s material breach, patent challenge, or insolvency, or if Verastem terminates for convenience, then, at our request and subject to our execution of a waiver of certain types of damages, Verastem will transition the duvelisib program back to us at Verastem’s cost. If Verastem terminates for our breach or insolvency, Verastem will effect a more limited transition of the duvelisib program to us at our request and cost, subject to our execution of a waiver of certain types of damages, and we will thereafter pay to Verastem a low single-digit royalty on net sales of Licensed Products. We and Verastem have made customary representations and warranties and have agreed to certain customary covenants, including confidentiality and indemnification. PellePharm In June 2013, we entered into a license agreement with PellePharm, Inc., or PellePharm, under which we granted PellePharm exclusive global development and commercialization rights to our hedgehog inhibitor program, including IPI-926, a clinical-stage product candidate. We refer to our license agreement with PellePharm as the PellePharm Agreement and products covered by the PellePharm Agreement as Hedgehog Products. Under the PellePharm Agreement, PellePharm is obligated to pay us up to $11.0 million in success-based milestone payments through the first commercial sale of a Hedgehog Product. PellePharm is also obligated to pay us up to $37.5 million in success-based milestone payments upon the achievement of certain annual net sales thresholds, as well as a share of certain revenue received by PellePharm in the event that PellePharm sublicenses its rights under the PellePharm Agreement. PellePharm is also obligated to pay us tiered royalties on annual net sales of Hedgehog Products, which are subject to reduction after a certain aggregate funding threshold has been achieved. PellePharm’s royalty obligations to us expire on a country-by-country and Hedgehog Product-by-Hedgehog Product basis, and the PellePharm Agreement expires upon the expiration of the last royalty obligation owed by PellePharm to us, at which time the license to Hedgehog Products and licenses to our know-how as described in the PellePharm Agreement become fully-paid-up and non-royalty-bearing licenses. PellePharm has the right to terminate the PellePharm Agreement upon at least 180 days’ prior written notice to us at any time, and we may terminate the PellePharm Agreement if PellePharm puts forth or actively assists a patent challenge related to our Hedgehog Product patent rights. Either party may terminate the PellePharm Agreement if the other party materially breaches or defaults in the performance of its obligations. Upon termination by either party, all rights and licenses granted by us to PellePharm under the PellePharm Agreement terminate and PellePharm shall, to the extent applicable, transfer and assign to us all rights, title, and interest in and to the trademark(s) used for Hedgehog Products in the Territory. We and PellePharm have made customary representations and warranties and have agreed to certain customary covenants, including confidentiality and indemnification. AbbVie On September 2, 2014, we entered into a collaboration and license agreement with AbbVie which we refer to as the AbbVie Agreement. Under the AbbVie Agreement, we and AbbVie agreed to develop and commercialize products containing duvelisib in oncology indications. We refer to products containing duvelisib as Duvelisib Products. IPI-549 was excluded from the collaboration. On June 24, 2016, AbbVie delivered to us a written notice that AbbVie was exercising its right to terminate the AbbVie Agreement unilaterally upon 90 days ’ written notice, which we refer to as the AbbVie Opt-Out. The termination of the AbbVie Agreement was effective on September 23, 2016. The AbbVie Opt-Out was irrevocable, and we had no obligation to continue to provide AbbVie any services related to Duvelisib Products after June 24, 2016. We recognized revenue of $18.7 million during the year ended December 31, 2016 related to the license and development and committee services provided through June 24, 2016. We recorded the remaining amounts already received from AbbVie and allocated to development and committee services of $112.2 million as a gain during the year ended December 31, 2016, reflecting the fact that we are no longer obligated to provide any such services and have no obligation to refund any of the payments received to date. Under the terms of the AbbVie Agreement, we and AbbVie agreed to share equally commercial profits or losses of Duvelisib Products in the United States, and AbbVie agreed to pay us tiered royalties on net sales of Duvelisib Products outside the United States. We and AbbVie shared oversight of development and agreed to use diligent efforts, as defined in the AbbVie Agreement, to carry out our development activities under an agreed upon development plan. We had primary responsibility for the conduct of development of Duvelisib Products and had the initial responsibility to manufacture Duvelisib Products. AbbVie had responsibility for the conduct of certain contemplated combination clinical studies, which we refer to as the AbbVie Studies. Excluding the AbbVie Studies, we were responsible for all costs to develop and manufacture Duvelisib Products up to a maximum amount of $667 million . The development and manufacturing costs for the AbbVie Studies were shared equally. During the year ended December 31, 2017 , we did no t recognize any expense related to shared costs with AbbVie. During the year ended December 31, 2016, we recognized an expense of $9.5 million in research and development expense related to our portion of the shared costs. We and AbbVie shared operational responsibility and decision making authority for commercialization of Duvelisib Products in the United States. Prior to commercialization and regulatory approval, we recognized the cost of manufacturing as a component of research and development and the cost of commercialization as a component of general and administrative expenses. During the year ended December 31, 2016 , we accounted for AbbVie’s share of the costs as a reduction of the related expense. We recognized a credit of $1.0 million in research and development expense related to these costs during the year ended December 31, 2016. During the year ended December 31, 2016, we recognized a credit of $4.4 million in general and administrative expense related to these costs. Under the AbbVie Agreement, AbbVie paid us a non-refundable $275 million upfront payment in 2014 and a $130 million milestone payment in November 2015 associated with the completion of enrollment of DYNAMO ™ , our Phase 2 clinical study evaluating the efficacy and safety of duvelisib in patients with refractory indolent non-Hodgkin lymphoma, or iNHL. Of the total $405 million received from AbbVie, we allocated $234.3 million to the license which was recognized as revenue upon receipt of the upfront payment and achievement of the milestone payment. Revenue related to development services and committee services was recognized using the proportionate performance method. On September 23, 2016, the effective date of the AbbVie Agreement termination, we received all rights to the regulatory filings related to duvelisib, our license to AbbVie terminated, and AbbVie granted us an exclusive, perpetual, irrevocable, royalty-free license, under certain patent rights and know-how controlled by AbbVie, to develop, manufacture and commercialize products containing duvelisib, excluding any compound which is covered by patent rights controlled by AbbVie or its affiliates, in oncology indications worldwide. Neither party has any ongoing financial obligation to the other party under the AbbVie Agreement.

Organizational Restructuring

Organizational Restructuring	12 Months Ended
	Dec. 31, 2017
Restructuring and Related Activities [Abstract]
Organizational Restructuring	12. Organizational Restructuring In June 2016, we reported top line data from DYNAMO. The study met its primary endpoint with an overall response rate of 46% , all of which were partial responses, among 129 patients with iNHL. As a result, we commenced the first of four restructurings that were approved by our Board of Directors in order to preserve our resources as we determined future strategic plans. We undertook the second restructuring following the AbbVie Opt-Out and undertook the third and fourth restructurings in connection with progress on our strategic plans to divest duvelisib, ultimately culminating with our entry into the Verastem Agreement. See Note 11 for additional detail on the AbbVie Opt-Out and the Verastem Agreement. We reduced our employee headcount by approximately 75% compared to our employee headcount as of December 31, 2015 due to these four restructurings. We have existing severance plans that outline contractual termination benefits. We recognized all contractual severance and benefits outlined in the plan when termination was probable and reasonably estimable in accordance with FASB Accounting Standards Codification Topic 712, Compensation - Nonretirement Postemployment Benefits , during 2016 at the time of each restructuring. In addition to the employee-related costs, during the year ended December 31, 2016, we recorded approximately $1.9 million of expense related to the write-off of prepaid expenses that were not expected to continue and other payments that were due as a result of early terminations. During the year ended December 31, 2016, we also identified and recorded the impairment of approximately $0.4 million in furniture and fixtures and $0.8 million related to a facility lease that was terminated in 2016. The following table summarizes the impact of the 2016 restructuring activities on our operating expenses and payments for the year ended December 31, 2017 and the current liability remaining on our balance sheet as of December 31, 2017 , in thousands: Amounts accrued at December 31, 2016 Charges incurred during the year ended December 31, 2017 Amounts paid during the year ended December 31, 2017 Less non-cash charges during the year ended December 31, 2017 Amounts accrued at December 31, 2017 (in thousands) Employee severance, benefits and related costs for work force reduction $ 6,892 $ — $ 6,627 $ 265 $ — Contract termination, prepaid expense write-offs and other related costs 28 15 43 — — Total restructuring $ 6,920 $ 15 $ 6,670 $ 265 $ — During the year ended December 31, 2016, we recorded $21.2 million of expense related to restructuring activities of which $13.6 million is recorded in research and development expense and $7.6 million is recorded in general and administrative expense. As of December 31, 2017, we do no t have any future payments or expect to incur any additional costs relating to the restructurings.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	13. Income Taxes We recognized an income tax benefit of $0.7 million for the year ended December 31, 2017 as a result of monetizing our alternative minimum tax credit carryforwards as permitted by the Tax Cut and Jobs Act, or the Act, that was enacted on December 22, 2017. We did no t have any income tax expense for the year ended December 31, 2016, and our income tax expense of $0.3 million for the year ended December 31, 2015, consisted primarily of current U.S. federal taxes. Our income tax expense for the years ended December 31, 2017 , 2016 and 2015 differed from the expected U.S. federal statutory income tax expense as set forth below: Years Ended December 31, 2017 2016 2015 (in thousands) Expected federal tax benefit $ (14,467 ) $ (10,234 ) $ (43,534 ) Permanent differences 673 1,749 2,263 State taxes, net of the deferred federal benefit (2,150 ) (1,589 ) (6,762 ) Tax credit carryforwards — (37 ) (2,735 ) Adjustments to deferred tax assets and deferred tax liabilities 5,291 121 (1,267 ) Alternative minimum tax — — 321 Tax Cut and Jobs Act impact 74,455 — — Other — 79 29 Change in valuation allowance (64,522 ) 9,911 52,020 Income tax expense (benefit) $ (720 ) $ — $ 335 The Act reduces the US federal corporate tax rate from 35% to 21%, effective for tax years including or commencing January 1, 2018. On December 22, 2017, the SEC staff issued Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act, or SAB 118, which allows the recording of provisional amounts during a measurement period not to extend beyond one year of the enactment date. In accordance with SAB 118, we have determined that our deferred tax asset value and associated valuation allowance reduction of $74.5 million is a provisional amount and a reasonable estimate at December 31, 2017. As noted above, there is a $0.7 million tax benefit as a result of monetizing the alternative minimum tax credit carryforwards. The Tax Cut and Jobs Act impact line in the income tax expense reconciliation table above includes tax expense of $75.2 million from the re-measurement of our deferred tax assets offset by tax benefit of $0.7 million as a result of monetizing the alternative minimum tax credit carryforwards. The final impact may differ from this provisional amount due to, among other things, changes in interpretations and assumptions we have made thus far and the issuance of additional regulatory or other guidance. We expect to complete the final impact within the measurement period. The significant components of our deferred tax assets and liabilities are as follows: Years Ended December 31, 2017 2016 (in thousands) Deferred tax assets (liabilities): Net operating loss carryforwards $ 135,787 $ 178,125 Tax credit carryforwards 40,539 40,051 Intangible assets 22,206 32,199 Accrued expenses 88 822 Stock-based compensation 6,056 11,974 Other 391 (377 ) Valuation allowance (205,067 ) (262,794 ) Net deferred tax assets $ — $ — We have recorded a valuation allowance against our deferred tax assets in each of the years ended December 31, 2017 , 2016 and 2015 because management believes that it is more likely than not that these assets will not be realized. The valuation allowance decreased by approximately $57.7 million during the year ended December 31, 2017 primarily as a result of the re-measurement of our deferred tax balance following the Act. The valuation allowance increased by approximately $9.9 million during the year ended December 31, 2016 primarily as a result of the increase in our unbenefited net operating loss deferred tax asset. The valuation allowance increased by approximately $52.0 million during the year ended December 31, 2015 primarily as a result of unbenefited deferred tax assets such as deferred revenue and intangible assets. Subject to the limitations described below, at December 31, 2017 , we have cumulative net operating loss carryforwards of approximately $524.1 million and $407.3 million available to reduce federal and state taxable income, which expire through 2037 , and have begun to expire and will continue to expire through 2037 , respectively. In addition, we have cumulative federal and state tax credit carryforwards of $32.5 million and $10.2 million , respectively, available to reduce federal and state income taxes which expire through 2036 and 2030 , respectively. Our net operating loss carryforwards and tax credit carryforwards are limited as a result of certain ownership changes, as defined under Sections 382 and 383 of the Internal Revenue Code. This limits the annual amount of these tax attributes that can be utilized to offset future taxable income or tax liabilities. The amount of the annual limitation is determined based on our value immediately prior to an ownership change. Subsequent ownership changes may affect the limitation in future years. The net operating losses and tax credit carryforwards that have and will expire unused in the future as a result of Section 382 and 383 limitations have been excluded from the amounts disclosed above. At December 31, 2017 and 2016 , we had no unrecognized tax benefits. As of December 31, 2017 , 2016 and 2015 , we had no accrued interest or penalties related to uncertain tax positions and no amounts have been recognized in our consolidated statements of operations. We will recognize interest and penalties related to uncertain tax positions in income tax expense. For all years through December 31, 2016, we generated research credits but have not conducted a study to document the qualified activities. This study may result in an adjustment to our research and development credit carryforwards; however, until a study is completed and any adjustment is known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against our research and development credits and, if an adjustment is required, this adjustment would be offset by an adjustment to the deferred tax asset established for the research and development credit carryforwards and the valuation allowance. We file income tax returns in the U.S. federal, Massachusetts, and other state jurisdictions. The statute of limitations for assessment by the Internal Revenue Service, or IRS, and state tax authorities is closed for tax years prior to 2014, although carryforward attributes that were generated prior to tax year 2014 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.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Stockholders' Equity	14. Stockholders’ Equity Warrants On February 24, 2014, we entered into a facility agreement with affiliates of Deerfield Management Company, L.P., or Deerfield. In connection with the execution of the original facility agreement, we issued to Deerfield warrants to purchase an aggregate of 1,000,000 shares of common stock at an exercise price of $13.83 per share. The warrants have dividend rights to the same extent as if the warrants were exercised into shares of common stock. The warrants expire on the seventh anniversary of their issuance and contain certain limitations that prevent the holder from acquiring shares upon exercise of a warrant that would result in the number of shares beneficially owned by the holder exceeding 9.985% of the total number of shares of common stock then issued and outstanding. As of December 31, 2017 , no warrants have been exercised.

Defined Contribution Benefit Pl

Defined Contribution Benefit Plan	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Defined Contribution Benefit Plan	15. Defined Contribution Benefit Plan We sponsor a 401(k) retirement plan in which substantially all of our full-time employees are eligible to participate. Participants may contribute a percentage of their annual compensation to this plan, subject to statutory limitations. During the years ended December 31, 2017 , 2016 and 2015 , we matched 50% of the participant’s contribution up to 6% of the participant’s pre-tax salary with shares of our common stock. Our matching contributions during the year ended December 31, 2017 , 2016 and 2015 were $0.1 million , $0.8 million and $0.9 million , respectively.

Quarterly Financial Information

Quarterly Financial Information (unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information (unaudited)	16. Quarterly Financial Information (unaudited) Quarter Ended Quarter Ended Quarter Ended Quarter Ended (in thousands, except shares and per share amounts) Collaboration revenue $ — $ — $ 6,000 $ — Operating expenses: Research and development 4,039 3,901 9,338 3,552 General and administrative 6,437 6,205 4,505 4,468 Total operating expenses 10,476 10,106 13,843 8,020 Loss from operations (10,476 ) (10,106 ) (7,843 ) (8,020 ) Other income (expenses): Interest expense (302 ) (300 ) (287 ) (121 ) Other expense (note 7) — (6,882 ) — — Investment and other income 303 334 1,026 124 Total other income (expense) 1 (6,848 ) 739 3 Loss before income taxes (10,475 ) (16,954 ) (7,104 ) (8,017 ) Income taxes benefit — — — 720 Net loss $ (10,475 ) $ (16,954 ) $ (7,104 ) $ (7,297 ) Basic and diluted loss per common share: $ (0.21 ) $ (0.34 ) $ (0.14 ) $ (0.14 ) Basic and diluted weighted average number of common shares outstanding: 50,423,353 50,455,832 50,635,828 50,721,658 Quarter Ended Quarter Ended Quarter Ended Quarter Ended (in thousands, except shares and per share amounts) Collaboration revenue $ 9,256 $ 9,467 $ — $ — Operating expenses: Research and development 39,188 52,947 12,814 14,662 General and administrative 10,836 15,692 7,120 8,571 Total operating expenses 50,024 68,639 19,934 23,233 Gain on AbbVie Opt-Out (note 12) — 112,216 — — Income (loss) from operations (40,768 ) 53,044 (19,934 ) (23,233 ) Other income (expenses): Interest expense (309 ) (307 ) (305 ) (304 ) Interest and investment income (loss) 413 254 741 607 Total other income (expense) 104 (53 ) 436 303 Net income (loss) $ (40,664 ) $ 52,991 $ (19,498 ) $ (22,930 ) Income (loss) per common share: Basic $ (0.82 ) $ 1.05 $ (0.39 ) $ (0.46 ) Diluted $ (0.82 ) $ 1.05 $ (0.39 ) $ (0.46 ) Weighted average number of common shares outstanding: Basic 49,339,888 49,437,062 49,583,776 50,099,153 Diluted 49,339,888 49,439,537 49,583,776 50,099,153

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	17. Subsequent Events Takeda On March 12, 2018, we exercised our right to prepay in full the Takeda Note in the principal amount of $6.0 million together with interest of approximately $0.3 million . Takeda elected to receive $4.0 million of such payment in cash and approximately $2.3 million of such payment in shares of our common stock. Pursuant to the terms of the Takeda Note, we issued 1,134,689 shares of common stock to Takeda at a price of $2.028 per share. At-the-Market Facility In May 2016, we entered into an at-the-market sales agreement, or Sales Agreement, with Cantor Fitzgerald & Co., or Cantor Fitzgerald pursuant to which we may from time to time, at our option, offer and sell shares of our common stock having an aggregate offering price of up to $50 million through Cantor Fitzgerald, acting as our sales agent. Cantor Fitzgerald will be entitled to a commission of 3.0% of the aggregate gross proceeds from sales of shares of our common stock under the Sales Agreement. Sales of shares of our common stock under the Sales Agreement may be made by any method permitted by law that is deemed an “at the market” offering as defined in Rule 415 under the Securities Act of 1933, as amended, including sales made through the Nasdaq Global Select Market, on any other existing trading market for our common stock or to or through a market maker. We may also authorize Cantor Fitzgerald to sell shares in privately negotiated transactions. As of March 14, 2018, we sold 950,407 shares at a weighted average price per share of $2.15 under the at-the-market facility for an additional $2.0 million in net proceeds. We have no obligation to sell shares of our common stock and cannot provide any assurances that we will issue any additional shares pursuant to the Sales Agreement. We may also suspend the offering of shares of our common stock upon notice and subject to other conditions.

Summary of Significant Accoun24

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation These consolidated financial statements include the accounts of Infinity and its wholly-owned subsidiaries. We have eliminated all significant intercompany accounts and transactions in consolidation. The preparation of consolidated financial statements in accordance with generally accepted accounting principles requires our management to make estimates and judgments that may affect the reported amounts of assets, liabilities, revenues and expenses, and related disclosure of contingent assets and liabilities. On an ongoing basis, we evaluate our estimates and judgments. We base our estimates on historical experience and on various other assumptions that are believed to be reasonable, the results of which form the basis for making judgments about the carrying values of assets and liabilities. Actual results may differ from these estimates under different assumptions or conditions.
Cash Equivalents and Available-For-Sale Securities	Cash Equivalents and Available-For-Sale Securities Cash equivalents and available-for-sale securities primarily consist of money market funds and U.S. government-sponsored enterprise obligations. We consider all highly liquid investments with maturities of three months or less at the time of purchase to be cash equivalents. Cash equivalents, which consist of money market funds, corporate obligations and U.S. government-sponsored enterprise obligations, are stated at fair value. They are also readily convertible to known amounts of cash and have such short-term maturities that each presents insignificant risk of change in value due to changes in interest rates. Our classification of cash equivalents is consistent with prior periods. We determine the appropriate classification of marketable securities at the time of purchase and reevaluate such designation at each balance sheet date. We have classified all of our marketable securities at December 31, 2017 and 2016 as “available-for-sale.” We carry available-for-sale securities at fair value, with the unrealized gains and losses reported in accumulated other comprehensive income (loss), which is a separate component of stockholders’ equity. We adjust the cost of available-for-sale debt securities for amortization of premiums and accretion of discounts to maturity. We include such amortization and accretion in investment and other income. The cost of securities sold is based on the specific identification method. We include in investment income interest and dividends on securities classified as available-for-sale. We conduct periodic reviews to identify and evaluate each investment that is in an unrealized loss position in order to determine whether an other-than-temporary impairment exists. An unrealized loss exists when the current fair value of an individual security is less than its amortized cost basis. Unrealized losses on available-for-sale debt securities that are determined to be temporary, and not related to credit loss, are recorded, net of tax, in accumulated other comprehensive income (loss). For available-for-sale debt securities in an unrealized loss position, we perform an analysis to assess whether we intend to sell or whether we would more likely than not be required to sell the security before the expected recovery of the amortized cost basis. Where we intend to sell a security, or may be required to do so, the security’s decline in fair value is deemed to be other-than-temporary, and the full amount of the unrealized loss is recorded within earnings as an impairment loss. Regardless of our intent to sell a security, we perform additional analysis on all securities in an unrealized loss position to evaluate losses associated with the creditworthiness of the security. Credit losses are identified where we do not expect to receive cash flows sufficient to recover the amortized cost basis of a security and are recorded within earnings as an impairment loss.
Concentration of Risk	Concentration of Risk Cash and cash equivalents are primarily maintained with two major financial institutions in the United States. Deposits at banks may exceed the insurance provided on such deposits. Generally, these deposits may be redeemed upon demand and, therefore, bear minimal risk. Financial instruments that potentially subject us to concentration of credit risk primarily consist of available-for-sale securities. Available-for-sale securities consist of U.S. Treasury securities and U.S. government-sponsored enterprise obligations. Our investment policy, which has been approved by our Board of Directors, limits the amount that we may invest in any one issuer of investments, thereby reducing credit risk concentrations.
Segment Information	Segment Information We operate in one business segment, which focuses on drug development. We make operating decisions based upon performance of the enterprise as a whole and utilize our consolidated financial statements for decision making.
Property and Equipment	Property and Equipment Property and equipment are stated at cost. Depreciation is recorded using the straight-line method over the estimated useful lives of the applicable assets. Application development costs incurred for computer software developed or obtained for internal use are capitalized. Upon sale or retirement, the cost and related accumulated depreciation are eliminated from the respective account, and the resulting gain or loss, if any, is included in current operations. Amortization of leasehold improvements, building improvements and capital leases is recorded as depreciation expense and included in research and development and general and administrative expense, as applicable. Repairs and maintenance charges that do not increase the useful life of the assets are charged to operations as incurred. Property and equipment are depreciated over the following periods: Computer equipment and software 3 to 5 years Leasehold improvements Shorter of lease term or useful life of asset Building and building improvements 10 to 50 years, less estimated residual Furniture and fixtures 7 to 10 years
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets We evaluate our long-lived assets for potential impairment. Potential impairment is assessed when there is evidence that events or changes in circumstances have occurred that indicate that the carrying amount of a long-lived asset may not be recovered. Recoverability of these assets is assessed based on undiscounted expected future cash flows from the assets, considering a number of factors, including past operating results, budgets and economic projections, market trends and product development cycles. An impairment in the carrying value of each asset is assessed when the undiscounted expected future cash flows, including its eventual residual value, derived from the asset are less than its carrying value. Impairments, if any, are recognized in earnings. An impairment loss would be recognized in an amount equal to the excess of the carrying amount over the undiscounted expected future cash flows.
Fair Value Measurements	Fair Value Measurements We define fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. We determine fair value based on the assumptions market participants use when pricing the asset or liability. We also use the fair value hierarchy that prioritizes the information used to develop these assumptions. We value our available-for-sale securities utilizing third-party pricing services. The pricing services use many observable market inputs to determine value, including benchmark yields, reportable trades, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, reference data, new issue data, monthly payment information and collateral performance. We validate the prices provided by our third-party pricing services by understanding the models used, obtaining market values from other pricing sources and confirming that those securities trade in active markets.
Revenue Recognition	Revenue Recognition To date, all of our revenue has been generated under research collaboration agreements. The terms of these research collaboration agreements may include payment to us of non-refundable, upfront license fees, funding or reimbursement of research and development efforts, milestone payments if specified objectives are achieved, and/or royalties on product sales. We evaluate all deliverables within an arrangement to determine whether or not they provide value on a stand-alone basis. Based on this evaluation, the deliverables are separated into units of accounting. For each unit of accounting identified within an arrangement, we determine the period over which the performance obligation occurs. Revenue is then recognized using the proportional performance method. The proportional performance method is used when the level of effort to complete the performance obligations under an arrangement can be reasonably estimated. We recognize revenue based upon our best estimate of the selling price for each element when there is no other means to determine the fair value of that item and allocate the consideration based on the relative values. The process for determining the best estimate of the selling price involves significant judgment and estimates. At the inception of each agreement that includes milestone payments, we evaluate whether each milestone is substantive on the basis of the contingent nature of the milestone. This evaluation includes an assessment of whether: • the consideration is commensurate with either (1) our performance to achieve the milestone, or (2) the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from our performance to achieve the milestone, • the consideration relates solely to past performance, and • the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. In making this assessment, we evaluate factors such as the clinical, regulatory, commercial and other risks that must be overcome to achieve the respective milestone, the level of effort and investment required, and whether the milestone consideration is reasonable relative to all deliverables and payment terms in the arrangement. We recognize revenues related to substantive milestones in full in the period in which the substantive milestone is achieved. If a milestone payment is not considered substantive, we recognize the amount associated with the applicable milestone based on the period over which the performance obligation occurs for each deliverable in the arrangement. We will recognize royalty revenue, if any, based upon actual and estimated net sales by the licensee of licensed products in licensed territories in the period the sales occur.
Income Taxes	Income Taxes We use the liability method to account for income taxes. Deferred tax assets and liabilities are determined based on differences between financial reporting and income tax basis of assets and liabilities, as well as net operating loss and tax credit carryforwards, and are measured using the enacted tax rates and laws that will be in effect when the differences reverse. Deferred tax assets are reduced by a valuation allowance to reflect the uncertainty associated with their ultimate realization. The effect of a change in tax rate on deferred taxes is recognized in income or loss in the period that includes the enactment date. We use our judgment for the financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. We recognize any material interest and penalties related to unrecognized tax benefits in income tax expense.
Basic and Diluted Net Loss per Common Share	Basic and Diluted Net Loss per Common Share Basic net loss per share is based upon the weighted average number of common shares outstanding during the period, excluding restricted stock that has been issued but has not yet vested. Diluted net loss per share is based upon the weighted average number of common shares outstanding during the period plus the effect of additional weighted average common equivalent shares outstanding during the period when the effect of adding such shares is dilutive. Common equivalent shares result from the assumed exercise of outstanding stock options and the exercise of outstanding warrants (the proceeds of which are then assumed to have been used to repurchase outstanding stock using the treasury stock method) and the vesting of restricted shares of common stock. In addition, the assumed proceeds under the treasury stock method include the average unrecognized compensation expense of stock options that are in-the-money. This results in the “assumed” buyback of additional shares, thereby reducing the dilutive impact of stock options. The two-class method is used for outstanding warrants as such warrants are considered to be participating securities, and such method is more dilutive than the treasury stock method.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is comprised of net loss and other comprehensive income (loss). Other comprehensive income (loss) is comprised of unrealized holding gains and losses arising during the period on available-for-sale securities that are not other-than-temporarily impaired.
Stock-Based Compensation Expense	Stock-Based Compensation Expense For awards granted to employees and directors, including our 2013 Employee Stock Purchase Plan, or ESPP, we measure stock-based compensation cost at the grant date based on the estimated fair value of the award and recognize it as expense over the requisite service period on a straight-line basis. We record the expense of services rendered by non-employees based on the estimated fair value of the stock option as of the respective vesting date. We use the Black-Scholes valuation model in determining the fair value of all equity awards. For awards with performance conditions, we estimate the likelihood of satisfaction of the performance conditions, which affects the period over which the expense is recognized. When the performance conditions related to these awards are determined to be probable, we recognize the expense over the requisite service period.
Research and Development Expense	Research and Development Expense Research and development expense consists of expenses incurred in performing research and development activities, including salaries and benefits, overhead expenses including facilities expenses, materials and supplies, preclinical expenses, clinical trial and related clinical manufacturing expenses, comparator and combination drug expenses, stock-based compensation expense, depreciation of equipment, contract services, and other outside expenses. We also include as research and development expense upfront license payments related to acquired technologies which have not yet reached technological feasibility and have no alternative use. We expense research and development costs as they are incurred. Prepaid comparator and combination drug expenses are capitalized and then recognized as expense when title transfers to us. We have been a party to collaboration agreements in which we were reimbursed for work performed on behalf of the collaborator, as well as one in which we reimbursed the collaborator for work it had performed. We record all appropriate expenses under our collaborations as research and development expense. If the arrangement provides for reimbursement of research and development expenses incurred by us, we evaluate the terms of the arrangement to determine whether the reimbursement should be recorded as revenue or as an offset to research and development expense. If the arrangement provides for us to reimburse the collaborator for research and development expenses or for the achievement of a development milestone for which a payment is due, we record the reimbursement or the achievement of the development milestone as research and development expense.
New Accounting Pronouncements and Recently Adopted Accounting Pronouncements	New Accounting Pronouncements In May 2014, the Financial Accounting Standards Board, or FASB, issued Accounting Standard Update, or ASU, No. 2014-9, Revenue from Contracts with Customers , or ASU No. 2014-9, which supersedes all existing revenue recognition requirements, including most industry-specific guidance. The new standard requires a company to recognize revenue when it transfers goods or services to customers in an amount that reflects the consideration that the company expects to receive for those goods or services. ASU No. 2014-9 was originally effective for interim and annual periods beginning after December 15, 2016. In August 2015, the FASB issued a one-year deferral of the effective date of this standard to annual reporting periods, and interim reporting periods within those years, beginning after December 15, 2017. Entities are allowed to adopt the standard as of the original effective date. The standard allows for two transition methods - full retrospective, in which the standard is applied to each prior reporting period presented or modified retrospective, in which the cumulative effect of initially applying the standard recognized at the date of initial adoption. We elected the modified retrospective approach and adopted the new standard effective January 1, 2018. We have substantially completed our assessment of the standard on our two out-licensing arrangements and do not expect the adoption of the standard to have a material impact on our financial position and results of operations when applied to our out-licensing arrangements. We will complete our assessment in the first quarter of 2018. In February 2016, the FASB issued ASU No. 2016-02, Leases, or ASU No. 2016-02 , which requires lessees to recognize the assets and liabilities arising from leases on the balance sheet. ASU No. 2016-02 is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Early adoption is permitted. We are currently evaluating the method of adoption and the potential impact that ASU No. 2016-02 may have on our financial position and results of operations. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments, or ASU No. 2016-15. The new standard clarifies classification of certain cash receipts and cash payments on the statement of cash flows to reduce existing diversity in practice. The new accounting guidance will be effective on January 1, 2018. The adoption of ASU No. 2016-15 will not have an impact on our consolidated financial statements. In November 2016, FASB issued ASU No. 2016-18, Statement of Cash Flows, Restricted Cash, or ASU No. 2016-18. ASU No. 2016-18 provides guidance on the presentation of restricted cash and restricted cash equivalents in the statement of cash flows. Under ASU No. 2016-18, the statement of cash flows shall explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Amounts generally described as restricted cash and cash equivalents should now be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period amounts shown on the statements of cash flows. The amendments of this ASU are effective for reporting periods beginning after December 15, 2017, with early adoption permitted. Other than the revised statement of cash flows presentation, the adoption of ASU No. 2016-18 will not have an impact on our consolidated financial statements. In May 2017, FASB issued ASU No. 2017-09, Compensation—Stock Compensation: Scope of Modification Accounting, or ASU No. 2017-09. ASU No. 2017-09 clarifies when changes to the terms and conditions of a share-based payment award must be accounted for as modifications. The new guidance will reduce diversity in practice and result in fewer changes to the terms of an award being accounted for as modifications. It does not change the accounting for modifications. ASU No. 2017-09 is effective for reporting periods beginning after December 15, 2017, with early adoption permitted. The adoption of ASU No. 2017-09 will not have an impact on our consolidated financial statements. Recently Adopted Accounting Pronouncements In March 2016, the FASB issued ASU No. 2016-09, Improvements to Employee Share-Based Payment Accounting , or ASU No. 2016-09, which simplifies several aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities and classification of cash flows. We adopted ASU No. 2016-09 as of January 1, 2017. Under the new standard, all excess tax benefits and tax deficiencies are recognized as income tax expense or benefit in the statement of operations. The tax effects of exercised or vested awards are treated as discrete items in the reporting period in which they occur. We applied the modified retrospective adoption approach upon adoption of the standard, and prior periods have not been adjusted. As a result, we established a net operating loss deferred tax asset of $7.5 million to account for prior period excess tax benefits through retained earnings and an offsetting valuation allowance of $7.5 million through retained earnings because it is not more likely than not that the deferred tax asset will be realized due to historical and expected future losses. We elected to recognize forfeitures related to employee share-based payments as they occur. There was not a material impact on our financial statements as a result of the adoption of this guidance.

Summary of Significant Accoun25

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Property and Equipment, Depreciated Periods	Property and equipment are depreciated over the following periods: Computer equipment and software 3 to 5 years Leasehold improvements Shorter of lease term or useful life of asset Building and building improvements 10 to 50 years, less estimated residual Furniture and fixtures 7 to 10 years
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The following outstanding shares of common stock equivalents were excluded from the computation of net loss per share attributable to common stockholders for the periods presented because including them would have been antidilutive: At December 31, 2017 2016 2015 Stock options 7,460,722 6,067,945 8,265,577 Warrants 1,000,000 1,000,000 1,000,000 Unvested restricted stock — 797,111 —

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation Expense, Related to All Equity Awards	Total stock-based compensation expense, related to all equity awards, comprised the following: Year Ended December 31, 2017 2016 2015 (in thousands) Research and development $ 1,756 $ 6,421 $ 8,474 General and administrative 5,216 7,293 6,226 Total stock-based compensation expense $ 6,972 $ 13,714 $ 14,700
Schedule of Restricted Stock Activity	A summary of our restricted stock activity for the year ended December 31, 2017 is as follows: Restricted Stock Weighted-Average Grant-Date Fair Value Unvested at January 1, 2017 797,111 $ 1.43 Granted — — Vested (190,989 ) 1.54 Canceled (606,122 ) 1.40 Unvested at December 31, 2017 — $ —
Fair Value Stock Options, Weighted-Average Assumptions	We estimate the fair value of stock options at the date of grant using the Black-Scholes valuation model with the following weighted-average assumptions: December 31, 2017 2016 2015 Risk-free interest rate 1.9 % 1.8 % 1.5 % Expected annual dividend yield — — — Expected stock price volatility 90.1 % 73.0 % 70.8 % Expected term of options 5.6 years 5.4 years 5.4 years
Summary of Stock Option Activity	A summary of our stock option activity for the year ended December 31, 2017 is as follows: Stock Options Weighted- Average Exercise Price Weighted-Average Remaining Contractual Life (years) Aggregate Intrinsic Value (in millions) Outstanding at January 1, 2017 6,067,945 $ 12.06 Granted 4,796,500 1.61 Exercised — — Forfeited (3,403,723 ) 10.57 Outstanding at December 31, 2017 7,460,722 $ 6.02 7.2 $ 2.0 Exercisable at December 31, 2017 3,028,913 $ 11.53 4.8 $ 0.2
Fair Value Employee Stock Purchase Plan, Weighted-Average Assumptions	For the years ended December 31, 2017 , 2016 and 2015 , the fair values were estimated using the Black-Scholes valuation model using the following weighted-average assumptions: Year Ended December 31, 2017 2016 2015 Risk-free interest rate 1.2 % 0.8 % 0.4 % Expected annual dividend yield — — — Expected stock price volatility 102.3 % 63.5 % 60.3 % Expected term of options 1.25 years 1.25 years 1.25 years

Cash, Cash Equivalents and Av27

Cash, Cash Equivalents and Available-for-Sale Securities (Tables)	12 Months Ended
	Dec. 31, 2017
Cash and Cash Equivalents [Abstract]
Summary of Cash, Cash Equivalents and Available-for-sale Securities	The following is a summary of cash, cash equivalents and available-for-sale securities: December 31, 2017 Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value (in thousands) Cash and cash equivalents $ 34,607 $ — $ — $ 34,607 Available-for-sale securities: U.S. Treasury securities due in one year or less 3,497 — (3 ) 3,494 U.S. government-sponsored enterprise obligations due in one year or less 19,520 — (12 ) 19,508 Total available-for-sale securities 23,017 — (15 ) 23,002 Total cash, cash equivalents and available-for-sale securities $ 57,624 $ — $ (15 ) $ 57,609 December 31, 2016 Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value (in thousands) Cash and cash equivalents $ 74,060 $ — $ — $ 74,060 Available-for-sale securities: U.S. Treasury securities due in one year or less 6,753 — (1 ) 6,752 U.S. government-sponsored enterprise obligations due in one year or less 11,254 — (2 ) 11,252 Total available-for-sale securities 18,007 — (3 ) 18,004 Total cash, cash equivalents and available-for-sale securities $ 92,067 $ — $ (3 ) $ 92,064

Fair Value (Tables)

Fair Value (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Assets Carried at Fair Value Measured on Recurring Basis	The following table provides the assets carried at fair value measured on a recurring basis as of December 31, 2017 and 2016 : Level 1 Level 2 (in thousands) December 31, 2017 Assets: Cash and cash equivalents $ 34,607 $ — U.S. Treasury securities — 3,494 U.S. government-sponsored enterprise obligations — 19,508 Total $ 34,607 $ 23,002 December 31, 2016 Assets: Cash and cash equivalents $ 61,008 $ 13,052 U.S. Treasury securities — 6,752 U.S. government-sponsored enterprise obligations — 11,252 Total $ 61,008 $ 31,056

Prepaid Expenses and Other Cu29

Prepaid Expenses and Other Current Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Prepaid Expense and Other Assets, Current [Abstract]
Schedule of Prepaid and Other Current Assets	Prepaid expenses and other current assets consist of the following: December 31, 2017 2016 (in thousands) Prepaid expenses $ 563 $ 3,336 Other current assets 214 5,108 Total prepaid expenses and other current assets $ 777 $ 8,444

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Summary of Property and Equipment	Property and equipment consist of the following: December 31, 2017 2016 (in thousands) Computer equipment and software $ 1,814 $ 4,411 Furniture and fixtures — 918 Building and building improvements — 23,586 Leasehold improvements 16 431 1,830 29,346 Less accumulated depreciation (1,611 ) (5,922 ) $ 219 $ 23,424

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
Accrued Expenses	Accrued expenses consisted of the following: December 31, 2017 2016 (in thousands) Accrued restructuring $ — $ 6,920 Accrued compensation and benefits 2,002 5,445 Accrued clinical and development 1,736 7,367 Other 1,398 1,276 Total accrued expenses $ 5,136 $ 21,008

Organizational Restructuring (T

Organizational Restructuring (Tables)	12 Months Ended
	Dec. 31, 2017
Restructuring and Related Activities [Abstract]
Restructuring and Related Costs	The following table summarizes the impact of the 2016 restructuring activities on our operating expenses and payments for the year ended December 31, 2017 and the current liability remaining on our balance sheet as of December 31, 2017 , in thousands: Amounts accrued at December 31, 2016 Charges incurred during the year ended December 31, 2017 Amounts paid during the year ended December 31, 2017 Less non-cash charges during the year ended December 31, 2017 Amounts accrued at December 31, 2017 (in thousands) Employee severance, benefits and related costs for work force reduction $ 6,892 $ — $ 6,627 $ 265 $ — Contract termination, prepaid expense write-offs and other related costs 28 15 43 — — Total restructuring $ 6,920 $ 15 $ 6,670 $ 265 $ —

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Tax Benefit or Expense	Our income tax expense for the years ended December 31, 2017 , 2016 and 2015 differed from the expected U.S. federal statutory income tax expense as set forth below: Years Ended December 31, 2017 2016 2015 (in thousands) Expected federal tax benefit $ (14,467 ) $ (10,234 ) $ (43,534 ) Permanent differences 673 1,749 2,263 State taxes, net of the deferred federal benefit (2,150 ) (1,589 ) (6,762 ) Tax credit carryforwards — (37 ) (2,735 ) Adjustments to deferred tax assets and deferred tax liabilities 5,291 121 (1,267 ) Alternative minimum tax — — 321 Tax Cut and Jobs Act impact 74,455 — — Other — 79 29 Change in valuation allowance (64,522 ) 9,911 52,020 Income tax expense (benefit) $ (720 ) $ — $ 335
Significant Components of Deferred Tax Assets	The significant components of our deferred tax assets and liabilities are as follows: Years Ended December 31, 2017 2016 (in thousands) Deferred tax assets (liabilities): Net operating loss carryforwards $ 135,787 $ 178,125 Tax credit carryforwards 40,539 40,051 Intangible assets 22,206 32,199 Accrued expenses 88 822 Stock-based compensation 6,056 11,974 Other 391 (377 ) Valuation allowance (205,067 ) (262,794 ) Net deferred tax assets $ — $ —

Quarterly Financial Informati34

Quarterly Financial Information (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information (unaudited)	Quarter Ended Quarter Ended Quarter Ended Quarter Ended (in thousands, except shares and per share amounts) Collaboration revenue $ — $ — $ 6,000 $ — Operating expenses: Research and development 4,039 3,901 9,338 3,552 General and administrative 6,437 6,205 4,505 4,468 Total operating expenses 10,476 10,106 13,843 8,020 Loss from operations (10,476 ) (10,106 ) (7,843 ) (8,020 ) Other income (expenses): Interest expense (302 ) (300 ) (287 ) (121 ) Other expense (note 7) — (6,882 ) — — Investment and other income 303 334 1,026 124 Total other income (expense) 1 (6,848 ) 739 3 Loss before income taxes (10,475 ) (16,954 ) (7,104 ) (8,017 ) Income taxes benefit — — — 720 Net loss $ (10,475 ) $ (16,954 ) $ (7,104 ) $ (7,297 ) Basic and diluted loss per common share: $ (0.21 ) $ (0.34 ) $ (0.14 ) $ (0.14 ) Basic and diluted weighted average number of common shares outstanding: 50,423,353 50,455,832 50,635,828 50,721,658 Quarter Ended Quarter Ended Quarter Ended Quarter Ended (in thousands, except shares and per share amounts) Collaboration revenue $ 9,256 $ 9,467 $ — $ — Operating expenses: Research and development 39,188 52,947 12,814 14,662 General and administrative 10,836 15,692 7,120 8,571 Total operating expenses 50,024 68,639 19,934 23,233 Gain on AbbVie Opt-Out (note 12) — 112,216 — — Income (loss) from operations (40,768 ) 53,044 (19,934 ) (23,233 ) Other income (expenses): Interest expense (309 ) (307 ) (305 ) (304 ) Interest and investment income (loss) 413 254 741 607 Total other income (expense) 104 (53 ) 436 303 Net income (loss) $ (40,664 ) $ 52,991 $ (19,498 ) $ (22,930 ) Income (loss) per common share: Basic $ (0.82 ) $ 1.05 $ (0.39 ) $ (0.46 ) Diluted $ (0.82 ) $ 1.05 $ (0.39 ) $ (0.46 ) Weighted average number of common shares outstanding: Basic 49,339,888 49,437,062 49,583,776 50,099,153 Diluted 49,339,888 49,439,537 49,583,776 50,099,153

Summary of Significant Accoun35

Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands	2 Months Ended	12 Months Ended
	Mar. 14, 2018USD ($)	Dec. 31, 2017USD ($)issuerawardSegmentfinancial_institutionagreementpayment	Jan. 01, 2017USD ($)	Dec. 31, 2016USD ($)
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Cash, cash equivalents and available-for-sale securities		$ 57,624		$ 92,067
Number of major financial institutions | financial_institution		2
Number of issuers of investments | issuer		1
Number of operating segments | Segment		1
Reclassifications out of accumulated other comprehensive income (loss)		$ 0
Number of awards with market conditions | award		0
Number of out-licensing agreements | agreement		2
Net operating loss, deferred tax asset		$ 135,787		178,125
Valuation allowance		$ 205,067		$ 262,794
Accounting Standards Update 2016-09
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Net operating loss, deferred tax asset			$ 7,500
Valuation allowance			$ 7,500
Takeda Agreement | Subsequent Event
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Repayments of debt, cash	$ 4,000
Verastem Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Number of potential milestone payments included in forecast | payment		0
Collaborative agreement payment due upon approval of drug application		$ 22,000
Common Stock | Takeda Agreement | Subsequent Event
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Repayments of debt, including interest, noncash	2,300
At-The-Market Facility | Subsequent Event
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Sale of stock, consideration received on transaction	$ 2,000

Summary of Significant Accoun36

Summary of Significant Accounting Policies - Property and Equipment, Depreciation Periods (Details)	12 Months Ended
	Dec. 31, 2017
Computer equipment and software | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	3 years
Computer equipment and software | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years
Building and building improvements | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	10 years
Building and building improvements | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	50 years
Furniture and fixtures | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	7 years
Furniture and fixtures | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	10 years

Summary of Significant Accoun37

Summary of Significant Accounting Policies - Antidilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	7,460,722	6,067,945	8,265,577
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	1,000,000	1,000,000	1,000,000
Unvested restricted stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	0	797,111	0

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details)	12 Months Ended
	Dec. 31, 2017USD ($)Period$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from purchase of common stock	$ 56,000	$ 18,000	$ 964,000
Unrecognized compensation cost, net of estimated forfeitures, related to unvested options and restricted stock	$ 3,300,000
Unrecognized compensation cost, weighted-average recognition period	1 year 4 months 1 day
Stock-based compensation expense	$ 6,972,000	$ 13,714,000	$ 14,700,000
Weighted-average fair value per share of options granted (in dollars per share) | $ / shares	$ 1.17	$ 3.75	$ 8.48
Exercise of stock options (in shares) | shares	0
Aggregate intrinsic value of options exercised		$ 100,000	$ 1,500,000
Related income tax benefits	$ 0	$ 0	$ 0
Stock Incentive Plan, All Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares vested	25.00%
Remaining percentage of shares vested	75.00%
Vesting period, following first year of service, new employees	3 years
Stock options granted, expiration period (no later than)	10 years
2010 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock Issued pursuant to awards granted (up to) (in shares) | shares	9,785,000
Common stock reserved for issuance upon exercise of outstanding awards (in shares) | shares	6,797,090
Common stock that can be issued pursuant to awards granted (up to) (in shares) | shares	2,619,290
2000 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance upon exercise of outstanding awards (in shares) | shares	663,632
2013 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock offering aggregate period	24 months
Number of common stock purchase periods | Period	4
Common stock offering purchase period	6 months
Percentage of common stock purchase price	85.00%
Number of common stock purchased (in shares) | shares	38,648	15,860	124,358
Proceeds from purchase of common stock	$ 100,000	$ 18,000	$ 1,000,000
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock Issued pursuant to awards granted (up to) (in shares) | shares		1,792,250
Stock-based compensation expense	300,000	$ 1,200,000
Fair value measured on the vesting date	$ 300,000	$ 900,000
Weighted average fair value per share of ESPP granted (in dollars per share) | $ / shares	$ 0
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected annual dividend yield	0.00%	0.00%	0.00%
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected annual dividend yield	0.00%	0.00%	0.00%
Weighted average fair value per share of ESPP granted (in dollars per share) | $ / shares	$ 0.99	$ 2.91	$ 4.24

Stock-Based Compensation - Comp

Stock-Based Compensation - Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 6,972	$ 13,714	$ 14,700
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	1,756	6,421	8,474
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 5,216	$ 7,293	$ 6,226

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Restricted Stock Activity (Details) - Restricted stock	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Restricted Stock
Unvested, Beginning of the period (in shares) | shares	797,111
Granted (in shares) | shares	0
Vested (in shares) | shares	(190,989)
Canceled (in shares) | shares	(606,122)
Unvested, End of the period (in shares) | shares	0
Weighted-Average Grant-Date Fair Value
Unvested, Beginning of the period (in dollars per share) | $ / shares	$ 1.43
Granted (in dollars per share) | $ / shares	0
Vested (in dollars per share) | $ / shares	1.54
Canceled (in dollars per share) | $ / shares	1.40
Unvested, End of the period (in dollars per share) | $ / shares	$ 0

Stock-Based Compensation - Fair

Stock-Based Compensation - Fair Value Weighted-Average Assumptions, Stock Options (Details) - Stock Options	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.90%	1.80%	1.50%
Expected annual dividend yield	0.00%	0.00%	0.00%
Expected stock price volatility	90.10%	73.00%	70.80%
Expected term of options	5 years 6 months 30 days	5 years 4 months 30 days	5 years 4 months 24 days

Stock-Based Compensation - Su42

Stock-Based Compensation - Summary of Stock Option Activity (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)$ / sharesshares
Stock Options
Outstanding at beginning of period (in shares) | shares	6,067,945
Granted (in shares) | shares	4,796,500
Exercised (in shares) | shares	0
Forfeited (in shares) | shares	(3,403,723)
Outstanding at end of period (in shares) | shares	7,460,722
Exercisable at end of period (in shares) | shares	3,028,913
Weighted- Average Exercise Price
Outstanding at beginning of period (in dollars per share) | $ / shares	$ 12.06
Granted (in dollars per share) | $ / shares	1.61
Exercised (in dollars per share) | $ / shares	0
Forfeited (in dollars per share) | $ / shares	10.57
Outstanding at end of period (in dollars per share) | $ / shares	6.02
Exercisable at end of period (in dollars per share) | $ / shares	$ 11.53
Weighted-Average Remaining Contractual Life (years)
Outstanding at end of period	7 years 2 months 18 days
Exercisable at end of period	4 years 9 months 18 days
Aggregate Intrinsic Value (in millions)
Outstanding at end of period | $	$ 2
Exercisable at end of period | $	$ 0.2

Stock-Based Compensation - Fa43

Stock-Based Compensation - Fair Value Weighted Average Assumptions, ESPP (Details) - Employee Stock Purchase Plan	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.20%	0.80%	0.40%
Expected annual dividend yield	0.00%	0.00%	0.00%
Expected stock price volatility	102.30%	63.50%	60.30%
Expected term of options	1 year 2 months 30 days	1 year 3 months	1 year 3 months

Cash, Cash Equivalents and Av44

Cash, Cash Equivalents and Available-for-Sale Securities - Summary of Activity (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents, Cost	$ 34,607	$ 74,060
Cash and cash equivalents, Gross Unrealized Gains	0	0
Cash and cash equivalents, Gross Unrealized Losses	0	0
Cash and cash equivalents, Estimated Fair Value	34,607	74,060	$ 188,170	$ 307,405
Total available-for-sale securities, Cost	23,017	18,007
Total available-for-sale securities, Gross Unrealized Gains	0	0
Total available-for-sale securities, Gross Unrealized Losses	(15)	(3)
Total available-for-sale securities, Estimated Fair Value	23,002	18,004
Total cash, cash equivalents and available-for-sale securities, Cost	57,624	92,067
Total cash, cash equivalents and available-for-sale securities, Gross Unrealized Gains	0	0
Total cash, cash equivalents and available-for-sale securities, Gross Unrealized Losses	(15)	(3)
Total cash, cash equivalents and available-for-sale securities, Estimated Fair Value	57,609	92,064
U.S. Treasury securities due in one year or less
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Cost	3,497	6,753
Available-for-sale securities, Gross Unrealized Gains	0	0
Available-for-sale securities, Gross Unrealized Losses	(3)	(1)
Available-for-sale securities, Estimated Fair Value	3,494	6,752
U.S. government-sponsored enterprise obligations due in one year or less
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Cost	19,520	11,254
Available-for-sale securities, Gross Unrealized Gains	0	0
Available-for-sale securities, Gross Unrealized Losses	(12)	(2)
Available-for-sale securities, Estimated Fair Value	$ 19,508	$ 11,252

Cash, Cash Equivalents and Av45

Cash, Cash Equivalents and Available-for-Sale Securities - Additional Information (Details)	12 Months Ended
	Dec. 31, 2017USD ($)SecuritiesFacility	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities debt fair value	$ 23,000,000
Available-for-sale securities realized gains or losses	0	$ 0	$ 0
Other-than-temporary impairments on available-for-sale securities	$ 0	$ 0	$ 0
Less Than Twelve Months
Schedule of Available-for-sale Securities [Line Items]
Number of debt securities held in an unrealized loss position | Securities	13
Foreign Financial Institution and Other Corporate Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities number of financial securities and other corporate debt securities located in foreign countries | Facility	0

Fair Value - Assets Carried at

Fair Value - Assets Carried at Fair Value Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$ 34,607	$ 61,008
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	23,002	31,056
Cash and cash equivalents | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	34,607	61,008
Cash and cash equivalents | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0	13,052
U.S. Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt maturities, next twelve months, fair value	3,494	6,752
U.S. Treasury securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt maturities, next twelve months, fair value	0	0
U.S. Treasury securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt maturities, next twelve months, fair value	3,494	6,752
U.S. government-sponsored enterprise obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt maturities, next twelve months, fair value	19,508	11,252
U.S. government-sponsored enterprise obligations | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt maturities, next twelve months, fair value	0	0
U.S. government-sponsored enterprise obligations | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, debt maturities, next twelve months, fair value	$ 19,508	$ 11,252

Fair Value - Additional Informa

Fair Value - Additional Information (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Transfers of assets between Level 1 and Level 2	$ 0
Transfers of liabilities between Level 1 and Level 2	0
Available-for-sale securities	23,002,000	$ 18,004,000
Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities	$ 0

Prepaid Expenses and Other Cu48

Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Prepaid Expense and Other Assets, Current [Abstract]
Prepaid expenses	$ 563	$ 3,336
Other current assets	214	5,108
Total prepaid expenses and other current assets	$ 777	$ 8,444

Property and Equipment - Summar

Property and Equipment - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 1,830	$ 29,346
Less accumulated depreciation	(1,611)	(5,922)
Property, plant and equipment, net	219	23,424
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,814	4,411
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	0	918
Building and building improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	0	23,586
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 16	$ 431

Property and Equipment - Additi

Property and Equipment - Additional Information (Details) $ in Thousands	Aug. 24, 2017USD ($)	Jun. 19, 2017USD ($)	Mar. 27, 2017USD ($)	Sep. 25, 2014USD ($)ft²	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Apr. 30, 2017USD ($)
Property, Plant and Equipment [Line Items]
Net book value of retired or sold property, plant, and equipment										$ 200	$ 1,300
Proceeds from sale or retirement of fixed assets										900	2,100
Gain from sale or retirement of fixed assets										736	876	$ 0
Property and equipment impairment charges											800
Building and accumulated construction costs											22,000
Financing obligation current and noncurrent											19,600
Other expense						$ 0	$ 0	$ 6,882	$ 0	6,882	0	0
Loss on termination of lease										1,882	$ 0	$ 0
Letters of credit, security deposit				$ 1,000
784 Memorial Drive Premises
Property, Plant and Equipment [Line Items]
Termination payment			$ 5,000							$ 5,000
First installment of the termination payment, paid to the landlord		$ 4,500
Final installment of the termination payment, paid to the landlord	$ 500
Letters of credit, security deposit					$ 500		$ 500
Letter of credit reduction													$ 500
Lease Agreements | 784 Memorial Drive Premises
Property, Plant and Equipment [Line Items]
Lease commencement date				Nov. 1, 2014	Sep. 1, 2017
Lease expiration date				Mar. 31, 2025	Aug. 31, 2019
Area of premises leased under lease agreement | ft²				61,000

Restricted Cash - Additional In

Restricted Cash - Additional Information (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Abstract]
Restricted cash	$ 1.7	$ 1.7

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Accrued restructuring	$ 0	$ 6,920
Accrued compensation and benefits	2,002	5,445
Accrued clinical and development	1,736	7,367
Other	1,398	1,276
Total accrued expenses	$ 5,136	$ 21,008

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	Sep. 25, 2014	Sep. 30, 2017	Nov. 30, 2016USD ($)	Aug. 31, 2019USD ($)	Aug. 31, 2018USD ($)	Dec. 31, 2017USD ($)ft²	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Operating Leased Assets [Line Items]
Termination fee, payment			$ 1,800,000
784 Memorial Drive Premises
Operating Leased Assets [Line Items]
Lease rent expense						$ 400,000	$ 3,200,000	$ 4,600,000
Future minimum payments under the lease						300,000
Future minimum payments, 2018						200,000
Future minimum payments, 2019						$ 100,000
784 Memorial Drive Premises | Lease Agreements
Operating Leased Assets [Line Items]
Area of sublease | ft²						6,091
Lease commencement date	Nov. 1, 2014	Sep. 1, 2017
Lease expiration date	Mar. 31, 2025	Aug. 31, 2019
Scenario, Forecast | 784 Memorial Drive Premises | Lease Agreements
Operating Leased Assets [Line Items]
Lease rent expense					$ 19,796
Monthly base rent of the lease				$ 20,303

Collaborations - Additional Inf

Collaborations - Additional Information (Details)	Mar. 12, 2018USD ($)$ / sharesshares	Oct. 29, 2016USD ($)Product	Jun. 24, 2016	Mar. 31, 2015USD ($)	Sep. 30, 2016	Jun. 30, 2013USD ($)	Mar. 14, 2018USD ($)	Dec. 31, 2016USD ($)shares	Dec. 31, 2017USD ($)shares	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)shares	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2017USD ($)Productshares	Dec. 31, 2016USD ($)shares	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2012USD ($)	Nov. 30, 2015USD ($)	Sep. 06, 2017USD ($)	Jul. 31, 2017USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development									$ 3,552,000	$ 9,338,000	$ 3,901,000	$ 4,039,000	$ 14,662,000	$ 12,814,000	$ 52,947,000	$ 39,188,000	$ 20,830,000	$ 119,611,000	$ 199,109,000
Number of distinct product candidates | Product																	1
Approval and commercialization cost of distinct products, percentage of revenue for qualifying transaction					50.00%
Convertible promissory note, principal								$ 0	6,000,000				0				$ 6,000,000	0
Interest expense									$ 121,000	287,000	300,000	302,000	$ 304,000	305,000	307,000	309,000	1,010,000	1,225,000	1,368,000
Interest paid																	$ 802,000	$ 1,225,000	721,000
Common Stock, shares issued (in shares) | shares								50,374,871	50,761,039				50,374,871				50,761,039	50,374,871
Collaboration revenue									$ 0	$ 6,000,000	$ 0	$ 0	$ 0	0	9,467,000	9,256,000	$ 6,000,000	$ 18,723,000	109,066,000
Gain on AbbVie opt-out													0	$ 0	$ 112,216,000	$ 0	0	112,216,000	0
Takeda Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development																	6,000,000
Convertible promissory note, principal																								$ 6,000,000
Convertible promissory note, interest rate																								8.00%
Interest expense																	200,000
Takeda Agreement | Subsequent Event
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Repayments of debt, cash							$ 4,000,000
Common Stock, shares issued (in shares) | shares	1,134,689
Common stock, share price (in dollars per share) | $ / shares	$ 2.028
Takeda Agreement | Subsequent Event | Common Stock
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Repayments of debt, including interest, noncash							$ 2,300,000
Takeda Agreement | Subsequent Event | Notes Payable
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Extinguishment of debt	$ 6,000,000
Interest paid	300,000
Repayments of debt, cash	4,000,000
Takeda Agreement | Subsequent Event | Notes Payable | Common Stock
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Repayments of debt, including interest, noncash	$ 2,300,000
Verastem Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Prior written notice for termination after the end of the research term		180 days
Number of licensed products | Product		1
Receivable, reimbursement of transition activities and clinical prepaids								$ 4,400,000					$ 4,400,000					4,400,000
Reduction to research and development expense								3,300,000
Reduction to general and administrative expenses								$ 400,000
Payment due upon completion of study																							$ 6,000,000
Collaborative agreement payment due upon approval of drug application									22,000,000								22,000,000
Payment in lieu of cash, percent of common stock shares used in calculation		102.50%
Average share price following milestone achievement, number of days		20 days
Royalty expiration period following first commercial sale of licensed product		10 years
Reduction of royalty percentage on sales of non-patent regulatory exclusivity, percentage		50.00%
Reduction of royalty percentage on third-party payments or patent litigation, percentage		50.00%
Reduction cap of royalty percentage on third-party payments or patent litigation, percentage		50.00%
Verastem Agreement | Mundipharma
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty percentage on sales, reimbursement of research and development, percentage		4.00%
Verastem Agreement | Trailing Mundipharma
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty percentage on sales, reimbursement of research and development upon completion, percentage		1.00%
Verastem Agreement | Trial Closure
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum costs related to shutdown of clinical studies		$ 4,500,000							4,500,000								4,500,000
PellePharm Agreement | Hedgehog Products
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payment amount (up to)						$ 11,000,000
Additional milestone payment amount, upon achievement of certain annual net sales thresholds						$ 37,500,000
PellePharm Agreement | Hedgehog Products | PellePharm
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Right to terminate, prior written notice, period						180 days
AbbVie Opt-Out
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Prior written notice for termination after the end of the research term			90 days
AbbVie Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment received																				$ 275,000,000
Upfront and milestone payments received																						$ 405,000,000
AbbVie Agreement | License
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue																						234,300,000
Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Approval and commercialization cost of distinct products payable (up to)									165,000,000								165,000,000
Maximum | Duvelisib Products
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development																	$ 667,000,000
Current
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Release payment																					$ 15,000,000
Amount paid on release payment during the period																			6,700,000	$ 6,700,000	1,700,000
Research and development																					$ 14,400,000
Prior written notice for termination on the breach of agreement by the other party																	75 days
Prior written notice for termination on nonpayment by the other party																	30 days
Period after notice, to demonstrate failure to be diligent in development and commercializing of licensed product																	3 months
Prior written notice for termination after the end of the research term																	180 days
Current | Amended Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development																			$ 52,500,000
Exercise Fee				$ 52,500,000
Current | Duvelisib Products
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development																	$ 0	9,500,000
Current | AbbVie Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Reduction to research and development expense																		1,000,000
Reduction to general and administrative expenses																		$ 4,400,000
Milestones payments under the terms of the AbbVie agreement																						$ 130,000,000
Current | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development cost of distinct product candidates									$ 5,000,000								$ 5,000,000
Percent of royalty on net sale																	11.00%
Current | Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percent of royalty on net sale																	7.00%

Organizational Restructuring -

Organizational Restructuring - Additional Information (Details)	1 Months Ended	12 Months Ended
	Jun. 30, 2016Patientrestructuring	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Restructuring Cost and Reserve [Line Items]
Research and development, study response rate	46.00%
Research and development, number of research participants with a certain condition | Patient	129
Restructuring and Related Cost, Number of Approved Strategic Restructurings | restructuring	4
Asset impairment charges			$ 800,000
Restructuring and related costs		$ 15,000	21,200,000
Future payments or expected additional costs		0
Contract Termination
Restructuring Cost and Reserve [Line Items]
Restructuring and related costs, write off of prepaid expenses			1,900,000
Restructuring and related costs		$ 15,000
Research and Development Expense
Restructuring Cost and Reserve [Line Items]
Restructuring and related costs			13,600,000
General and Administrative Expense
Restructuring Cost and Reserve [Line Items]
Restructuring and related costs			7,600,000
June 2016 Restructuring
Restructuring Cost and Reserve [Line Items]
Headcount reduction percentage	75.00%
Furniture and fixtures
Restructuring Cost and Reserve [Line Items]
Asset impairment charges			$ 400,000

Organizational Restructuring 56

Organizational Restructuring - Summary of Restructuring Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Restructuring Reserve [Roll Forward]
Amounts accrued at December 31, 2016	$ 6,920
Charges incurred during the year ended December 31, 2017	15	$ 21,200
Amounts paid during the year ended December 31, 2017	6,670
Less non-cash charges during the year ended December 31, 2017	265
Amounts accrued at December 31, 2017	0	6,920
Employee severance, benefits and related costs for work force reduction
Restructuring Reserve [Roll Forward]
Amounts accrued at December 31, 2016	6,892
Charges incurred during the year ended December 31, 2017	0
Amounts paid during the year ended December 31, 2017	6,627
Less non-cash charges during the year ended December 31, 2017	265
Amounts accrued at December 31, 2017	0	6,892
Contract termination, prepaid expense write-offs and other related costs
Restructuring Reserve [Roll Forward]
Amounts accrued at December 31, 2016	28
Charges incurred during the year ended December 31, 2017	15
Amounts paid during the year ended December 31, 2017	43
Less non-cash charges during the year ended December 31, 2017	0
Amounts accrued at December 31, 2017	$ 0	$ 28

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($)	3 Months Ended				12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Provisional income tax expense, Tax Cuts and Jobs Act of 2017					$ 74,500,000
Income taxes benefit (expense)	$ 720,000	$ 0	$ 0	$ 0	720,000	$ 0	$ (335,000)
Tax expense, deferred tax asset, Tax Cuts and Jobs Act of 2017					75,200,000
Tax benefit, Alternative Minimum Tax, Tax Cuts and Jobs Act of 2017					700,000
Increase (decrease) in valuation allowance against deferred tax assets					(57,700,000)	9,900,000	52,000,000
Unrecognized tax benefits	0				0	0
Interest and penalties accrued	0				0	0	0
Interest and penalties expensed					0	$ 0	$ 0
Federal
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Operating loss carry-forward, net	524,100,000				$ 524,100,000
Operating loss carry-forward, expiration date					2,037
Tax credit carry-forward amount	32,500,000				$ 32,500,000
Tax credit carry-forward, expiration date					2,036
State
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Operating loss carry-forward, net	407,300,000				$ 407,300,000
Operating loss carry-forward, expiration date					2,037
Tax credit carry-forward amount	$ 10,200,000				$ 10,200,000
Tax credit carry-forward, expiration date					2,030

Income Taxes - Effective Income

Income Taxes - Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Expected federal tax benefit					$ (14,467)	$ (10,234)	$ (43,534)
Permanent differences					673	1,749	2,263
State taxes, net of the deferred federal benefit					(2,150)	(1,589)	(6,762)
Tax credit carryforwards					0	(37)	(2,735)
Adjustments to deferred tax assets and deferred tax liabilities					5,291	121	(1,267)
Alternative minimum tax					0	0	321
Tax Cut and Jobs Act impact					74,455	0	0
Other					0	79	29
Change in valuation allowance					(64,522)	9,911	52,020
Income tax expense (benefit)	$ (720)	$ 0	$ 0	$ 0	$ (720)	$ 0	$ 335

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets (liabilities):
Net operating loss carryforwards	$ 135,787	$ 178,125
Tax credit carryforwards	40,539	40,051
Intangible assets	22,206	32,199
Accrued expenses	88	822
Stock-based compensation	6,056	11,974
Other, deferred tax assets	391
Other, deferred tax liabilities		(377)
Valuation allowance	(205,067)	(262,794)
Net deferred tax assets	$ 0	$ 0

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - $ / shares	Feb. 24, 2014	Dec. 31, 2017
Equity [Abstract]
Common stock warrants issued (in shares)	1,000,000
Common stock warrants issued, exercise price (in dollars per share)	$ 13.83
Potential percentage of ownership interest (in excess of)	9.985%
Warrants, exercised (in shares)		0

Defined Contribution Benefit 61

Defined Contribution Benefit Plan - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Retirement Benefits [Abstract]
Percentage of employer matching contribution	50.00%	50.00%	50.00%
Participant contributions, employee	6.00%	6.00%	6.00%
Employer matching contribution	$ 0.1	$ 0.8	$ 0.9

Quarterly Financial Informati62

Quarterly Financial Information (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Collaboration revenue	$ 0	$ 6,000	$ 0	$ 0	$ 0	$ 0	$ 9,467	$ 9,256	$ 6,000	$ 18,723	$ 109,066
Operating expenses:
Research and development	3,552	9,338	3,901	4,039	14,662	12,814	52,947	39,188	20,830	119,611	199,109
General and administrative	4,468	4,505	6,205	6,437	8,571	7,120	15,692	10,836	21,615	42,219	37,065
Total operating expenses	8,020	13,843	10,106	10,476	23,233	19,934	68,639	50,024	42,445	161,830	236,174
Gain on AbbVie Opt-Out (note 12)					0	0	112,216	0	0	112,216	0
Income (loss) from operations	(8,020)	(7,843)	(10,106)	(10,476)	(23,233)	(19,934)	53,044	(40,768)	(36,445)	(30,891)	(127,108)
Other income (expenses):
Interest expense	(121)	(287)	(300)	(302)	(304)	(305)	(307)	(309)	(1,010)	(1,225)	(1,368)
Other expense (note 7)	0	0	(6,882)	0					(6,882)	0	0
Investment and other income	124	1,026	334	303	607	741	254	413	1,787	2,015	435
Total other income (expense)	3	739	(6,848)	1	303	436	(53)	104	(6,105)	790	(933)
Loss before income taxes	(8,017)	(7,104)	(16,954)	(10,475)					(42,550)	(30,101)	(128,041)
Income taxes benefit	720	0	0	0					720	0	(335)
Net income (loss)	$ (7,297)	$ (7,104)	$ (16,954)	$ (10,475)	$ (22,930)	$ (19,498)	$ 52,991	$ (40,664)	$ (41,830)	$ (30,101)	$ (128,376)
Basic and diluted loss per common share (in dollars per share)	$ (0.14)	$ (0.14)	$ (0.34)	$ (0.21)					$ (0.83)	$ (0.61)	$ (2.62)
Basic and diluted weighted average number of common shares outstanding (in shares)	50,721,658	50,635,828	50,455,832	50,423,353					50,560,195	49,608,234	49,083,479
Income (loss) per common share:
Basic (in dollars per share)					$ (0.46)	$ (0.39)	$ 1.05	$ (0.82)
Diluted (in dollars per share)					$ (0.46)	$ (0.39)	$ 1.05	$ (0.82)
Weighted average number of common shares outstanding:
Basic (in shares)					50,099,153	49,583,776	49,437,062	49,339,888
Diluted (in shares)					50,099,153	49,583,776	49,439,537	49,339,888

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - USD ($)	Mar. 14, 2018	Mar. 12, 2018	May 31, 2016	Mar. 14, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Subsequent Event [Line Items]
Interest paid					$ 802,000	$ 1,225,000	$ 721,000
Common Stock, shares issued (in shares)					50,761,039	50,374,871
At-The-Market Facility | Cantor Fitzgerald
Subsequent Event [Line Items]
Sales agreement, aggregate offering price (up to)			$ 50,000,000
Sales agreement, commission percentage			3.00%
Subsequent Event | At-The-Market Facility
Subsequent Event [Line Items]
Sale of stock, consideration received on transaction				$ 2,000,000
Subsequent Event | At-The-Market Facility | Cantor Fitzgerald
Subsequent Event [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	950,407
Sale of stock, weighted average price per share (in dollars per share)	$ 2.15			$ 2.15
Subsequent Event | Takeda Agreement
Subsequent Event [Line Items]
Repayments of debt, cash				$ 4,000,000
Common Stock, shares issued (in shares)		1,134,689
Common stock, share price (in dollars per share)		$ 2.028
Subsequent Event | Takeda Agreement | Common Stock
Subsequent Event [Line Items]
Repayments of debt, including interest, noncash				$ 2,300,000
Subsequent Event | Takeda Agreement | Notes Payable
Subsequent Event [Line Items]
Extinguishment of debt		$ 6,000,000
Interest paid		300,000
Repayments of debt, cash		4,000,000
Subsequent Event | Takeda Agreement | Notes Payable | Common Stock
Subsequent Event [Line Items]
Repayments of debt, including interest, noncash		$ 2,300,000