Infinity Pharmaceuticals (INFIQ) 10-K 24 Feb 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2014	Feb. 18, 2015	Jun. 30, 2014
Document Information [Line Items]
Document Type	10-K
Amendment Flag	FALSE
Document Period End Date	31-Dec-14
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Trading Symbol	INFI
Entity Registrant Name	INFINITY PHARMACEUTICALS, INC.
Entity Central Index Key	1113148
Current Fiscal Year End Date	-19
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		48,920,286
Entity Public Float			$605,578,255

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current assets:
Cash and cash equivalents	$307,405	$68,114
Available-for-sale securities	25,321	145,772
Loan commitment asset, net (note 9)	647
Prepaid expenses and other current assets	11,195	11,055
Total current assets	344,568	224,941
Property and equipment, net	18,970	4,010
Long-term available-for-sale securities	519	582
Restricted cash	1,680	1,130
Long-term receivable (note 11)	3,006
Other assets	401	47
Total assets	369,144	230,710
Current liabilities:
Accounts payable	5,947	6,375
Accrued expenses	17,768	9,164
Due to Takeda, current	6,667	6,667
Deferred revenue, current	24,495
Total current liabilities	54,877	22,206
Due to Takeda, less current portion		6,456
Deferred revenue, less current portion	85,510
Deferred rent (note 11)	3,375	458
Construction liability (note 11)	15,456
Other liabilities	454	315
Total liabilities	159,672	29,435
Commitments and contingencies (note 11)
Stockholders' equity:
Preferred Stock, $.001 par value; 1,000,000 shares authorized, no shares issued and outstanding at December 31, 2014 and 2013
Common Stock, $.001 par value; 100,000,000 shares authorized, 48,878,828 and 48,227,838 shares issued and outstanding at December 31, 2014 and December 31, 2013, respectively	49	48
Additional paid-in capital	676,521	650,867
Accumulated deficit	-467,212	-449,796
Accumulated other comprehensive income	114	156
Total stockholders' equity	209,472	201,275
Total liabilities and stockholders' equity	$369,144	$230,710

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Preferred stock, par value	$0.00	$0.00
Preferred stock, shares authorized	1,000,000	1,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common Stock, par value	$0.00	$0.00
Common Stock, shares authorized	100,000,000	100,000,000
Common Stock, shares issued	48,878,828	48,227,838
Common Stock, shares outstanding	48,878,828	48,227,838

Consolidated_Statements_of_Ope

Consolidated Statements of Operations and Comprehensive Loss (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Collaboration revenue	$164,995		$47,114
Operating expenses:
Research and development	143,633	99,760	118,595
General and administrative	29,285	27,916	27,882
Total operating expenses	172,918	127,676	146,477
Gain on termination of Purdue entities alliance			46,555
(Loss) income from operations	-7,923	-127,676	-52,808
Other income (expense):
Interest expense	-9,649		-1,908
Income from Massachusetts tax incentive award			193
Investment and other income	339	896	559
Total other income (expense)	-9,310	896	-1,156
Loss before income taxes	-17,233	-126,780	-53,964
Income tax	-183	0	0
Net (loss) income	-17,416	-126,780	-53,964
Basic and diluted loss per common share	($0.36)	($2.64)	($1.70)
Basic and diluted weighted average number of common shares outstanding	48,561,653	47,936,001	31,711,264
Other comprehensive income (loss):
Net unrealized holding gains (losses) on available-for-sale securities arising during the period	-42	22	112
Comprehensive loss	($17,458)	($126,758)	($53,852)

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating activities
Net loss	($17,416)	($126,780)	($53,964)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	1,773	1,823	1,643
Stock-based compensation, including 401(k) match	12,588	12,155	7,811
Non-cash interest expense on long-term debt due to Purdue entities			1,908
Non-cash interest expense on amount Due to Takeda	211	415
Amortization of loan commitment asset	9,649
Net amortization of premium/discount on available-for-sale securities	1,257	2,201	1,653
Impairment of property and equipment			161
Other, net	83	-2	46
Changes in operating assets and liabilities:
Unbilled accounts receivable			218
Prepaid expenses and other assets	-494	-7,284	-1,037
Accounts payable, accrued expenses and other liabilities	6,815	3,565	-12,395
Due to Takeda	-6,667		12,708
Deferred revenue	110,005		-38,887
Deferred rent	-89
Net cash provided by (used in) operating activities	117,715	-113,907	-80,135
Investing activities
Purchases of property and equipment	-1,362	-1,754	-1,301
Purchases of available-for-sale securities	-21,789	-249,764	-180,498
Proceeds from maturities of available-for-sale securities	141,004	251,093	113,520
Proceeds from sales of available-for-sale securities		1,031	6,281
Net cash provided by (used in) investing activities	117,853	606	-61,998
Financing activities
Proceeds from issuance of common stock related to stock offering, net			244,792
Proceeds from issuance of common stock to Purdue entities			27,500
Proceeds from issuances of common stock related to stock incentive plans	3,881	5,299	21,386
Proceeds from issuances of common stock related to employee stock purchase plan	836	374
Restricted cash	-548
Deferred transaction costs	-446
Net cash provided by financing activities	3,723	5,673	293,678
Net increase (decrease) in cash and cash equivalents	239,291	-107,628	151,545
Cash and cash equivalents at beginning of period	68,114	175,742	24,197
Cash and cash equivalents at end of period	307,405	68,114	175,742
Supplemental schedule of noncash investing and financing activities
Receivable for stock option exercises		152	200
Loan commitment asset	9,850
Facility fee	1,500
Construction liability	15,456
Warrants issued	8,350
Issuance of common stock to extinguish debt from Purdue entities			$51,277

Consolidated_Statements_of_Sto

Consolidated Statements of Stockholders' Equity (USD $)	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
In Thousands, except Share data
Beginning Balance at Dec. 31, 2011	$15,433	$27	$284,436	($269,052)	$22
Beginning Balance (in shares) at Dec. 31, 2011		26,721,739
Exercise of stock options (in shares)		2,632,097
Exercise of stock options	21,586	3	21,583
Exercise of warrants (in shares)		29,958
Exercise of warrants	0	0	0	0	0
Issuance of common stock in connection with public offering (in shares)		12,646,461
Issuance of common stock in connection with public offering	244,792	13	244,779
Issuance of common stock to Purdue entities (in Shares)		5,416,565
Issuance of common stock to Purdue entities	74,435	5	74,430
Stock-based compensation expense	7,117		7,117
401(k) plan match issued in common stock (in shares)		52,437
401(k) plan match issued in common stock	694		694
Unrealized gain on marketable securities	112				112
Net loss	-53,964			-53,964
Ending Balance at Dec. 31, 2012	310,205	48	633,039	-323,016	134
Ending Balance (in shares) at Dec. 31, 2012		47,499,257
Exercise of stock options (in shares)		634,420
Exercise of stock options	5,299		5,299
Exercise of warrants (in shares)		32,248
Exercise of warrants	0	0	0	0	0
Stock-based compensation expense	11,495		11,495
401(k) plan match issued in common stock (in shares)		30,010
401(k) plan match issued in common stock	660		660
Issuance of common stock related to employee stock purchase plan (in shares)		31,903
Issuance of common stock related to employee stock purchase plan	374		374
Unrealized gain on marketable securities	22				22
Net loss	-126,780			-126,780
Ending Balance at Dec. 31, 2013	201,275	48	650,867	-449,796	156
Ending Balance (in shares) at Dec. 31, 2013		48,227,838
Exercise of stock options (in shares)	523,954	523,954
Exercise of stock options	3,881		3,881
Valuation of initial warrants	8,350		8,350
Stock-based compensation expense	11,878		11,878
401(k) plan match issued in common stock (in shares)		50,464
401(k) plan match issued in common stock	710		710
Issuance of common stock related to employee stock purchase plan (in shares)		76,572
Issuance of common stock related to employee stock purchase plan	836	1	835
Unrealized gain on marketable securities	-42				-42
Net loss	-17,416			-17,416
Ending Balance at Dec. 31, 2014	$209,472	$49	$676,521	($467,212)	$114
Ending Balance (in shares) at Dec. 31, 2014		48,878,828

Organization

Organization	12 Months Ended
	Dec. 31, 2014
Organization	1. Organization
	Infinity Pharmaceuticals, Inc. is an innovative biopharmaceutical company dedicated to discovering, developing and delivering best-in-class medicines to patients with difficult-to-treat diseases. 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_Account

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2014
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.
	Reclassifications
	Certain amounts in the prior years’ financial statements have been reclassified to conform with the current-year presentation. These reclassifications have no impact on previously reported net income, net loss or cash flows.
	Cash Equivalents and Available-For-Sale Securities
	Cash equivalents and available-for-sale securities primarily consist of money market funds, U.S. government-sponsored enterprise obligations, corporate obligations and mortgage-backed securities. Corporate obligations include obligations issued by corporations in countries other than the United States, including some obligations that have not been guaranteed by governments and government agencies. 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, 2014 and 2013 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 interest and investment 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
	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. government-sponsored enterprise obligations, investment grade corporate obligations and mortgage-backed securities. 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 discovery and 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 amortization of the deferred revenue associated with the grant of rights and licenses to, and reimbursed research and development services provided to, Mundipharma International Corporation Limited, or Mundipharma, and Purdue Pharmaceutical Products L.P., or Purdue, accounted for all of our revenue during the year ended December 31, 2012. We did not record any revenue in the year ended December 31, 2013 due to the termination of our strategic alliance with Mundipharma and Purdue on July 17, 2012, (see note 12).
	We considered Mundipharma, Purdue and their respective associated entities to be related parties for financial reporting purposes prior to April 2013 because of their equity ownership in us (see note 12).
	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. Assets included in construction in process are not depreciated until placed into service. 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 and capital leases are included in depreciation expense. 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:
	Laboratory equipment		5 years
	Computer equipment and software		3 to 5 years
	Leasehold improvements		Shorter of lease term or useful life of asset
	Furniture and fixtures		7 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. We value the balance of the release payment due to Takeda based on a discounted cash flow model (see note 12).
	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 applicable milestone over the remaining period of performance.
	We will recognize royalty revenue, if any, based upon actual and estimated net sales by the licensee of licensed products in licensed territories, and 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, 2014 and 2013.
	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. 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 (the proceeds of which are then assumed to have been used to repurchase outstanding stock using the treasury stock method) and the exercise of outstanding warrants. 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. Common equivalent shares have not been included in the net loss per share calculations for the periods presented because the effect of including them would have been anti-dilutive. Total potential gross common equivalent shares consisted of the following:
			At December 31,
			2014		2013		2012
	Stock options			6,577,296		6,083,318		5,574,527
	Warrants			1,000,000		—		50,569
	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, 2014, there were no reclassifications out of accumulated other comprehensive income (loss).
	Stock-Based Compensation Expense
	For awards granted to employees and directors, including our 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, and recognize the expense over the requisite service period on a straight-line basis. 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 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 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 we record the reimbursement as revenue. 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, as was the case with our agreement with Intellikine, Inc., or Intellikine, we record the reimbursement or the achievement of the development milestone as research and development expense. In January 2012, Intellikine was acquired by Takeda Pharmaceutical Company Limited, or Takeda, acting through its Millennium business unit. We refer to our phosphoinositide-3-kinase, or PI3K, program licensor as Takeda.

StockBased_Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2014
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 monthly vesting over four years. 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 6,000,000 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, 2014, an aggregate of 4,113,803 shares of our common stock were reserved for issuance upon the exercise of outstanding awards, and up to 2,903,202 shares of common stock may be issued pursuant to awards granted under the 2010 Plan.
	2000 Stock Incentive Plan
	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, 2014, an aggregate of 2,420,345 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.
	2001 Stock Incentive Plan
	In connection with the merger between Discovery Partners International, Inc., or DPI, and Infinity Pharmaceuticals, Inc., or IPI, in 2006, which we refer to as the DPI merger, we assumed awards that were granted under the Infinity Pharmaceuticals, Inc. Pre-Merger Stock Incentive Plan, or the 2001 Plan. The 2001 Plan provided for the grant of incentive stock options, nonstatutory stock options and restricted stock awards. Under the 2001 Plan, stock awards were granted to IPI’s employees, officers, directors and consultants. Incentive stock options were granted at a price not less than fair value of the common stock on the date of grant. The board of directors of IPI determined the vesting of the awards. As of December 31, 2014, an aggregate of 43,148 shares of our common stock were reserved for issuance upon the exercise of outstanding assumed awards. The 2001 Plan was not assumed by us following the DPI merger; therefore, no further grants may be made under the 2001 Plan.
	2013 Employee Stock Purchase Plan
	Our 2013 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. During 2014, 76,572 shares of common stock were purchased for total proceeds of $0.8 million. During 2013, 31,903 shares of common stock were purchased for total proceeds of $0.4 million.
	Compensation Expense
	Total stock-based compensation expense, related to all equity awards, comprised the following:
			Year Ended
			December 31,
			2014			2013			2012
			(in thousands)
	Research and development		$	7,502		$	6,213		$	3,177
	General and administrative			5,086			5,942			4,634
	As of December 31, 2014, we had approximately $17.1 million of total unrecognized compensation cost, net of estimated forfeitures, related to unvested options and awards under our ESPP, which are expected to be recognized over a weighted-average period of 2.2 years.
	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:
			Year Ended
			December 31,
			2014			2013			2012
	Risk-free interest rate			1.7	%		1.1	%		1.1	%
	Expected annual dividend yield			—			—			—
	Expected stock price volatility			70.9	%		64.6	%		63.3	%
	Expected term of options			5.0 years			5.4 years			6.1 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. We used historical data and expectations for the future to estimate employee exercise and post-vest termination behavior.
	We stratify employees into two groups to evaluate exercise and post-vesting termination behavior. We estimate forfeitures based upon historical data, adjusted for known trends, and will adjust the estimate of forfeitures if actual forfeitures differ or are expected to differ from such estimates. Subsequent changes in estimated forfeitures are recognized through a cumulative adjustment in the period of change and will also impact the amount of stock-based compensation expense in future periods. As of December 31, 2014, 2013 and 2012, the weighted-average forfeiture rate was estimated to be 14%, 13% and 12%, respectively.
	All options granted to employees during the years ended December 31, 2014, 2013 and 2012 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, 2014 is as follows:
			Stock Options			Weighted-Average			Weighted-Average			Aggregate
						Exercise Price			Remaining  Contractual			Intrinsic Value
									Life			(in millions)
									(years)
	Outstanding at January 1, 2014			6,083,318		$	14.04
	Granted			1,576,734			12.6
	Exercised			(523,954	)		7.41
	Forfeited			(558,802	)		19.53
	Outstanding at December 31, 2014			6,577,296		$	13.76			6.3		$	37.5
	Vested or expected to vest at December 31, 2014			6,274,310		$	13.59			6.1		$	36.5
	Exercisable at December 31, 2014			4,704,549		$	12.08			5.3		$	31.1
	The weighted-average fair value per share of options granted during the years ended December 31, 2014, 2013 and 2012 was $7.45, $18.07 and $6.00, respectively.
	The aggregate intrinsic value of options outstanding at December 31, 2014 was calculated based on the positive difference between the closing fair market value of our common stock on December 31, 2014 and the exercise price of the underlying options. The aggregate intrinsic value of options exercised during the years ended December 31, 2014, 2013 and 2012 was $4.0 million, $16.0 million and $34.1 million, respectively. The total cash received from employees and non-employees as a result of stock option exercises during the year ended December 31, 2014 was $3.9 million.
	No related income tax benefits were recorded during the years ended December 31, 2014, 2013 or 2012.
	We settle employee stock option exercises with newly issued shares of our common stock.
	During the year ended December 31, 2014, two members of our board of directors retired, and we extended these directors’ rights to exercise their vested stock options for an additional six-month period. In addition, one employee whose employment terminated received an accelerated vesting of his unvested options. In connection with these modifications, we recognized an additional $0.4 million of stock-based compensation expense during the year ended December 31, 2014.
	During the year ended December 31, 2012, two members of our board of directors retired, and we extended these directors’ rights to exercise their vested stock options from 90 days following their retirement to two years following their retirement. In connection with these extensions, we recognized an additional $0.3 million of stock-based compensation expense during the year ended December 31, 2012 with respect to the modification of these awards. In addition, during the year ended December 31, 2012, the chair of our board of directors resigned and entered into a three-year substantive consulting agreement to act as a strategic advisor. As a result of this transition, we recognized $1.2 million of non-employee stock-based compensation expense in general and administrative expenses during the year ended December 31, 2012 with respect to the options that continue to vest. The fair value of the unvested options will be remeasured at each reporting date until the options have fully vested. We recognized $0.7 million of non-employee stock-based compensation expense in general and administrative expenses during the year ended December 31, 2013 with respect to the remeasurement and continued vesting of these options. The amount recognized related to the remeasurement and continued vesting of these options during the year ended December 31, 2014 was not material.
	Employee Stock Purchase Plan
	The weighted-average fair value of each purchase right granted during the year ended December 31, 2014 and 2013 was $5.66 and $8.68, respectively. For the years ended December 31, 2014 and 2013, the fair values were estimated using the Black-Scholes valuation model using the following weighted-average assumptions:
			December 31, 2014			December 31, 2013
	Risk-free interest rate			0.3	%		0.3	%
	Expected annual dividend yield			—			—
	Expected stock price volatility			66.7	%		91.5	%
	Expected term of options			1.25 years			1.25 years

Cash_Cash_Equivalents_and_Avai

Cash, Cash Equivalents and Available-for-Sale Securities	12 Months Ended
	Dec. 31, 2014
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, 2014
		Cost		Gross		Gross			Estimated
				Unrealized		Unrealized			Fair Value
				Gains		Losses
		(in thousands)
	Cash and cash equivalents due in 90 days or less	$	307,405	$	—	$	—		$	307,405
	Available-for-sale securities:
	Corporate obligations due in one year or less		21,324		6		(1	)		21,329
	Mortgage-backed securities due after ten years		412		107		—			519
	U.S. government-sponsored enterprise obligations due in one year or less		3,990		2		—			3,992
	Total available-for-sale securities		25,726		115		(1	)		25,840
	Total cash, cash equivalents and available-for-sale securities	$	333,131	$	115	$	(1	)	$	333,245
		December 31, 2013
		Cost		Gross		Gross			Estimated
				Unrealized		Unrealized			Fair Value
				Gains		Losses
		(in thousands)
	Cash and cash equivalents due in 90 days or less	$	68,114	$	—	$	—		$	68,114
	Available-for-sale securities:
	Corporate obligations due in one year or less		103,889		18		(16	)		103,891
	Corporate obligations due in one to five years		13,513		32		—			13,545
	Mortgage-backed securities due after ten years		478		104		—			582
	U.S. government-sponsored enterprise obligations due in one year or less		24,144		13		—			24,157
	U.S. government-sponsored enterprise obligations due in one to five years		4,174		5		—			4,179
	Total available-for-sale securities		146,198		172		(16	)		146,354
	Total cash, cash equivalents and available-for-sale securities	$	214,312	$	172	$	(16	)	$	214,468
	We held four debt securities at December 31, 2014 that had been in an unrealized loss position for less than twelve months. The fair value of these securities was $15.0 million. We evaluated our securities for other-than-temporary impairments based on quantitative and qualitative factors. We considered the decline in market value for these four 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, 2014.
	As of December 31, 2014, we held securities of six financial institutions and other corporate debt securities located in Canada, Sweden, France, the United Kingdom and Japan with a fair value of $50.7 million. These securities are short term in nature and are all scheduled to mature within twelve months. There were no material unrealized losses incurred by these securities.
	We had no material realized gains or losses on our available-for-sale securities for the years ended December 31, 2014, 2013 and 2012. There were no other-than-temporary impairments recognized for the years ended December 31, 2014, 2013 and 2012.

Fair_Value

Fair Value	12 Months Ended
	Dec. 31, 2014
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, 2014 and 2013.
	The following table provides the assets carried at fair value measured on a recurring basis as of December 31, 2014:
			Level 1		Level 2
			(in thousands)
	Assets:
	Cash and cash equivalents		$	256,559	$	50,846
	Corporate obligations (including commercial paper)			—		21,329
	Mortgage-backed securities			—		519
	U.S. government-sponsored enterprise obligations			—		3,992
	Total		$	256,559	$	76,686
	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:
		•		Corporate Obligations:
		•		Commercial paper: calculations by custodian based on the three month Treasury bill published on last business day of the month.
		•		Other: benchmark yields, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers and reference data.
		•		Mortgage-backed securities: benchmark yields, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers and reference data, new issue data, monthly payment information and collateral performance.
		•		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.
	The amount due to Takeda is recorded at its carrying value at December 31, 2014. The fair value of the amount due to Takeda, a Level 2 measurement, was approximately $6.7 million as of December 31, 2014 and was determined using a discounted cash flow model and based on an interest rate we would be charged for a similar loan as of December 31, 2014 (see note 12).
	The carrying amounts reflected in the consolidated balance sheets for unbilled accounts receivable, 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 the valuation methods during the year ended December 31, 2014. 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, 2014. We had no available-for-sale securities that were classified as Level 3 at any point during the years ended December 31, 2014 or 2013.

Prepaid_expenses_and_other_cur

Prepaid expenses and other current assets	12 Months Ended
	Dec. 31, 2014
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,
		2014		2013
		(in thousands)
	Prepaid comparator drug	$	5,085	$	6,673
	Prepaid expenses		4,124		2,044
	Other current assets		1,986		2,338
	Total prepaid expenses and other current assets	$	11,195	$	11,055

Property_and_Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2014
Property and Equipment	7. Property and Equipment
	Property and equipment consist of the following:
		December 31,
		2014			2013
		(in thousands)
	Laboratory equipment	$	12,615		$	14,958
	Computer hardware and software		5,550			6,488
	Office equipment and furniture and fixtures		720			872
	Construction in process		16,004			—
	Leasehold improvements		5,041			4,982
			39,930			27,300
	Less accumulated depreciation		(20,960	)		(23,290	)
		$	18,970		$	4,010
	During the year ended December 31, 2014, we entered into a lease agreement for the lease of office space at 784 Memorial Drive, Cambridge, Massachusetts. Upon lease commencement, building construction was initiated and we are involved in the construction project. We are deemed for accounting purposes to be the owner of the building during the construction period. As of December 31, 2014, we recognized the building as construction in process for $14.7 million on our consolidated balance sheet (see note 11).
	During the year ended December 31, 2013, we capitalized approximately $0.4 million of costs associated with internally developed software. Depreciation expense associated with this software was $0.1 million and $49 thousand during 2014 and 2013, respectively.

Restricted_Cash

Restricted Cash	12 Months Ended
	Dec. 31, 2014
Restricted Cash	8. Restricted Cash
	We held $1.7 million and $1.1 million in restricted cash as of December 31, 2014 and December 31, 2013, respectively. The balances are 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.

Debt_Facility_Agreement

Debt Facility Agreement	12 Months Ended
	Dec. 31, 2014
Debt Facility Agreement	9. Debt Facility Agreement
	On February 24, 2014, we entered into a facility agreement with affiliates of Deerfield Management Company, L.P., or Deerfield, pursuant to which, Deerfield agreed to loan us up to $100 million, subject to the terms and conditions set forth in the facility agreement. On September 22, 2014, we amended the facility agreement with Deerfield such that the maximum principal amount that we may draw down is reduced to $50 million. We refer to the facility agreement with Deerfield, as amended, as the Facility Agreement. Under the terms of the Facility Agreement, we had the right to draw down on the Facility Agreement in $25 million minimum disbursements, which we refer to as the Loan Commitment, at any time on 22 business days’ prior notice until February 27, 2015, which we refer to as the Draw Period. The Draw Period has expired without us having drawn down on the Facility Agreement.
	On February 27, 2015, or upon the earlier termination of the facility, we are required to pay a fee equal to 3% of the difference between the $50 million commitment and the aggregate amount of any disbursements under the Facility Agreement made prior to such date, which we refer to as the Facility Fee. As no disbursements have been made under the Facility Agreement and the Draw Period has expired, we have determined it probable that we will be required to pay a Facility Fee amount of $1.5 million on February 27, 2015. We have recorded the full $1.5 million Facility Fee on the December 31, 2014 consolidated balance sheet as a component of both the loan commitment asset and accrued expenses line items. The loan commitment asset is being amortized to interest expense in the consolidated statements of operations and comprehensive loss on a straight line basis over the Draw Period.
	In connection with the execution of the 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 it exceeding 9.985% of the total number of shares of common stock then issued and outstanding.
	Our total cost of securing the Loan Commitment was $11.8 million and is comprised of $8.4 million representing the fair value of the 1,000,000 warrants issued on February 24, 2014, discussed below; $3 million representing the Facility Fee; and $0.4 million of transaction costs. As a result of the amendment of the Facility Agreement, we reduced the Facility Fee by 50%, or $1.5 million and recorded a corresponding decrease in the loan commitment asset. In addition, since our borrowing capacity was reduced by 50%, the remaining loan commitment asset outstanding as of September 22, 2014 was also reduced by 50% resulting in an additional expense of $1.8 million during the year ended December 31, 2014. The total fair value is considered a Loan Commitment Asset which has been classified as a current asset on the December 31, 2014 consolidated balance sheets. This amount is considered a fee to secure the Loan Commitment and is being amortized to interest expense in the year ended December 31, 2014 consolidated statements of operations and comprehensive loss on a straight line basis over the Draw Period. We recorded $9.6 million of interest expense associated with the amortization and write-off of the loan commitment asset pursuant to the modification of the facility for the year ended December 31, 2014.

Accrued_Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2014
Accrued Expenses	10. Accrued Expenses
	Accrued expenses consisted of the following:
		December 31,
		2014		2013
		(in thousands)
	Accrued compensation and benefits	$	7,353	$	1,839
	Accrued drug manufacturing costs		1,280		991
	Accrued clinical studies		5,134		4,009
	Accrued preclinical studies		543		303
	Facility fee		1,500		—
	Other		1,958		2,022
	Total accrued expenses	$	17,768	$	9,164

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies	11. Commitments and Contingencies
	We lease our office and laboratory space under two separate lease agreements with BHX, LLC, as trustee of 784 Realty Trust, and ARE-770/784/790 Memorial Drive, LLC.
	BHX, LLC, as Trustee of 784 Realty Trust
	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 expires on March 31, 2025, the Expiration Date. Pursuant to the Lease, on the Commencement Date we agreed to lease 61,000 square feet of the leased premises, which represents the entire building, the Leased Premises.
	From the Commencement Date until April 1, 2015, the total base rent of the Lease will be zero per month. From April 1, 2015 through March 31, 2020, the total base rent of the Lease will be $170,292 per month. From April 1, 2020 until the Expiration Date, the total base rent of the Lease will be $190,625 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. Pursuant to the terms of the Lease, we provided a security deposit in the form of a letter of credit in the initial amount of $1.0 million, which may be reduced by up to $750,000 over time in accordance with the terms of the Lease. The Landlord has agreed to pay up to $5,856,100 for certain updates and repairs to be made to the Leased Premises. We are responsible for the construction and bear the risk of cost over-runs.
	We have two consecutive rights to extend the term of the Lease for five years under each extension, provided that we provide notice to the Landlord no earlier than 18 months or later than 12 months prior to expiration of the Lease. The base rent for each extension term shall be equal to 95% of the then fair market base rent per square foot for the premises.
	The Lease contains customary provisions allowing the Landlord to terminate the lease if we fail to remedy a default of any of our obligations under the Lease within specified time periods or upon our bankruptcy or insolvency.
	Upon lease commencement on November 1, 2014, building construction was initiated to suit our future needs. We are involved in the construction project, including having responsibility to pay for a portion of the structural elements of the building and bear the risk of cost over-runs. Therefore, we are deemed for accounting purposes to be the owner of the building during the construction period. Accordingly, we determined the fair value of the building as of November 1, 2014 through an independent appraisal and recorded the building as an asset on our consolidated balance sheet, together with a corresponding construction financing obligation, in November 2014 when the lease and construction commenced. On our consolidated balance sheet, we record project construction costs as an asset during the construction period and reflect an increase in the construction financing obligation for the amount of Landlord incentives received. When the construction is substantially complete and the Leased Premises is available for occupancy, the construction-in-progress will be placed in service and the construction liability will be reclassified to a financing obligation. We will commence depreciation on the building and accumulated construction costs over the term of the lease using a residual value equal to the financing obligation at the end of the lease term as such transaction is not expected to qualify for sale-leaseback accounting. Interest expense will be recorded on a monthly basis using an estimated incremental borrowing rate and will commence at the time the building is placed into service. The construction financing obligation will be reduced on a monthly basis commencing in April 2015 by that portion of the lease payment allocated to construction financing obligation principal.
	At December 31, 2014, the accompanying consolidated balance sheet reflects the building and accumulated construction costs of approximately $16.0 million and a construction liability of approximately $15.5 million.
	We divide our future lease payments into a portion that is allocated to the financing obligation and a portion that is allocated to the land on which the building is located. The portion of the lease obligation allocated to the land is treated for accounting purposes as an operating lease commencing in November 2014 and recorded on a straight-line basis over the initial lease term. Rent expense pertaining to the land was approximately $68,000 for the year ended December 31, 2014.
	We will make our first monthly lease payment under the Lease on April 1, 2015, which provides us a rent free period of five months. Upon signing the lease agreement, we paid the first month’s rent in the amount of $170,292, which was recorded as a prepaid expense on the accompanying consolidated balance sheets. In addition, we provided a letter of credit in the amount of $1.0 million to the Landlord as security for the lease. The letter of credit plus the associated bank fee of $30,000 has been recorded in our accompanying consolidated balance sheets as restricted cash.
	ARE-770/784/790 Memorial Drive, LLC
	On November 6, 2014, we entered into a Seventh Amendment to Lease, the Lease Amendment, by and between us and ARE-770/784/790 Memorial Drive, LLC, the landlord, or ARE, which amends the lease agreement originally dated July 2, 2002, as amended to date, or the Original Lease. We shall refer to the Original Lease together with the Lease Amendment as the Memorial Drive Lease. We shall refer to the area rented under the Memorial Drive Lease as the Premises.
	Under the Lease Amendment: (i) the Premises consist of 54,861 square feet, of which 51,000 square feet are located at 780 Memorial Drive, or the 780 Premises, and the remaining 3,861 square feet are located at 790 Memorial Drive, or the 790 Premises; effective February 1, 2016 we will surrender 13,159 square feet of the previously leased 17,020 square feet at the 790 Premises; (ii) we have extended the base term of the Memorial Drive Lease through March 31, 2025; and (iii) we have two separate five-year options to extend the term of the Memorial Drive Lease to 2035 on the same terms and conditions (other than with respect to base rent or any work letter). The Memorial Drive Lease provides that we shall continue to pay the base rent as provided in the Original Lease until January 31, 2016. The base rent shall then increase to $69.00 per square foot of the Premises on February 1, 2016 and again to $70.00 per square foot of the Premises on February 1, 2018. The Memorial Drive Lease provides that no base rent for the Premises shall be due (i) for the period commencing on February 1, 2015 through July 31, 2015, (ii) for the period commencing on February 1, 2016 through February 29, 2016, (iii) for the period commencing on February 1, 2017 through February 28, 2017, and (iv) for the period commencing on February 1, 2018 through February 28, 2018. We also received allowances of $3.0 million for the design and construction of tenant improvements. The total of these allowances of $3.0 million has been reflected on our Consolidated Balance Sheet at December 31, 2014 as a long-term receivable, with a corresponding amount included in deferred rent liability. The deferred rent is being amortized to rent expense over the term of the lease.
	We have determined that the proposed improvements on the 780 Premises generally consists of normal tenant improvements and that we will not be deemed for accounting purposes to be the owner of the building during the construction period.
	Future minimum payments, excluding operating costs and taxes, under the two lease agreements described above are as follows:
		784 Facility Lease		780/790 Facility Lease
		(in thousands)
	Years Ending December 31:
	2015	$	1,362	$	2,792
	2016		2,044		3,556
	2017		2,044		3,470
	2018		2,044		3,516
	2019		2,044		3,840
	2020 and beyond		11,947		20,161
	Total minimum lease payments	$	21,485	$	37,335
	Rent expense of $4.7 million, $4.7 million and $4.8 million, before considering sublease income, was incurred during the years ended December 31, 2014, 2013 and 2012, respectively. Deferred rent is being amortized to rent expense over the life of the lease. During the years ended December 31, 2014, 2013 and 2012, we subleased a portion of our facility space for total sublease income of $0.2 million, $0.2 million and $0.7 million, respectively. We record sublease payments as an offset to rental expense in our consolidated statements of operations and comprehensive loss. The sublease expires January 2016. Future minimum sublease income under the existing sublease is expected to be $0.2 million for the year ended December 31, 2015.

Collaborations

Collaborations	12 Months Ended
	Dec. 31, 2014
Collaborations	12. Collaborations
	AbbVie
	On September 2, 2014, we entered into a collaboration and license agreement with AbbVie Inc., or AbbVie, which we refer to as the AbbVie Agreement. Under the AbbVie Agreement, we will collaborate with AbbVie to develop and commercialize products containing duvelisib, which we refer to as Duvelisib Products, in oncology indications. Under the terms of the AbbVie Agreement, we have granted to AbbVie licenses under applicable patents, patent applications, know-how and trademarks to develop, commercialize and manufacture Duvelisib Products in oncology indications. These licenses are generally co-exclusive with rights we retain, except that we have granted AbbVie exclusive licenses to commercialize Duvelisib Products outside the United States. We and AbbVie retain the rights to perform our respective obligations and exercise our respective rights under the AbbVie Agreement, and we and AbbVie may each grant sublicenses to affiliates or third parties.
	Under the AbbVie Agreement, we and AbbVie have created a governance structure, including committees and working groups to manage the development, manufacturing and commercialization responsibilities for Duvelisib Products. Generally, we and AbbVie must mutually agree on decisions, although in specified circumstances either we or AbbVie would be able to break a deadlock.
	We and AbbVie share oversight of development and have each agreed to use diligent efforts, as defined in the AbbVie Agreement, to carry out our development activities under an agreed upon development plan. We have primary responsibility for the conduct of development of Duvelisib Products, unless otherwise agreed, and AbbVie has responsibility for the conduct of certain contemplated combination clinical studies, which we refer to as the AbbVie Studies. We have the responsibility to manufacture Duvelisib Products until we transition manufacturing responsibility to AbbVie, which we expect to occur as promptly as practicable while ensuring continuity of supply. Excluding the AbbVie Studies, we are responsible for all costs to develop and manufacture Duvelisib Products up to a maximum amount of $667 million after which we will share Duvelisib Product development and manufacturing costs equally with AbbVie. The development and manufacturing costs for the AbbVie Studies will be shared equally.
	We and AbbVie share operational responsibility and decision making authority for commercialization of Duvelisib Products in the United States. Specifically, we have the primary responsibility for advertising, distribution, and booking sales, and we share certain other commercialization functions with AbbVie. Assuming regulatory approval, we and AbbVie are obligated to each provide half of the sales representative effort to promote Duvelisib Products in the United States. Outside the United States, AbbVie has, with limited exceptions, operational responsibility and decision making authority to commercialize Duvelisib Products. We and AbbVie will share the cost of manufacturing and supply for commercialization of Duvelisib Products in the United States and AbbVie will bear the cost of manufacturing and supply for commercialization of Duvelisib Products outside the United States. Prior to commercialization and regulatory approval, we will recognize these costs as a component of research and development and general and administrative expenses. Subsequent to regulatory approval and commercial launch, the cost of manufacturing will be recorded as cost of goods sold. We recognize these costs as a component of research and development and general and administrative expenses. During the year ended December 31, 2014, we recognized a credit of $0.1 million in general and administrative expenses related to these costs.
	AbbVie has paid us a non-refundable $275 million upfront payment and has agreed to pay us up to $530 million in potential future milestone payments comprised of $130 million associated with the completion of enrollment of either DYNAMO or DUO, which we expect to occur in 2015, up to $275 million associated with the achievement of specified regulatory filing and approval milestones, and up to $125 million associated with the achievement of specified commercialization milestones. Under the terms of the AbbVie Agreement, we and AbbVie will equally share commercial profits or losses of Duvelisib Products in the United States, including sharing equally the existing royalty obligations to Mundipharma International Corporation Limited, or Mundipharma, and Purdue Pharmaceutical Products L.P., or Purdue, for sales of Duvelisib Products in the United States, as well as sharing equally the existing U.S. milestone payment obligations to Takeda. Additionally, AbbVie has agreed to pay us tiered royalties on net sales of Duvelisib Products outside the United States ranging from 23.5% to 30.5%, depending on annual net sales of Duvelisib Products by AbbVie, its affiliates and its sublicensees. We are responsible for the existing royalty obligations to Mundipharma and Purdue outside the United States and to Takeda worldwide, and AbbVie has agreed to reimburse us for our existing Duvelisib Product milestone payment obligations to Takeda outside the United States. The tiered royalty from AbbVie is subject to a reduction of 4% at each tier if our royalties to Mundipharma and Purdue are reduced according to the terms of our respective agreements with them. This tiered royalty can further be reduced based on specified factors, including patent expiry, generic entry, and royalties paid to third parties with blocking intellectual property. These royalties are payable on a product-by-product and country-by-country basis until AbbVie ceases selling the product in the country.
	We have evaluated the deliverables within the AbbVie Agreement to determine whether or not they provide value on a standalone basis. Based on our evaluation, we have determined that there are three deliverables: the license, the development services and the committee services, and each provides value on a stand-alone basis and represents a separate unit of accounting. We determined the best estimate of selling price for each unit of accounting using a discounted cash-flow model. The valuation for each deliverable involves significant estimates and assumptions, including but not limited to, expected market opportunity, assumed royalty rates, pricing objectives, clinical trial timelines, likelihood of success and projected costs. The resulting estimate of selling prices for the license and development services consider the benefits that have been retained by us.
	Of the $275 million upfront payment received during the year ended December 31, 2014, $159.1 million was allocated to the license, $115.6 million to the development services and $0.3 million to committee services based on the allocation of best estimate of selling price on a relative basis. We determined the best estimate of selling prices for the license unit of accounting based on estimates and assumptions resulting in an expected future cash flow which was discounted based on estimated weighted average cost of capital of 11.5%. We determined the best estimate of selling prices for development and committee services based on the nature of the services to be performed and estimates of the associated efforts and third-party rates for similar services using a discount rate of 8% for development services and 11.5% for committee services. We recognized license revenue upon execution of the arrangement. Revenue related to development services and committee services are being recognized using the proportionate performance method as services are provided over the estimated service period of approximately five years. During the year ended December 31, 2014, we recognized $159.1 million of revenue related to the license and $5.9 million of revenue related to development and committee services. We have recorded the remaining amount of $110 million related to development and committee services as deferred revenue as of December 31, 2014.
	The development, regulatory and commercialization milestones represent non-fundable amounts that would be paid by AbbVie to us if certain milestones are achieved in the future. We have elected to apply the milestones method of revenue recognition to these milestones. We have determined that all milestones, except for the first milestone, if achieved, are substantive as they relate solely to past performance, are commensurate with estimated enhancement of value associated with the achievement of each milestone as a result of our performance, which are reasonable relative to other deliverables and terms of the arrangement, and are unrelated to the delivery of any further elements under the arrangement. The clinical development milestone, which we have determined not to be substantive based on risk and effort involved, will be recognized using the same method as the upfront payment when achieved.
	Subject to limited exceptions, we have agreed that we and our affiliates will not commercialize, or assist others in commercializing, in oncology indications any product that is a PI3K delta, gamma inhibitor that meets certain agreed-to criteria, other than Duvelisib Products, and AbbVie has agreed to similar restrictions. Registration-directed clinical trials and commercialization of Duvelisib Products for uses outside of oncology indications would require our and AbbVie’s mutual consent.
	The AbbVie Agreement will remain in effect until all development, manufacturing and commercialization of Duvelisib Products cease, unless terminated earlier. Either we or AbbVie may terminate the AbbVie Agreement if the other party is subject to certain insolvency proceedings or if the other party materially breaches the AbbVie Agreement and the breach remains uncured for a specified period, which may be extended in certain circumstances. However, we may terminate the AbbVie Agreement only on a country by country basis in the event AbbVie is not using diligent efforts to obtain regulatory approval or to commercialize Duvelisib Products in a country outside the United States. AbbVie may also terminate the AbbVie Agreement for convenience after a specified notice period. In the event there is a material uncured breach by either us or AbbVie of development or commercialization obligations, the non-breaching party may also have the right to assume and conduct such applicable development or commercialization obligations. If AbbVie or any of its affiliates or sublicensees challenges the patents we have licensed to AbbVie, we can terminate the AbbVie Agreement if the challenge is not withdrawn after a specified notice period.
	If the AbbVie Agreement is terminated, we would receive all rights to the regulatory filings related to duvelisib upon our request, our license to AbbVie would terminate, and AbbVie would grant us a perpetual, irrevocable license to develop, manufacture and commercialize products containing duvelisib, excluding any compound which is covered by patent rights controlled by AbbVie or its affiliates. This license would be royalty free, unless the AbbVie Agreement is terminated for material breach, in which case, depending on the breaching party and the timing of the material breach, a royalty rate may be payable by us ranging from a low single-digit percentage to a low double-digit percentage of net sales, and, in some cases, subject to a payment cap.
	If the AbbVie Agreement is terminated, there are certain wind-down obligations to ensure a smooth transition of the responsibilities of the parties including, unless the AbbVie Agreement is terminated by AbbVie for our material breach, the continued conduct of certain development and commercialization activities by AbbVie for a limited transition period and the continued funding by AbbVie of its half of the cost of the AbbVie Studies ongoing at the time of termination.
	Takeda
	In July 2010, we entered into a development and license agreement with Intellikine, under which we obtained rights to discover, develop and commercialize pharmaceutical products targeting the delta and/or gamma isoforms of PI3K, including duvelisib, and we paid Intellikine a $13.5 million up-front license fee. In January 2012, Intellikine was acquired by Takeda, acting through its Millennium business unit. We refer to our PI3K program licensor as Takeda. In December 2012, we amended and restated our development and license agreement with Takeda.
	Under the terms of the amended and restated agreement, we retained worldwide development rights and, in exchange for an agreement to pay Takeda $15 million in installments, we regained commercialization rights for products arising from the agreement for all therapeutic indications and are solely responsible for research conducted under the agreement. During the year ended December 31, 2012, we paid $1.7 million of the $15 million, and we recorded the $15 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. The remaining amount is due in January 2015, which we recorded as short-term liability due to Takeda on our consolidated balance sheet.
	In addition to developing duvelisib, we are seeking to identify additional novel inhibitors of PI3K-delta and/or PI3K-gamma for future development. We are obligated to pay to Takeda up to $5 million in remaining success-based milestone payments for the development of a second product candidate and up to $450 million in success-based milestones for the approval and commercialization of two distinct products. In February 2014, we paid Takeda a $10 million milestone payment in connection with the initiation of our Phase 3 study of duvelisib in patients with relapsed or refractory chronic lymphocytic leukemia, or CLL. We recognized the $10 million payment as research and development expense during the year ended December 31, 2014. In addition, we are obligated to pay Takeda tiered royalties on worldwide net sales ranging from 7% to 11% upon successful commercialization of products described in the agreement. Such royalties are payable until the later to occur of the expiration of specified patent rights and 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.
	The amended and restated 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. Either party may terminate the 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 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 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 agreement also provides for customary reciprocal indemnification obligations of the parties.
	On July 29, 2014, we entered into an amendment to amended and restated development and license our agreement with Takeda. Under the terms of the amendment, we paid to Takeda a one-time upfront payment of $5 million in exchange for the option to terminate our royalty obligations to Takeda under the amended and restated development and license agreement solely with respect to worldwide net sales in oncology indications of products containing or comprised of duvelisib. The option may be exercised by payment to Takeda of a fee of $52.5 million on or before March 31, 2015. If the option is not exercised, our royalty obligations to Takeda will remain unchanged. We recognized the $5 million upfront payment as research and development expense during the year ended December 31, 2014 as there is no alternative future use beyond the existing research and development activities.
	FAAH Program License
	In August 2014, we licensed rights to our fatty acid amide hydrolase, or FAAH program, to FAAH Pharma Inc., or FAAH Pharma, a start-up company pursuing the clinical development of IPI-940 to investigate its potential to treat neuropathic pain. We received a 23% ownership in FAAH Pharma in exchange for the license. FAAH Pharma receives funding from TVM Life Science Ventures VII, L.P., or TVM, under potential milestone payments. We have elected to use the carryover basis of measurement and no gain or loss is recognized related to this transaction.
	Mundipharma and Purdue
	Strategic Alliance Termination Agreements
	On July 17, 2012, we terminated our strategic alliance with Mundipharma International Corporation Limited, or Mundipharma, and Purdue Pharmaceutical Products L.P., or Purdue, and we entered into termination and revised relationship agreements with each of those entities, which we refer to as the 2012 Termination Agreements. We considered Mundipharma, Purdue and their respective associated entities to be related parties for financial reporting purposes prior to April 2013 because of their equity ownership in us. The strategic alliance was previously governed by strategic alliance agreements that we entered into with each of Mundipharma and Purdue in November 2008. The strategic alliance agreement with Purdue was focused on the development and commercialization in the United States of products targeting FAAH. The strategic alliance agreement with Mundipharma was focused on the development and commercialization outside of the United States of all products and product candidates that inhibit or target the Hedgehog pathway, FAAH, PI3K, and product candidates arising out of our early discovery projects in all disease fields.
	Under the terms of the 2012 termination agreements:
		•	All intellectual property rights that we had previously licensed to Mundipharma and Purdue to develop and commercialize products under the previous strategic alliance agreements terminated, resulting in the return to us of worldwide rights to all product candidates that had previously been covered by the strategic alliance.
		•	We have no further obligation to provide research and development services to Mundipharma and Purdue as of July 17, 2012.
		•	Mundipharma and Purdue have no further obligation to provide research and development funding to us. Under the strategic alliance, Mundipharma was obligated to reimburse us for research and development expenses we incurred, up to an annual aggregate cap for each strategic alliance program other than FAAH. We did not record a liability for amounts previously funded by Purdue and Mundipharma as this relationship was not considered a financing arrangement.
		•	We are obligated to pay Mundipharma and Purdue a 4% royalty in the aggregate, subject to reduction as described below, on worldwide net sales of products that were covered by the alliance until such time as they have recovered approximately $260 million, representing the research and development funding paid to us for research and development services performed by us through the termination of the strategic alliance. After this cost recovery, our royalty obligations to Mundipharma and Purdue will be reduced to a 1% royalty on net sales in the United States of products that were previously subject to the strategic alliance. All payments are contingent upon the successful commercialization of products subject to the alliance, which products are subject to significant further development. As such, there is significant uncertainty about whether any such products will ever be approved or commercialized. If no products are commercialized, no payments will be due by us to Mundipharma and Purdue; therefore, no amounts have been accrued.
	Royalties are payable under these agreements until the later to occur of the last-to-expire of specified patent rights and the expiration of non-patent regulatory exclusivities in a country, provided that if royalties are payable solely on the basis of non-patent regulatory exclusivity, each of the royalty rates is reduced by 50%. In addition, royalties payable under these agreements after Mundipharma and Purdue have recovered all research and development expenses paid to us are subject to reduction on account of third-party royalty payments or patent litigation damages or settlements which might be required to be paid by us if litigation were to arise, with any such reductions capped at 50% of the amounts otherwise payable during the applicable royalty payment period.
	The 2012 termination agreements resulted in a gain on termination of Purdue entities alliance and a positive net income impact of $46.6 million, or a decrease of $1.47 in basic and diluted loss per share for the year ended December 31, 2012.
	Accounting Impact of Alliance Termination, Debt Extinguishment and Sale and Issuance of Common Stock
	We recorded the following during the year ended December 31, 2012:
		•	gain on termination of Purdue entities strategic alliance of $46.6 million;
		•	additional equity on our balance sheet of $74.4 million;
		•	extinguishment of $39.5 million of debt on balance sheet;
		•	elimination of $54.0 million of deferred revenue on balance sheet; and
		•	additional cash of $27.5 million.
	We considered the fact that certain elements of the arrangement discussed above closed before others, despite the fact that all of the elements were negotiated and signed concurrently in contemplation of one another. In particular, the strategic alliance with Mundipharma and Purdue was terminated on July 17, 2012, and therefore, there are no further deliverables required under those agreements. However, the equity offering and debt extinguishment did not close at that time because certain regulatory events outside of our control had to occur prior to the closing. As a result, we evaluated the termination of the strategic alliance separately from the financing transaction, including the extinguishment of debt and sale and issuance of stock. We recorded the gain on termination of the Mundipharma and Purdue strategic alliance for $46.6 million, which represented our past performance under the 2008 collaboration because we have no further obligation to provide research and development, and the financial risk associated with the research and development has been transferred to the Purdue entities. In particular, any payment of royalties to Mundipharma and Purdue are conditional on the future commercialization of our product candidates.
	To establish the financial impact of the stock issuance and debt extinguishment, we determined both the fair value of the common stock we sold and issued and the debt and accrued interest extinguished. We consider Mundipharma and Purdue to be related parties for financial reporting purposes because of their equity ownership. Therefore, we recorded the difference between extinguishing the fair value of the debt and accrued interest, the sale and issuance of our common stock and receiving $27.5 million in cash in additional paid-in capital.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2014
Income Taxes	13. Income Taxes
	Our income tax expense for the year ended December 31, 2014 of $0.2 million consisted primarily of current US federal taxes. We had no income tax expense or benefit for the years ended December 31, 2013 and 2012.
	Our income tax expense for the years ended December 31, 2014, 2013 and 2012 differed from the expected U.S. federal statutory income tax expense as set forth below:
		2014			2013			2012
		(in thousands)
	Expected federal tax expense (benefit)	$	(5,872	)	$	(43,105	)	$	(18,348	)
	Permanent differences		3,537			2,681			(4,685	)
	State taxes, net of the deferred federal benefit		(912	)		(6,694	)		(2,849	)
	Tax credit carryforwards		(9,510	)		(11,534	)		(589	)
	Adjustments to deferred tax assets and deferred tax liabilities		776			129			3,371
	Alternative minimum tax		183			—			—
	Other		79			62			34
	Change in valuation allowance		11,902			58,461			23,066
	Income tax expense	$	183		$	—		$	—
	The significant components of our deferred tax assets are as follows:
		Year Ended December 31,
		2014			2013
		(in thousands)
	Deferred tax assets:
	Net operating loss carryforwards	$	133,180		$	136,879
	Tax credit carryforwards		37,278			27,768
	Intangible assets		16,250			13,413
	Accrued expenses		2,666			194
	Stock-based compensation		10,031			9,842
	Other		1,428			715
	Valuation allowance		(200,833	)		(188,811	)
	Net deferred tax assets	$	—		$	—
	We have recorded a valuation allowance against our deferred tax assets in each of the years ended December 31, 2014, 2013 and 2012 because management believes that it is more likely than not that these assets will not be realized. The valuation allowance increased by approximately $12.0 million during the year ended December 31, 2014 primarily as a result of increases in unbenefited deferred tax assets such as tax credits and intangible assets. The valuation allowance increased by approximately $59.1 million during the year ended December 31, 2013 primarily as a result of increases in unbenefited deferred tax assets such as tax losses and credits. The valuation allowance increased by approximately $24.2 million during the year ended December 31, 2012 primarily as a result of increases in unbenefited deferred tax assets such as tax losses and credits and intangible assets.
	Subject to the limitations described below, at December 31, 2014, we had cumulative net operating loss carryforwards of approximately $386.3 million and $270.1 million available to reduce federal and state taxable income, which expire through 2034, and have begun to expire and expire through 2034, respectively. In addition, we have cumulative federal and state tax credit carryforwards of $31.2 million and $9.2 million, respectively, available to reduce federal and state income taxes which expire through 2034 and 2029, respectively. The net operating loss carryforwards include approximately $36.5 million of deductions related to the exercise of stock options. This amount represents an excess tax benefit and has not been included in the gross deferred tax asset reflected for net operating losses nor the cumulative net operating loss carryforward disclosures above. Additionally, 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, 2014 and 2013, we had no unrecognized tax benefits. As of December 31, 2014, 2013 and 2012, 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.
	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 2011, although carryforward attributes that were generated prior to tax year 2011 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, 2014
Stockholders' Equity	14. Stockholders’ Equity
	Common Stock Offerings
	In August 2012, we completed an underwritten public offering of 6,095,000 shares of common stock, which were sold at a price of $14.50 per share. This offering resulted in $82.8 million of net proceeds. In December 2012, we completed an underwritten public offering of 6,551,461 shares of common stock, which were sold at a price of $26.33 per share. This offering resulted in $162.0 million of net proceeds. Related legal and accounting fees for both offerings were recorded as an offset to additional paid-in capital.
	Warrants
	In July 2002, IPI issued warrants to purchase shares of convertible preferred stock, which subsequently in the DPI merger became warrants to purchase shares of common stock in the DPI merger, in conjunction with the entry into our facility lease. At December 31, 2012, warrants to purchase 50,569 shares of our common stock were outstanding. All of these outstanding warrants were exercised in January 2013 at $13.35 per share.
	In connection with the execution of the 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. See note 9 for additional details related to the Facility Agreement.

Income_from_Massachusetts_Tax_

Income from Massachusetts Tax Incentive Award	12 Months Ended
	Dec. 31, 2014
Income from Massachusetts Tax Incentive Award	15. Income from Massachusetts Tax Incentive Award
	During the year ended December 31, 2012, we recognized $0.2 million as other income, which related to a tax grant we were awarded in 2009 from the Commonwealth of Massachusetts. The total award was approximately $0.5 million and was earned over a five year period based on our achieving certain headcount growth levels each year. We achieved the required headcount growth levels for the first two years and therefore recognized a pro rata portion of the grant in the year ended December 31, 2012. However, we did not meet the required headcount level in the third year and were required to repay the remaining $0.3 million to the Commonwealth of Massachusetts in 2013. As the award is not related to our ordinary course of operations, we have recorded the amount as other income.

Restructuring_Activities

Restructuring Activities	12 Months Ended
	Dec. 31, 2014
Restructuring Activities	16. Restructuring Activities
	In June 2012, we voluntarily stopped all company-sponsored clinical trials of saridegib, our Hedgehog pathway inhibitor. In July 2012, we restructured our strategic alliance agreement with Mundipharma and Purdue such that we are no longer entitled to research and development funding (see note 12), and therefore we undertook a subsequent workforce reduction.
	The associated restructuring expenses were recorded as research and development and general and administrative expenses. We recorded a restructuring expense of $2.6 million during the year ended December 31, 2012. The remaining balance payable as of December 31, 2012 was $0.4 million related to employee severance, benefits and related costs. All amounts have been paid as of December 31, 2014.

Defined_Contribution_Benefit_P

Defined Contribution Benefit Plan	12 Months Ended
	Dec. 31, 2014
Defined Contribution Benefit Plan	17. 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, 2014, 2013 and 2012, we matched 50% of the first 6% of participant contributions with shares of our common stock. Our matching contributions during the years ended December 31, 2014, 2013 and 2012 were $0.7 million each year.

Quarterly_Financial_Informatio

Quarterly Financial Information (unaudited)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information (unaudited)	18. Quarterly Financial Information (unaudited)
		Quarter Ended			Quarter Ended			Quarter Ended			Quarter Ended
		March 31, 2014			June 30, 2014			September 30, 2014			December 31, 2014
		(in thousands, except shares and per share amounts)
	Collaboration revenue	$	—		$	—		$	160,639		$	4,356
	Operating expenses:
	Research and development		34,491			28,165			44,895			36,082
	General and administrative		6,804			7,057			8,042			7,382
	Total operating expenses		41,295			35,222			52,937			43,464
	Income (loss) from operations		(41,295	)		(35,222	)		107,702			(39,108	)
	Other income (expenses):
	Interest expense		(1,139	)		(2,938	)		(4,537	)		(1,035	)
	Interest and investment income		168			136			52			(17	)
	Total other income (expense)		(971	)		(2,802	)		(4,485	)		(1,052	)
	Loss before income taxes		(42,266	)		(38,024	)		103,217			(40,160	)
	Income tax		—			—			—			(183	)
	Net income (loss)	$	(42,266	)	$	(38,024	)	$	103,217		$	(40,343	)
	Income (loss) per common share:
	Basic	$	(0.87	)	$	(0.78	)	$	2.08		$	(0.83	)
	Diluted	$	(0.87	)	$	(0.78	)	$	2.03		$	(0.83	)
	Weighted average number of common shares outstanding:
	Basic		48,348,767			48,543,853			48,632,888			48,788,917
	Diluted		48,348,767			48,543,853			49,735,303			48,788,917
		Quarter Ended			Quarter Ended			Quarter Ended			Quarter Ended
		March 31, 2013			June 30, 2013			September 30, 2013			December 31, 2013
		(in thousands, except shares and per share amounts)
	Operating expenses:
	Research and development	$	20,231		$	26,080		$	26,857		$	26,592
	General and administrative		7,430			6,675			7,319			6,492
	Total operating expenses		27,661			32,755			34,176			33,084
	Loss from operations		(27,661	)		(32,755	)		(34,176	)		(33,084	)
	Other income:
	Interest and investment income		335			164			238			159
	Total other income		335			164			238			159
	Net loss	$	(27,326	)	$	(32,591	)	$	(33,938	)	$	(32,925	)
	Basic and diluted net loss per common share	$	(0.57	)	$	(0.68	)	$	(0.71	)	$	(0.68	)
	Basic and diluted weighted average number of common shares outstanding		47,620,147			47,915,726			48,052,939			48,114,922

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2014
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.
Reclassifications	Reclassifications
	Certain amounts in the prior years’ financial statements have been reclassified to conform with the current-year presentation. These reclassifications have no impact on previously reported net income, net loss or cash flows.
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, U.S. government-sponsored enterprise obligations, corporate obligations and mortgage-backed securities. Corporate obligations include obligations issued by corporations in countries other than the United States, including some obligations that have not been guaranteed by governments and government agencies. 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, 2014 and 2013 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 interest and investment 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. government-sponsored enterprise obligations, investment grade corporate obligations and mortgage-backed securities. 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 discovery and 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 amortization of the deferred revenue associated with the grant of rights and licenses to, and reimbursed research and development services provided to, Mundipharma International Corporation Limited, or Mundipharma, and Purdue Pharmaceutical Products L.P., or Purdue, accounted for all of our revenue during the year ended December 31, 2012. We did not record any revenue in the year ended December 31, 2013 due to the termination of our strategic alliance with Mundipharma and Purdue on July 17, 2012, (see note 12).
	We considered Mundipharma, Purdue and their respective associated entities to be related parties for financial reporting purposes prior to April 2013 because of their equity ownership in us (see note 12).
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. Assets included in construction in process are not depreciated until placed into service. 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 and capital leases are included in depreciation expense. 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:
	Laboratory equipment		5 years
	Computer equipment and software		3 to 5 years
	Leasehold improvements		Shorter of lease term or useful life of asset
	Furniture and fixtures		7 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. We value the balance of the release payment due to Takeda based on a discounted cash flow model (see note 12).
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 applicable milestone over the remaining period of performance.
	We will recognize royalty revenue, if any, based upon actual and estimated net sales by the licensee of licensed products in licensed territories, and in the period the sales occur. We have not recognized any royalty revenue to date.
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.
	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, 2014 and 2013.
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. 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 (the proceeds of which are then assumed to have been used to repurchase outstanding stock using the treasury stock method) and the exercise of outstanding warrants. 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. Common equivalent shares have not been included in the net loss per share calculations for the periods presented because the effect of including them would have been anti-dilutive. Total potential gross common equivalent shares consisted of the following:
			At December 31,
			2014		2013		2012
	Stock options			6,577,296		6,083,318		5,574,527
	Warrants			1,000,000		—		50,569
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. During the year ended December 31, 2014, there were no reclassifications out of accumulated other comprehensive income (loss).
Stock-Based Compensation Expense	Stock-Based Compensation Expense
	For awards granted to employees and directors, including our 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, and recognize the expense over the requisite service period on a straight-line basis. We have no awards with market conditions.
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 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 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 we record the reimbursement as revenue. 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, as was the case with our agreement with Intellikine, Inc., or Intellikine, we record the reimbursement or the achievement of the development milestone as research and development expense. In January 2012, Intellikine was acquired by Takeda Pharmaceutical Company Limited, or Takeda, acting through its Millennium business unit. We refer to our phosphoinositide-3-kinase, or PI3K, program licensor as Takeda

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2014
Property and Equipment, Depreciated Periods	Property and equipment are depreciated over the following periods:
	Laboratory equipment	5 years
	Computer equipment and software	3 to 5 years
	Leasehold improvements	Shorter of lease term or useful life of asset
	Furniture and fixtures	7 years
Total Potential Gross Common Equivalent Shares	Total potential gross common equivalent shares consisted of the following:
		At December 31,
		2014		2013		2012
	Stock options		6,577,296		6,083,318		5,574,527
	Warrants		1,000,000		—		50,569

StockBased_Compensation_Tables

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2014
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,
		2014			2013			2012
		(in thousands)
	Research and development	$	7,502		$	6,213		$	3,177
	General and administrative		5,086			5,942			4,634
Black-Scholes Valuation Model, Weighted-Average Assumptions for Stock Options	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:
		Year Ended
		December 31,
		2014			2013			2012
	Risk-free interest rate		1.7	%		1.1	%		1.1	%
	Expected annual dividend yield		—			—			—
	Expected stock price volatility		70.9	%		64.6	%		63.3	%
	Expected term of options		5.0 years			5.4 years			6.1 years
Summary of Stock Option Activity	A summary of our stock option activity for the year ended December 31, 2014 is as follows:
		Stock Options			Weighted-Average			Weighted-Average			Aggregate
					Exercise Price			Remaining  Contractual			Intrinsic Value
								Life			(in millions)
								(years)
	Outstanding at January 1, 2014		6,083,318		$	14.04
	Granted		1,576,734			12.6
	Exercised		(523,954	)		7.41
	Forfeited		(558,802	)		19.53
	Outstanding at December 31, 2014		6,577,296		$	13.76			6.3		$	37.5
	Vested or expected to vest at December 31, 2014		6,274,310		$	13.59			6.1		$	36.5
	Exercisable at December 31, 2014		4,704,549		$	12.08			5.3		$	31.1
Black-Scholes Valuation Model, Weighted-Average Assumptions for Employee Stock Purchase Plan	For the years ended December 31, 2014 and 2013, the fair values were estimated using the Black-Scholes valuation model using the following weighted-average assumptions:
		December 31, 2014			December 31, 2013
	Risk-free interest rate		0.3	%		0.3	%
	Expected annual dividend yield		—			—
	Expected stock price volatility		66.7	%		91.5	%
	Expected term of options		1.25 years			1.25 years

Cash_Cash_Equivalents_and_Avai1

Cash, Cash Equivalents and Available-for-Sale Securities (Tables)	12 Months Ended
	Dec. 31, 2014
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, 2014
		Cost		Gross		Gross			Estimated
				Unrealized		Unrealized			Fair Value
				Gains		Losses
		(in thousands)
	Cash and cash equivalents due in 90 days or less	$	307,405	$	—	$	—		$	307,405
	Available-for-sale securities:
	Corporate obligations due in one year or less		21,324		6		(1	)		21,329
	Mortgage-backed securities due after ten years		412		107		—			519
	U.S. government-sponsored enterprise obligations due in one year or less		3,990		2		—			3,992
	Total available-for-sale securities		25,726		115		(1	)		25,840
	Total cash, cash equivalents and available-for-sale securities	$	333,131	$	115	$	(1	)	$	333,245
		December 31, 2013
		Cost		Gross		Gross			Estimated
				Unrealized		Unrealized			Fair Value
				Gains		Losses
		(in thousands)
	Cash and cash equivalents due in 90 days or less	$	68,114	$	—	$	—		$	68,114
	Available-for-sale securities:
	Corporate obligations due in one year or less		103,889		18		(16	)		103,891
	Corporate obligations due in one to five years		13,513		32		—			13,545
	Mortgage-backed securities due after ten years		478		104		—			582
	U.S. government-sponsored enterprise obligations due in one year or less		24,144		13		—			24,157
	U.S. government-sponsored enterprise obligations due in one to five years		4,174		5		—			4,179
	Total available-for-sale securities		146,198		172		(16	)		146,354
	Total cash, cash equivalents and available-for-sale securities	$	214,312	$	172	$	(16	)	$	214,468

Fair_Value_Tables

Fair Value (Tables)	12 Months Ended
	Dec. 31, 2014
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, 2014:
		Level 1		Level 2
		(in thousands)
	Assets:
	Cash and cash equivalents	$	256,559	$	50,846
	Corporate obligations (including commercial paper)		—		21,329
	Mortgage-backed securities		—		519
	U.S. government-sponsored enterprise obligations		—		3,992
	Total	$	256,559	$	76,686

Prepaid_expenses_and_other_cur1

Prepaid expenses and other current assets (Tables)	12 Months Ended
	Dec. 31, 2014
Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consist of the following:
		December 31,
		2014		2013
		(in thousands)
	Prepaid comparator drug	$	5,085	$	6,673
	Prepaid expenses		4,124		2,044
	Other current assets		1,986		2,338
	Total prepaid expenses and other current assets	$	11,195	$	11,055

Property_and_Equipment_Tables

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2014
Summary of Property and Equipment	Property and equipment consist of the following:
		December 31,
		2014			2013
		(in thousands)
	Laboratory equipment	$	12,615		$	14,958
	Computer hardware and software		5,550			6,488
	Office equipment and furniture and fixtures		720			872
	Construction in process		16,004			—
	Leasehold improvements		5,041			4,982
			39,930			27,300
	Less accumulated depreciation		(20,960	)		(23,290	)
		$	18,970		$	4,010

Accrued_Expenses_Tables

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2014
Accrued Expenses	Accrued expenses consisted of the following:
		December 31,
		2014		2013
		(in thousands)
	Accrued compensation and benefits	$	7,353	$	1,839
	Accrued drug manufacturing costs		1,280		991
	Accrued clinical studies		5,134		4,009
	Accrued preclinical studies		543		303
	Facility fee		1,500		—
	Other		1,958		2,022
	Total accrued expenses	$	17,768	$	9,164

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2014
Future Minimum Payments Under Facility Leases	Future minimum payments, excluding operating costs and taxes, under the two lease agreements described above are as follows:
		784 Facility Lease		780/790 Facility Lease
		(in thousands)
	Years Ending December 31:
	2015	$	1,362	$	2,792
	2016		2,044		3,556
	2017		2,044		3,470
	2018		2,044		3,516
	2019		2,044		3,840
	2020 and beyond		11,947		20,161
	Total minimum lease payments	$	21,485	$	37,335

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income Tax Benefit or Expense	Our income tax expense for the years ended December 31, 2014, 2013 and 2012 differed from the expected U.S. federal statutory income tax expense as set forth below:
		2014			2013			2012
		(in thousands)
	Expected federal tax expense (benefit)	$	(5,872	)	$	(43,105	)	$	(18,348	)
	Permanent differences		3,537			2,681			(4,685	)
	State taxes, net of the deferred federal benefit		(912	)		(6,694	)		(2,849	)
	Tax credit carryforwards		(9,510	)		(11,534	)		(589	)
	Adjustments to deferred tax assets and deferred tax liabilities		776			129			3,371
	Alternative minimum tax		183			—			—
	Other		79			62			34
	Change in valuation allowance		11,902			58,461			23,066
	Income tax expense	$	183		$	—		$	—
Significant Components of Deferred Tax Assets	The significant components of our deferred tax assets are as follows:
		Year Ended December 31,
		2014			2013
		(in thousands)
	Deferred tax assets:
	Net operating loss carryforwards	$	133,180		$	136,879
	Tax credit carryforwards		37,278			27,768
	Intangible assets		16,250			13,413
	Accrued expenses		2,666			194
	Stock-based compensation		10,031			9,842
	Other		1,428			715
	Valuation allowance		(200,833	)		(188,811	)
	Net deferred tax assets	$	—		$	—

Quarterly_Financial_Informatio1

Quarterly Financial Information (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information
		Quarter Ended			Quarter Ended			Quarter Ended			Quarter Ended
		March 31, 2014			June 30, 2014			September 30, 2014			December 31, 2014
		(in thousands, except shares and per share amounts)
	Collaboration revenue	$	—		$	—		$	160,639		$	4,356
	Operating expenses:
	Research and development		34,491			28,165			44,895			36,082
	General and administrative		6,804			7,057			8,042			7,382
	Total operating expenses		41,295			35,222			52,937			43,464
	Income (loss) from operations		(41,295	)		(35,222	)		107,702			(39,108	)
	Other income (expenses):
	Interest expense		(1,139	)		(2,938	)		(4,537	)		(1,035	)
	Interest and investment income		168			136			52			(17	)
	Total other income (expense)		(971	)		(2,802	)		(4,485	)		(1,052	)
	Loss before income taxes		(42,266	)		(38,024	)		103,217			(40,160	)
	Income tax		—			—			—			(183	)
	Net income (loss)	$	(42,266	)	$	(38,024	)	$	103,217		$	(40,343	)
	Income (loss) per common share:
	Basic	$	(0.87	)	$	(0.78	)	$	2.08		$	(0.83	)
	Diluted	$	(0.87	)	$	(0.78	)	$	2.03		$	(0.83	)
	Weighted average number of common shares outstanding:
	Basic		48,348,767			48,543,853			48,632,888			48,788,917
	Diluted		48,348,767			48,543,853			49,735,303			48,788,917
		Quarter Ended			Quarter Ended			Quarter Ended			Quarter Ended
		March 31, 2013			June 30, 2013			September 30, 2013			December 31, 2013
		(in thousands, except shares and per share amounts)
	Operating expenses:
	Research and development	$	20,231		$	26,080		$	26,857		$	26,592
	General and administrative		7,430			6,675			7,319			6,492
	Total operating expenses		27,661			32,755			34,176			33,084
	Loss from operations		(27,661	)		(32,755	)		(34,176	)		(33,084	)
	Other income:
	Interest and investment income		335			164			238			159
	Total other income		335			164			238			159
	Net loss	$	(27,326	)	$	(32,591	)	$	(33,938	)	$	(32,925	)
	Basic and diluted net loss per common share	$	(0.57	)	$	(0.68	)	$	(0.71	)	$	(0.68	)
	Basic and diluted weighted average number of common shares outstanding		47,620,147			47,915,726			48,052,939			48,114,922

Summary_of_Significant_Account3

Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014
	Segment
Significant Accounting Policies [Line Items]
Number of operating segments	1
Reclassifications out of accumulated other comprehensive income loss	$0

Property_and_Equipment_Depreci

Property and Equipment, Depreciation Periods (Detail)	12 Months Ended
	Dec. 31, 2014
Laboratory Equipment
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful lives	5 years
Computer Equipment and Software | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful lives	3 years
Computer Equipment and Software | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful lives	5 years
Leasehold Improvements
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful lives	Shorter of lease term or useful life of asset
Furniture and Fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful lives	7 years

Summary_Of_Outstanding_Shares_

Summary Of Outstanding Shares Of Common Stock Equivalents Excluded From Computation Of Net Income (Loss) Per Share Attributable To Common Stockholders (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common equivalent shares excluded from computation of earnings per share, amount	6,577,296	6,083,318	5,574,527
Warrants (excluded from treasury stock method)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common equivalent shares excluded from computation of earnings per share, amount	1,000,000		50,569

StockBased_Compensation_Additi

Stock-Based Compensation - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from purchase of common stock	$836,000	$374,000
Unrecognized compensation cost, net of estimated forfeitures, related to unvested stock options and awards under ESPP	17,100,000
Unrecognized compensation cost, weighted-average recognition period	2 years 2 months 12 days
Weighted Average Forfeiture Rate	14.00%	13.00%	12.00%
Weighted Average Fair Value per share of Option Granted	$7.45	$18.07	$6
Aggregate intrinsic value of options exercised	4,000,000	16,000,000	34,100,000
Cash received from stock option exercises	3,881,000	5,299,000	21,386,000
Income tax benefits	0	0	0
Consulting agreement period			3 years
Non-employee stock-based compensation expense		700,000	1,200,000
Other Postretirement Benefit Plans, Defined Benefit
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees terminated	1
Additional Stock Based Compensation Expense	400,000
Stock Incentive Plans Under, the 2010 Plan, the 2000 Plan and the 2001 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of Shares Vested	25.00%
Remaining Percentage of Shares Vested	75.00%
Annual grants vesting period	4 years
Stock options granted, expiration period	10 years
2010 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock Issued pursuant to Awards Granted	6,000,000
Common Stock Reserved for Issuance upon exercise of Outstanding Awards	4,113,803
Maximum Common Stock that can be issued pursuant to Awards Granted	2,903,202
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	2,420,345
2001 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock Reserved for Issuance upon exercise of Outstanding Awards	43,148
2013 ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of common stock purchase price		85.00%
Common stock offering aggregate period		24 months
Number of common stock purchase period		4
Common stock offering purchase period		6 months
Number of common stock purchased	76,572	31,903
Proceeds from purchase of common stock	800,000	400,000
Directors Compensation Plan | Other Postretirement Benefit Plans, Defined Benefit
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of members of retired	2		2
Share based compensation extended exercising period for vested stock options	6 months		2 years
Additional Stock Based Compensation Expense			$300,000
Share based compensation exercising period for vested stock options			90 days
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value per share of ESPP granted	$5.66	$8.68

Stock_Based_Compensation_Expen

Stock Based Compensation Expense, Related to All Equity Awards (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Research and Development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Effect of stock-based compensation on net loss	$7,502	$6,213	$3,177
General and Administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Effect of stock-based compensation on net loss	$5,086	$5,942	$4,634

BlackScholes_Valuation_Model_W

Black-Scholes Valuation Model, Weighted-Average Assumptions (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.70%	1.10%	1.10%
Expected annual dividend yield	0.00%	0.00%	0.00%
Expected stock price volatility	70.90%	64.60%	63.30%
Expected term of options	5 years	5 years 4 months 24 days	6 years 1 month 6 days
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	0.30%	0.30%
Expected annual dividend yield	0.00%	0.00%
Expected stock price volatility	66.70%	91.50%
Expected term of options	1 year 3 months	1 year 3 months

Summary_of_Stock_Option_Activi

Summary of Stock Option Activity (Detail) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014
Stock Options
Outstanding at beginning of period	6,083,318
Granted	1,576,734
Exercised	-523,954
Forfeited	-558,802
Outstanding at end of period	6,577,296
Vested or expected to vest at end of period	6,274,310
Exercisable at end of period	4,704,549
Weighted-Average Exercise Price
Outstanding at beginning of period	$14.04
Granted	$12.60
Exercised	$7.41
Forfeited	$19.53
Outstanding at end of period	$13.76
Vested or expected to vest at end of Period	$13.59
Exercisable at end of Period	$12.08
Weighted-Average Remaining Contractual Life (years)
Outstanding	6 years 3 months 18 days
Vested or expected to vest at end of period	6 years 1 month 6 days
Exercisable at end of period	5 years 3 months 18 days
Aggregate Intrinsic Value
Outstanding at end of period	$37.50
Vested or expected to vest at end of period	36.5
Exercisable at end of period	$31.10

Summary_of_Cash_Cash_Equivalen

Summary of Cash, Cash Equivalents and Available-for-sale Securities (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents due in 90 days or less, Cost	$307,405,000	$68,114,000
Cash and cash equivalents due in 90 days or less, Gross Unrealized Gains	0	0
Cash and cash equivalents due in 90 days or less, Gross Unrealized Losses	0	0
Cash and cash equivalents due in 90 days or less, Estimated Fair Value	307,405,000	68,114,000	175,742,000	24,197,000
Total available-for-sale securities, Cost	25,726,000	146,198,000
Total available-for-sale securities, Gross Unrealized Gains	115,000	172,000
Total available-for-sale securities, Gross Unrealized Losses	-1,000	-16,000
Total available-for-sale securities, Estimated Fair Value	25,840,000	146,354,000
Total cash, cash equivalents and available-for-sale securities, Cost	333,131,000	214,312,000
Total cash, cash equivalents and available-for-sale securities, Gross Unrealized Gains	115,000	172,000
Total cash, cash equivalents and available-for-sale securities, Gross Unrealized Losses	-1,000	-16,000
Total cash, cash equivalents and available-for-sale securities, Estimated Fair Value	333,245,000	214,468,000
Mortgage-Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities due after ten years, Cost	412,000	478,000
Available-for-sale securities due after ten years, Gross Unrealized Gains	107,000	104,000
Available-for-sale securities, after ten years, Gross Unrealized Losses	0	0
Available-for-sale securities due after ten years, Estimated Fair Value	519,000	582,000
Corporate Obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, due in one year or less, Cost	21,324,000	103,889,000
Available-for-sale securities, due in one year or less, Gross Unrealized Gains	6,000	18,000
Available-for-sale securities, due in one year or less, Gross Unrealized Losses	-1,000	-16,000
Available-for-sale securities, due in one year or less, Estimated Fair Value	21,329,000	103,891,000
Available-for-sale securities, due in one to five years, Cost		13,513,000
Available-for-sale securities, due in one to five years, Gross Unrealized Gains		32,000
Available-for-sale securities, due in one to five years, Gross Unrealized Losses		0
Available-for-sale securities, due in one to five years, Estimated Fair Value		13,545,000
U.S. Government Sponsored Enterprise Obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, due in one year or less, Cost	3,990,000	24,144,000
Available-for-sale securities, due in one year or less, Gross Unrealized Gains	2,000	13,000
Available-for-sale securities, due in one year or less, Estimated Fair Value	3,992,000	24,157,000
Available-for-sale securities, due in one to five years, Cost		4,174,000
Available-for-sale securities, due in one to five years, Gross Unrealized Gains		5,000
Available-for-sale securities, due in one to five years, Gross Unrealized Losses		0
Available-for-sale securities, due in one to five years, Estimated Fair Value		$4,179,000

Cash_Cash_Equivalents_and_Avai2

Cash, Cash Equivalents and Available-for-Sale Securities - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities debt fair value	$15,000,000
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	4
Foreign Financial Institution and Other Corporate Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities number of financial institution debt securities and other corporate debt securities located in foreign countries	6
Available for sale securities debt fair value	$50,700,000

Assets_Carried_at_Fair_Value_M

Assets Carried at Fair Value Measured on Recurring Basis (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$256,559
Level 1 | Cash and cash equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	256,559
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	76,686
Level 2 | Cash and cash equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	50,846
Level 2 | Corporate obligations (including commercial paper)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	21,329
Level 2 | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	519
Level 2 | U.S. government-sponsored enterprise obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$3,992

Fair_Value_Additional_Informat

Fair Value - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities	$25,840,000	$146,354,000
Transfers of assets or liabilities between Level 1 and Level 2	0
Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities	0	0
Payment at Fair value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Due to Takeda, Fair value	$6,700,000
Maximum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Maturity of highly liquid investments	3 months

Recovered_Sheet1

Prepaid Expenses and Other Current Assets (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Prepaid Expenses And Other Current Assets [Line Items]
Prepaid comparator drug	$5,085	$6,673
Prepaid expenses	4,124	2,044
Other current assets	1,986	2,338
Total prepaid expenses and other current assets	$11,195	$11,055

Summary_of_Property_and_Equipm

Summary of Property and Equipment (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Property, Plant and Equipment [Line Items]
Property Plant And Equipment, Gross	$39,930	$27,300
Less accumulated depreciation	-20,960	-23,290
Property Plant And Equipment, Net	18,970	4,010
Laboratory Equipment
Property, Plant and Equipment [Line Items]
Property Plant And Equipment, Gross	12,615	14,958
Computer Equipment and Software
Property, Plant and Equipment [Line Items]
Property Plant And Equipment, Gross	5,550	6,488
Office Equipment Furniture And Fixtures
Property, Plant and Equipment [Line Items]
Property Plant And Equipment, Gross	720	872
Construction in Progress
Property, Plant and Equipment [Line Items]
Property Plant And Equipment, Gross	16,004
Leasehold Improvements
Property, Plant and Equipment [Line Items]
Property Plant And Equipment, Gross	$5,041	$4,982

Property_and_Equipment_Additio

Property and Equipment - Additional Information (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Capitalized cost on internally developed software		$400,000
Depreciation expense associated with internally developed software	100,000	49,000
Building
Property, Plant and Equipment [Line Items]
Construction in process	$14,700,000

Restricted_Cash_Additional_Inf

Restricted Cash - Additional Information (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted Cash	$1.70	$1.10

Debt_Facility_Agreement_Additi

Debt Facility Agreement - Additional Information (Detail) (USD $)	0 Months Ended	12 Months Ended
	Feb. 24, 2014	Dec. 31, 2014	Sep. 22, 2014	Feb. 24, 2014
Debt Instrument [Line Items]
Line Of credit facility maximum borrowing capacity	$100,000,000		$50,000,000	$100,000,000
Minimum draw down during the 12 months following effective date	25,000,000			25,000,000
Number of business days needed as prior notice for loan commitment	22 days
Percentage of fee to be paid on undrawn portion		3.00%
Facility fee	3,000,000	1,500,000
Common stock warrants issued, exercise price	$13.83			$13.83
Total cost of securing loan commitment		11,800,000
Fair value of the warrants issued		8,400,000
Common stock warrants issued	1,000,000			1,000,000
Transaction cost		400,000
Facility fee reduction rate		50.00%
Reduction rate in borrowing capacity		50.00%
Reduction rate in loan commitment asset outstanding		50.00%
Additional expense as a result of reduction in remaining loan commitment asset outstanding		1,800,000
Interest expense associated with amortization and write-off of the loan commitment asset		$9,600,000
Deerfield
Debt Instrument [Line Items]
Ownership percentage		9.99%

Accrued_Expenses_Detail

Accrued Expenses (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Accrued Expenses [Line Items]
Accrued compensation and benefits	$7,353	$1,839
Accrued drug manufacturing costs	1,280	991
Accrued clinical studies	5,134	4,009
Accrued preclinical studies	543	303
Facility fee	1,500
Other	1,958	2,022
Total accrued expenses	$17,768	$9,164

Recovered_Sheet2

Commitments And Contingencies - Additional Information (Detail) (USD $)	0 Months Ended	12 Months Ended			0 Months Ended
	Sep. 25, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Nov. 06, 2014
		Leases			Right
					sqft
Operating Lease Agreements [Line Items]
Number of lease agreements		2
Area of premises leased under lease agreement					54,861
Letters of credit, outstanding amount	$1,000,000	$1,000,000
Potential reduction of letter of credit	750,000
Payment made for repairs and updates	5,856,100
Building and accumulated construction costs		16,000,000
Construction liability		15,456,000
Lease rent expense		4,700,000	4,700,000	4,800,000
Rent free period		5 months
Lease facility prepaid rent		170,292
Bank fee		30,000
Sublease income		200,000	200,000	700,000
Sublease expiration period month and year		2016-01
Future minimum sublease income for the year ended December 2015		200,000
From the Commencement Date until April 1, 2015
Operating Lease Agreements [Line Items]
Facilities leases, base rent per month	0
From April 1, 2015 through March 31, 2020
Operating Lease Agreements [Line Items]
Facilities leases, base rent per month	170,292
From April 1, 2020 until the Expiration Date
Operating Lease Agreements [Line Items]
Facilities leases, base rent per month	190,625
790 Memorial Drive, or the 790 Premises
Operating Lease Agreements [Line Items]
Area of premises leased under lease agreement					3,861
Lease expiration date					31-Mar-25
Number of options to extend terms of the lease					2
Extended term of lease agreement					5 years
Lease arrangement description					3,000,000
790 Memorial Drive, or the 790 Premises | February 1, 2016
Operating Lease Agreements [Line Items]
Land subject to ground leases					13,159
Base rent per square foot					69
790 Memorial Drive, or the 790 Premises | February 1, 2018
Operating Lease Agreements [Line Items]
Base rent per square foot					70
790 Memorial Drive, or the 790 Premises | Previously Leased Area
Operating Lease Agreements [Line Items]
Area of premises leased under lease agreement					17,020
780 Memorial Drive, or the 780 Premises
Operating Lease Agreements [Line Items]
Area of premises leased under lease agreement					51,000
Land
Operating Lease Agreements [Line Items]
Lease rent expense		$68,000
Lease Agreements
Operating Lease Agreements [Line Items]
Area of premises leased under lease agreement	61,000
Lease commencement date		1-Nov-14
Lease expiration date		31-Mar-25
Number of options to extend terms of the lease		2
Extended term of lease agreement		5 years
Base rent for each extension term as a percentage of fair market base rent per square foot		95.00%
Lease Agreements | Maximum
Operating Lease Agreements [Line Items]
Lease notice period		18 months
Lease Agreements | Minimum
Operating Lease Agreements [Line Items]
Lease notice period		12 months

Future_Minimum_Payments_Under_

Future Minimum Payments Under Facility Leases (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
784 Facility Lease
Operating Leased Assets [Line Items]
2015	$1,362
2016	2,044
2017	2,044
2018	2,044
2019	2,044
2020 and beyond	11,947
Total minimum lease payments	21,485
780/790 Facility Lease
Operating Leased Assets [Line Items]
2015	2,792
2016	3,556
2017	3,470
2018	3,516
2019	3,840
2020 and beyond	20,161
Total minimum lease payments	$37,335

Collaborations_Additional_Info

Collaborations - Additional Information (Detail) (USD $)	0 Months Ended	1 Months Ended	3 Months Ended								12 Months Ended			0 Months Ended		1 Months Ended
	Jul. 17, 2012	Jul. 31, 2010	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jul. 29, 2014	Sep. 02, 2014	Aug. 31, 2014	Feb. 28, 2014
											Product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development			$36,082,000	$44,895,000	$28,165,000	$34,491,000	$26,592,000	$26,857,000	$26,080,000	$20,231,000	$143,633,000	$99,760,000	$118,595,000
General and administrative expenses			7,382,000	8,042,000	7,057,000	6,804,000	6,492,000	7,319,000	6,675,000	7,430,000	29,285,000	27,916,000	27,882,000
Upfront payment received											275,000,000
Agreed level of royalty depending on annual net sales											23.50%
Agreed level of royalty depending on annual net sales											30.50%
Reduction of tiered royalty payments receivable, percentage											4.00%
Collaboration revenue			4,356,000	160,639,000							164,995,000		47,114,000
Up-front license fee		13,500,000
Number of distinct product candidates											2
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
Prior written notice for termination after the end of the research term											180 days
Royalty term and royalty rate reduction	50.00%
Royalty payment, maximum reduction	50.00%
Gain on termination of Purdue entities alliance													46,555,000
Financial effect on net income loss per share basic and diluted as result of termination of alliance with related party													($1.47)
Increase in equity													74,400,000
Extinguishment of debt													39,500,000
Deferred revenue from Purdue entities													-54,000,000
Proceeds from issuance of common stock to Purdue entities													27,500,000
Mundipharma and Purdue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Strategic Alliance Agreement Termination date											17-Jul-12
Royalty rate on future sales	4.00%
Recovery of research and development funding	260,000,000
Royalty rate payable after initial research and development cost recovery	1.00%
Royalty payable description											After this cost recovery, our royalty obligations to Mundipharma and Purdue will be reduced to a 1% royalty on net sales in the United States of products that were previously subject to the strategic alliance.
Collaboration
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development											10,000,000
Amended Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development											5,000,000
Release payment													15,000,000
Release payment, fair value													14,400,000
Amount paid on release payment during the period											6,700,000		1,700,000
Option fee														5,000,000
Exercise Fee														52,500,000
License
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment received											159,100,000
Discount rate used to determined best estimate of selling prices											11.50%
Collaboration revenue											159,100,000
Committee Services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment received											300,000
Discount rate used to determined best estimate of selling prices											11.50%
Development Services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment received											115,600,000
Discount rate used to determined best estimate of selling prices											8.00%
Development and Committee Services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue											5,900,000
Collaboration revenue recognition period											5 years
Deferred revenue			110,000,000								110,000,000
Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development															667,000,000
Development cost of distinct product candidates			5,000,000								5,000,000
Approval and commercialization cost of distinct products payable			450,000,000								450,000,000
Percent of royalty on net sale											11.00%
Maximum | Development Regulatory And Commercial Milestone
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent milestone payments			530,000,000								530,000,000
Maximum | Enrollment of Either DYNAMO or DUO
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestones payments Under the terms of the AbbVie Agreement			130,000,000								130,000,000
Maximum | Regulatory Filing and Approval Milestone
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestones payments Under the terms of the AbbVie Agreement			275,000,000								275,000,000
Maximum | Commercial Milestone
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestones payments Under the terms of the AbbVie Agreement			125,000,000								125,000,000
Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development cost of distinct product candidates																	10,000,000
Percent of royalty on net sale											7.00%
AbbVie Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
General and administrative expenses											100,000
FAAH Program License
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Ownership percentage received in exchange for licensed rights																23.00%
Gain (loss) recognized related to exchange of ownership percentage																$0

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax [Line Items]
Income Tax Benefits	$183,000	$183,000	$0	$0
Increase in Valuation Allowance		12,000,000	59,100,000	24,200,000
Available Operating Loss to carry-forward	386,300,000	386,300,000
Operating Loss available to reduce federal and state taxable income	270,100,000	270,100,000
Net Operating loss carry forward deduction related to exercise of Stock Options	36,500,000	36,500,000
Interest and penalties accrued	0	0	0	0
Unrecognized tax benefits	0	0	0
Federal
Income Tax [Line Items]
Operating loss carry-forward Expiration date		2034
Tax Credit Carry-forward Amount	31,200,000	31,200,000
Tax Credit Carry-forward, Expiration date		2034
State and Local Jurisdiction
Income Tax [Line Items]
Operating loss carry-forward Expiration date		2034
Tax Credit Carry-forward Amount	$9,200,000	$9,200,000
Tax Credit Carry-forward, Expiration date		2029

Income_Tax_Benefit_or_Expense_

Income Tax Benefit or Expense (Detail) (USD $)	3 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Components Of Income Tax Expense Benefit [Line Items]
Expected federal tax expense (benefit)		($5,872)	($43,105)	($18,348)
Permanent differences		3,537	2,681	-4,685
State taxes, net of the deferred federal benefit		-912	-6,694	-2,849
Tax credit carryforwards		-9,510	-11,534	-589
Adjustments to deferred tax assets and deferred tax liabilities		776	129	3,371
Alternative minimum tax		183
Other		79	62	34
Change in valuation allowance		11,902	58,461	23,066
Income tax expense	$183	$183	$0	$0

Significant_Components_of_Defe

Significant Components of Deferred Tax Assets (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Deferred tax assets:
Net operating loss carryforwards	$133,180	$136,879
Tax credit carryforwards	37,278	27,768
Intangible assets	16,250	13,413
Accrued expenses	2,666	194
Stock-based compensation	10,031	9,842
Other	1,428	715
Valuation allowance	-200,833	-188,811
Net deferred tax assets	$0	$0

Stockholders_Equity_Additional

Stockholders' Equity - Additional Information (Detail) (USD $)	1 Months Ended		12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2012	Aug. 31, 2012	Dec. 31, 2012	Feb. 24, 2014
Class of Stock [Line Items]
Common stock issued during period, public offering, shares	6,551,461	6,095,000
Issuance of common stock price per share	$26.33	$14.50	$26.33
Proceeds from issuance of common stock	$162	$82.80
Outstanding warrants to purchase shares of common stock			50,569
Warrant exercise date			2013-01
Warrant exercise price			$13.35
Common stock warrants issued				1,000,000
Common stock warrants issued, exercise price				$13.83

Income_from_Massachusetts_Tax_1

Income from Massachusetts Tax Incentive Award - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2009
Other Income Net [Line Items]
Income from Massachusetts tax incentive award		$193,000
Tax grant award from Commonwealth of Massachusetts			500,000
Tax grant period			5 years
Tax grant repaid	$300,000

Restructuring_Activities_Addit

Restructuring Activities - Additional Information (Detail) (Employee Severance, USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2012
Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$2.60
Restructuring charges payable	$0.40

Defined_Contribution_Benefit_P1

Defined Contribution Benefit Plan - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution	$0.70	$0.70	$0.70
Percentage of employer matching contribution	50.00%	50.00%	50.00%
Participant contributions, employee	6.00%	6.00%	6.00%

Quarterly_Financial_Informatio2

Quarterly Financial Information (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Effect of Fourth Quarter Events [Line Items]
Collaboration revenue	$4,356	$160,639							$164,995		$47,114
Operating expenses:
Research and development	36,082	44,895	28,165	34,491	26,592	26,857	26,080	20,231	143,633	99,760	118,595
General and administrative	7,382	8,042	7,057	6,804	6,492	7,319	6,675	7,430	29,285	27,916	27,882
Total operating expenses	43,464	52,937	35,222	41,295	33,084	34,176	32,755	27,661	172,918	127,676	146,477
(Loss) income from operations	-39,108	107,702	-35,222	-41,295	-33,084	-34,176	-32,755	-27,661	-7,923	-127,676	-52,808
Other income (expenses):
Interest expense	-1,035	-4,537	-2,938	-1,139					-9,649		-1,908
Interest and investment income	-17	52	136	168	159	238	164	335	339	896	559
Total other income (expense)	-1,052	-4,485	-2,802	-971	159	238	164	335	-9,310	896	-1,156
Loss before income taxes	-40,160	103,217	-38,024	-42,266					-17,233	-126,780	-53,964
Income tax	-183								-183	0	0
Net (loss) income	($40,343)	$103,217	($38,024)	($42,266)	($32,925)	($33,938)	($32,591)	($27,326)	($17,416)	($126,780)	($53,964)
Income (loss) per common share:
Basic	($0.83)	$2.08	($0.78)	($0.87)
Diluted	($0.83)	$2.03	($0.78)	($0.87)
Basic and diluted net loss per common share					($0.68)	($0.71)	($0.68)	($0.57)	($0.36)	($2.64)	($1.70)
Weighted average number of common shares outstanding:
Basic	48,788,917	48,632,888	48,543,853	48,348,767
Diluted	48,788,917	49,735,303	48,543,853	48,348,767
Basic and diluted weighted average number of common shares outstanding					48,114,922	48,052,939	47,915,726	47,620,147	48,561,653	47,936,001	31,711,264