OncoMed Pharmaceuticals 10-K 9 Mar 17 2016 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2016	Mar. 06, 2017	Jun. 30, 2016
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
Trading Symbol	OMED
Entity Registrant Name	OncoMed Pharmaceuticals Inc
Entity Central Index Key	1,302,573
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		37,398,417
Entity Public Float			$ 246,256,934

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash	$ 36,953	$ 38,444
Short-term investments	147,620	118,835
Accounts receivable and other receivables	2,515	70,699
Prepaid and other current assets	2,495	3,277
Total current assets	189,583	231,255
Property and equipment, net	4,471	4,825
Other assets	1,428	1,807
Total assets	195,482	237,887
Current liabilities:
Accounts payable	4,890	6,660
Accrued liabilities	8,599	11,475
Accrued clinical liabilities	21,854	12,221
Current portion of deferred revenue	20,510	21,543
Current portion of deferred rent		738
Liability for shares issued with repurchase rights		4
Total current liabilities	55,853	52,641
Deferred revenue, less current portion	159,373	179,612
Deferred rent, less current portion	2,917	1,729
Non-current income tax payable	367	354
Total liabilities	218,510	234,336
Commitments and contingencies (Note 7)
Stockholders’ equity (deficit):
Preferred stock, $0.001 par value; 5,000,000 shares authorized at December 31, 2016 and 2015; no shares issued and outstanding at December 31, 2016 and 2015
Common stock, $0.001 par value; 145,000,000 shares authorized at December 31, 2016 and 2015; 37,114,589 shares and 30,116,633 shares issued and outstanding at December 31, 2016 and 2015, respectively	37	30
Additional paid-in capital	389,620	313,344
Accumulated other comprehensive income	260	20
Accumulated deficit	(412,945)	(309,843)
Total stockholders’ equity (deficit)	(23,028)	3,551
Total liabilities and stockholders’ equity (deficit)	$ 195,482	$ 237,887

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2016	Dec. 31, 2015
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	145,000,000	145,000,000
Common stock, shares issued	37,114,589	30,116,633
Common stock, shares outstanding	37,114,589	30,116,633

Statements of Operations

Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue:
Collaboration revenue	$ 21,277	$ 25,216	$ 39,559
Other revenue	3,876	683
Total revenue	25,153	25,899	39,559
Operating expenses:
Research and development	109,713	92,873	76,430
General and administrative	18,827	18,583	13,753
Total operating expenses	128,540	111,456	90,183
Loss from operations	(103,387)	(85,557)	(50,624)
Interest and other income, net	299	170	105
Loss before income taxes	(103,088)	(85,387)	(50,519)
Income tax provision (benefit)	14	20	(509)
Net loss	$ (103,102)	$ (85,407)	$ (50,010)
Net loss per common share, basic and diluted	$ (3.14)	$ (2.84)	$ (1.69)
Shares used to compute net loss per common share, basic and diluted	32,859,554	30,028,684	29,664,326

Statements of Comprehensive Los

Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (103,102)	$ (85,407)	$ (50,010)
Other comprehensive income (loss):
Unrealized gains (losses) on available-for-sale securities, net of tax	240	37	(31)
Total comprehensive loss	$ (102,862)	$ (85,370)	$ (50,041)

Statements of Stockholders' Equ

Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	At-the-Market Offering [Member]	Public Offering [Member]	Common Stock [Member]	Common Stock [Member]At-the-Market Offering [Member]	Common Stock [Member]Public Offering [Member]	Additional Paid-In Capital [Member]	Additional Paid-In Capital [Member]At-the-Market Offering [Member]	Additional Paid-In Capital [Member]Public Offering [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2013	$ 118,122			$ 29			$ 292,505			$ 14	$ (174,426)
Beginning balance, shares at Dec. 31, 2013				29,397,964
Issuance of common stock upon exercise of options	$ 1,080			$ 1			1,079
Issuance of common stock upon exercise of options, shares	382,000			381,599
Issuance of common stock for ESPP purchase	$ 1,002						1,002
Issuance of commons stock for ESPP purchase, shares				65,909
Vesting of restricted stock	10						10
Vesting of restricted stock, shares				2,105
Stock-based compensation	6,194						6,194
Unrealized gain (loss) on available for sale securities	(31)									(31)
Net loss	(50,010)										(50,010)
Ending balance at Dec. 31, 2014	76,367			$ 30			300,790			(17)	(224,436)
Ending balance, shares at Dec. 31, 2014				29,847,577
Issuance of common stock upon exercise of options	$ 597						597
Issuance of common stock upon exercise of options, shares	196,000			195,696
Issuance of common stock for ESPP purchase	$ 1,181						1,181
Issuance of commons stock for ESPP purchase, shares				71,226
Vesting of restricted stock	10						10
Vesting of restricted stock, shares				2,134
Stock-based compensation	10,766						10,766
Unrealized gain (loss) on available for sale securities	37									37
Net loss	(85,407)										(85,407)
Ending balance at Dec. 31, 2015	3,551			$ 30			313,344			20	(309,843)
Ending balance, shares at Dec. 31, 2015				30,116,633
Issuance of common stock, net of offering costs		$ 4,739	$ 59,170			$ 7		$ 4,739	$ 59,163
Issuance of common stock, net of offering costs, shares					388,166	6,325,000
Issuance of common stock upon exercise of options	$ 322						322
Issuance of common stock upon exercise of options, shares	101,000			100,679
Issuance of common stock for ESPP purchase	$ 917						917
Issuance of commons stock for ESPP purchase, shares				111,633
Issuance of common stock upon release of restricted stock units, shares				71,497
Vesting of restricted stock	4						4
Vesting of restricted stock, shares				981
Stock-based compensation	11,131						11,131
Unrealized gain (loss) on available for sale securities	240									240
Net loss	(103,102)										(103,102)
Ending balance at Dec. 31, 2016	$ (23,028)			$ 37			$ 389,620			$ 260	$ (412,945)
Ending balance, shares at Dec. 31, 2016				37,114,589

Statements of Cash Flows

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities
Net loss	$ (103,102)	$ (85,407)	$ (50,010)
Adjustments to reconcile net loss to net cash (used in) operating activities:
Depreciation and amortization	1,764	1,643	1,430
Gain on disposal of equipment			(113)
Stock-based compensation	11,131	10,766	6,194
Changes in operating assets and liabilities:
Accounts receivable and other receivables	68,184	(70,657)	2
Income tax refund receivable		7,102	(7,102)
Prepaid and other current assets	782	(1,577)	(372)
Other assets	379	121	(781)
Deferred tax assets			10,331
Accounts payable	(1,770)	2,212	(1,323)
Accrued liabilities	(3,115)	3,662	(176)
Accrued clinical liabilities	9,633	5,392	3,864
Deferred revenue	(21,272)	52,284	(35,059)
Deferred rent	450	(679)	(624)
Income tax payable			(10,758)
Net cash used in operating activities	(36,936)	(75,138)	(84,497)
Investing activities
Purchases of property and equipment	(1,158)	(1,364)	(1,809)
Proceeds from sale of equipment			30
Purchases of short-term investments	(207,283)	(128,806)	(436,856)
Maturities of short-term investments	178,738	213,836	340,257
Net cash (used in) provided by investing activities	(29,703)	83,666	(98,378)
Financing activities
Proceeds from issuance of common stock related to the exercise of options and employee stock plan purchases	1,239	1,778	2,082
Net cash provided by financing activities	65,148	1,778	2,082
Net (decrease) increase in cash	(1,491)	10,306	(180,793)
Cash at beginning of year	38,444	28,138	208,931
Cash at end of year	36,953	$ 38,444	28,138
Supplemental cash flow information:
Accrued liabilities for purchase of property and equipment	301
Cash paid for income taxes, net			$ 8,200
At-the-Market Offering [Member]
Financing activities
Net proceeds from issuance of common stock	4,739
Public Offering [Member]
Financing activities
Net proceeds from issuance of common stock	$ 59,170

Organization

Organization	12 Months Ended
	Dec. 31, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization	1. Organization OncoMed Pharmaceuticals, Inc. (“OncoMed”, the “Company”, “us”, “we”, or “our”) is a clinical-stage biopharmaceutical company focused on discovering and developing novel therapeutics that address the fundamental biology driving cancer’s growth, resistance, recurrence and metastasis. The Company currently has eight therapeutic candidates in clinical development targeting cancer stem cell, or CSC, pathways and immuno-oncology, including its most recent Investigational New Drug, or IND, filing for its anti-TIGIT program. The Company plans to advance a ninth therapeutic candidate toward an IND application with the U.S. Food and Drug Administration, or FDA, in the first half of 2017. The Company is also pursuing discovery of additional novel approaches to cancer treatment, including new immuno-oncology therapeutic candidates. The Company was originally incorporated in July 2004 in Delaware. On July 17, 2013, the Company filed its registration statement on Form S-1 (File No. 333-181331) relating to the initial public offering of its common stock with the SEC and was closed on July 23, 2013. The Company’s operations are based in Redwood City, California and it operates in one segment.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The Company’s financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”). Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and judgments that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to revenue recognition, preclinical study and clinical trial accruals, fair value of assets and liabilities, income taxes, and stock-based compensation. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results may differ from those estimates. Cash and Cash Equivalents The Company considers all highly liquid investments with original maturities of 90 days or less at the date of purchase to be cash and cash equivalents. Short-Term Investments Short-term investments consist of debt securities classified as available-for-sale and have maturities greater than 90 days, but less than 365 days from the date of acquisition. Short-term investments are carried at fair value based upon quoted market prices. Unrealized gains and losses on available-for-sale securities are excluded from earnings and were reported as a component of accumulated other comprehensive income (loss). The cost of available-for-sale securities sold is based on the specific-identification method. Concentrations of Credit Risk Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash and short-term investments. Cash and short-term investments are invested through banks and other financial institutions in the United States. Such deposits may be in excess of insured limits. The Company maintains cash and investments with various high credit quality and capitalized financial institutions. Property and Equipment Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization is calculated using the straight-line method over the estimated useful lives of the assets, which range from three to five years. Leasehold improvements are amortized over the shorter of their estimated useful lives or the remaining life of the lease at the time the asset is placed into service. Impairment of Long-Lived Assets The carrying value of long-lived assets, including property and equipment, are reviewed for impairment whenever events or changes in circumstances indicate that the asset may not be recoverable. An impairment loss is recognized when the total of estimated future undiscounted cash flows, expected to result from the use of the asset and its eventual disposition, are less than its carrying amount. Impairment, if any, would be assessed using discounted cash flows or other appropriate measures of fair value. Through December 31, 2016, there have been no such impairment losses. Revenue Recognition The Company generates substantially all its revenue from collaborative research and development agreements with pharmaceutical companies. The terms of the agreements may include nonrefundable upfront payments, milestone payments, other contingent payments and royalties on any product sales derived from collaborations. These multiple element arrangements are analyzed to determine whether the deliverables can be separated or whether they must be accounted for as a single unit of accounting. The determination of stand-alone value is generally based on whether any deliverable has stand-alone value to the customer. The Company determines how to allocate arrangement consideration to identified units of accounting based on the selling price hierarchy provided under the relevant guidance. The selling price used for each unit of accounting is based on vendor-specific objective evidence, if available, third-party evidence if vendor-specific objective evidence is not available or estimated selling price if neither vendor-specific nor third-party evidence is available. Management may be required to exercise considerable judgment in determining whether a deliverable is a separate unit of accounting and in estimating the selling prices of identified units of accounting for new agreements. Typically, the Company has not granted licenses to collaborators at the beginning of its arrangements and thus there are no delivered items separate from the research and development services provided. As such, upfront payments are recorded as deferred revenue in the balance sheet and are recognized as collaboration revenue over the estimated period of performance that is consistent with the terms of the research and development obligations contained in the collaboration agreement. The Company regularly reviews the estimated period of performance based on the progress made under each arrangement. Payments that are contingent upon achievement of a substantive milestone are recognized in their entirety in the period in which the milestone is achieved. Milestones are defined as an event that can only be achieved based on the Company’s performance and there is substantive uncertainty about whether the event will be achieved at the inception of the arrangement. Events that are contingent only on the passage of time or only on counterparty performance are not considered milestones. Further, the amounts received must relate solely to prior performance, be reasonable relative to all of the deliverables and payment terms within the agreement and commensurate with the Company’s performance to achieve the milestone after commencement of the agreement. Other contingent payments received for which payment is contingent solely on the results of a collaborative partner’s performance (bonus payments) are not accounted for using the milestone method. Such bonus payments will be recognized as revenue when collectability is reasonably assured. Amounts received prior to satisfying the revenue recognition criteria are recorded as deferred revenue in the Company’s balance sheets. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as current liabilities. The Company recognizes revenue for reimbursements of research and development costs under collaboration agreements as the services are performed. The Company records these reimbursements as revenue on a gross basis and not as a reduction of research and development expenses, as the Company has the risks and rewards as the principal in the research and development activities. Payments related to options to license the Company’s program candidates are considered substantive if, at the inception of the arrangement, the Company is at risk as to whether the collaboration partner will choose to exercise the option. Factors that the Company considers in evaluating whether an option is substantive include the overall objective of the arrangement, the benefit the collaborator might obtain from the arrangement without exercising the option, the cost to exercise the option and the likelihood that the option will be exercised. For arrangements under which an option is considered substantive, the Company does not consider the item underlying the option to be a deliverable at the inception of the arrangement and the associated opt-in payments are not included in allocable arrangement consideration, assuming the option is not priced at a significant and incremental discount. Conversely, for arrangements under which an option is not considered substantive or if an option is priced at a significant and incremental discount, the Company would consider the item underlying the option to be a deliverable at the inception of the arrangement and a corresponding amount would be included in allocable arrangement consideration. Customer Concentration Customers whose collaboration revenue accounted for 10% or more of total revenues were as follows: Year Ended December 31, 2016 2015 2014 GlaxoSmithKline LLC (“GSK”) * 25% 31% Bayer Pharma AG (“Bayer”) * 14% 30% Celgene Corporation (“Celgene”) 87% 61% 39% * less than 10% Research and Development Expenses Research and development costs are expensed as incurred. Research and development costs consist of salaries and other personnel-related expenses, including associated stock-based compensation, consulting fees, lab supplies, and facility costs, as well as fees paid to other entities that conduct certain research, development and manufacturing activities on behalf of the Company. Clinical Trial Accruals Clinical trial costs are a component of research and development expenses. The Company accrues and expenses clinical trial activities performed by third parties based upon actual work completed in accordance with agreements established with clinical research organizations and clinical sites. The Company determines the actual costs through discussions with internal personnel and external service providers as to the progress or stage of completion of trials or services and the agreed-upon fee to be paid for such services. Nonrefundable advance payments for goods and services that will be used or rendered in future research and development activities, are deferred and recognized as expense in the period that the related goods are delivered or services are performed. Stock-Based Compensation The Company recognizes compensation expense for all share-based payment awards made to employees and directors based on estimated fair values. For employee stock options, the Company determines the grant date fair value of the awards using the Black-Scholes option-pricing model and generally recognizes the fair value as stock-based compensation expense on a straight-line basis over the vesting period of the respective awards. Stock-based compensation expense is based on the value of the portion of stock-based payment awards that is ultimately expected to vest. As such, the Company’s stock-based compensation is reduced for the estimated forfeitures at the date of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. For restricted stock, the compensation cost for these awards is based on the closing price of the Company’s common stock on the date of grant and recognized as compensation expense on a straight-line basis over the requisite service period. The Company accounts for equity instruments issued to nonemployees based on their fair values on the measurement dates using the Black-Scholes option-pricing model. The estimated fair values of the options granted to nonemployees are remeasured as they vest. As a result, the noncash charge to operations for nonemployee options with vesting conditions is affected each reporting period by changes in the fair value of the Company’s common stock. Leases The Company rents its office space and facilities under cancelable and non-cancelable operating lease agreements and recognizes related rent expense on a straight-line basis over the term of the lease. The Company’s lease agreements contain rent holidays, scheduled rent increases, lease incentives and renewal options. Rent holidays and scheduled rent increases are included in the determination of rent expense to be recorded over the lease term. Lease incentives are recognized as a reduction of rent expense on a straight-line basis over the term of the lease. The Company does not assume renewals in its determination of the lease term unless they are deemed to be reasonably assured at the inception of the lease. The Company begins recognizing rent expense on the date that the Company obtains the legal right to use and control the leased space. Income Taxes The Company accounts for income taxes using the liability method under which deferred tax assets and liabilities are determined based on differences between financial reporting and tax basis of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. Valuation allowances are established when necessary to reduce deferred tax assets to the amount which is more likely than not to be realizable. The recognition, derecognition and measurement of a tax position is based on management’s best judgment given the facts, circumstances and information available at each reporting date. The Company’s policy is to recognize interest and penalties related to the underpayment of income taxes as a component of income tax expense. To date, there have been no interest or penalties charged in relation to the unrecognized tax benefits. Net Loss per Common Share Basic net loss per common share is calculated by dividing the net loss by the weighted-average number of common shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per common share is computed by dividing the net loss by the weighted-average number of common shares and common share equivalents outstanding for the period determined using the treasury-stock method. For purposes of this calculation, potentially dilutive securities consisting of stock options and restricted stock units are considered to be common stock equivalents and were excluded in the calculation of diluted net loss per common share because their effect would be anti-dilutive for all periods presented. Newly Adopted and Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, 2014-09, Revenue from Contracts with Customers: Topic 606 In March, April, May and December 2016, the FASB issued ASU 2016-08, Revenue from Contracts with Customers: Principal versus Agent Considerations , ASU 2016-10, Revenue from Contracts with Customers: Identifying Performance Obligations and Licensing , ASU 2016-12, Revenue from Contracts with Customers: Narrow-Scope Improvements and Practical Expedients to provide supplemental adoption guidance and clarification to ASU 2014-09 and ASU 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers , respectively. The effective date for these new standards is the same as the effective date and transition requirements for ASU 2014-09. The Company expects to adopt ASU 2014-09 in the first quarter of 2018 using the modified retrospective method. The adoption of ASU 2014-09 may have a material effect on the Company’s financial statements. To date, we have derived our revenues collaboration agreements. The consideration the Company is eligible to receive under these agreements includes upfront payments, research and development funding, and milestone payments. Each collaboration agreement is unique and will need to be assessed separately under the five-step process under the new standard. The Company has started its preliminary assessment of our active license and collaboration agreements. The Company expects that its evaluation of the accounting for collaboration agreements under the new revenue standard could identify material changes from the current accounting treatment. ASU 2014-09 differs from the current accounting standard in many respects, such as in the accounting for variable consideration, including milestone payments. Under our current accounting policy, the Company recognizes milestone revenue using the milestone method specified in ASC 605-28, which generally results in the recognition of the milestone payment as revenue in the period that the milestone is achieved. However, under the new accounting standard, it is possible to start to recognize milestone revenue before the milestone is achieved, subject to management’s assessment of whether it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. In addition, the current accounting standards include a presumption that revenue from up-front non-refundable fees would be recognized ratably over the performance period, unless another attribution method was determined to more closely approximate the delivery of the goods or services to the customer. The new accounting standard does not have a presumption that entities would default to a ratable attribution approach and will require entities to determine an appropriate attribution method using either output or input methods. As such, the amount and timing of revenue recognition for the Company’s collaboration agreements may change under the new revenue standard. In August 2014, the FASB issued ASU No. 2014-15 (Subtopic 205-40) “Presentation of Financial Statements—Going Concern: Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern.” ASU 2014-15 provides guidance about management’s responsibility to evaluate whether or not there is substantial doubt about the Company’s ability to continue as a going concern and to provide related footnote disclosure. ASU 2014-15 is effective for fiscal years ending after December 15, 2016, and for interim and annual periods therein, with early adoption permitted. The Company adopted this guidance in the fourth quarter of 2016. The adoption of the standard did not have material impact on the Company’s financial statements. In February 2016, the FASB issued ASU 2016-02 “Leases.” ASU 2016-02 amends a number of aspects of lease accounting In March 2016, the FASB issued ASU 2016-09 “Improvements to Employee Share-Based Payment Accounting.” ASU 2016-09 simplifies several aspects of employee share-based payment accounting, including the income tax consequences, classification of awards as either equity or liabilities and classification on the statement of cash flows. This guidance will become effective for the Company beginning in the first quarter of 2017, with early adoption permitted. The Company plans to adopt the guidance in the first quarter of 2017. The Company is evaluating the impact of the adoption of this standard on its financial statements.

Cash and Investments

Cash and Investments	12 Months Ended
	Dec. 31, 2016
Cash And Cash Equivalents [Abstract]
Cash and Investments	3. Cash and Investments The fair value of securities, not including cash at December 31, 2016 and 2015 were as follows (in thousands): December 31, 2016 Amortized Gross Unrealized Fair Cost Gains Losses Value U.S. treasury bills $ 147,360 $ 260 $ — $ 147,620 Total $ 147,360 $ 260 $ — $ 147,620 Classified as: Short-term investments $ 147,620 As of December 31, 2016, the Company had a total of $184.6 million in cash and short-term investments, which includes $37.0 million in cash and $147.6 million in short-term investments. December 31, 2015 Amortized Gross Unrealized Fair Cost Gains Losses Value U.S. treasury bills $ 118,815 $ 40 $ (20 ) $ 118,835 Total $ 118,815 $ 40 $ (20 ) $ 118,835 Classified as: Short-term investments $ 118,835 As of December 31, 2015, the Company had a total of $157.3 million in cash and short-term investments, which includes $38.5 million in cash and $118.8 million in short-term investments. All available-for-sale securities held as of December 31, 2016 and 2015 had contractual maturities of less than one year. There have been no significant realized gains or losses on available-for-sale securities for the periods presented.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Fair Value Measurements	4. Fair Value Measurements The Company records its financial assets and liabilities at fair value. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the reporting date. The accounting guidance establishes a three-tiered hierarchy, which prioritizes the inputs used in the valuation methodologies in measuring fair value as follows: • Level 1: Inputs which include quoted prices in active markets for identical assets and liabilities. • Level 2: Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. • Level 3: Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. The Company’s financial assets and liabilities subject to fair value measurements on a recurring basis and the level of inputs used in such measurements were as follows (in thousands): December 31, 2016 Level 1 Level 2 Level 3 Total Assets: U.S. treasury bills $ — $ 147,620 $ — $ 147,620 Total $ — $ 147,620 $ — $ 147,620 December 31, 2015 Level 1 Level 2 Level 3 Total Assets: U.S. treasury bills $ — $ 118,835 $ — $ 118,835 Total $ — $ 118,835 $ — $ 118,835 Where quoted prices are available in an active market, securities are classified as Level 1. When quoted market prices are not available for the specific security, then the Company estimates fair value by using benchmark yields, reported trades, broker/dealer quotes, and issuer spreads. The Company classifies U.S. Treasury securities as Level 2. There were no transfers between Level 1 and Level 2 during the periods presented.

Property and Equipment, net

Property and Equipment, net	12 Months Ended
	Dec. 31, 2016
Property Plant And Equipment [Abstract]
Property and Equipment, net	5. Property and Equipment, net Property and equipment, net consist of the following (in thousands): December 31, 2016 2015 Computer equipment and software $ 1,897 $ 1,828 Furniture and fixtures 527 498 Laboratory equipment 11,452 10,286 Leasehold improvements 9,095 9,064 22,971 21,676 Less accumulated depreciation and amortization (18,500 ) (16,851 ) Property equipment, net $ 4,471 $ 4,825 Depreciation expense for the years ended December 31, 2016, 2015 and 2014 was $1.8 million, $1.6 million and $1.4 million, respectively.

Accrued Liabilities

Accrued Liabilities	12 Months Ended
	Dec. 31, 2016
Payables And Accruals [Abstract]
Accrued Liabilities	6. Accrued Liabilities Accrued liabilities consist of the following (in thousands): December 31, 2016 2015 Research and development related $ 3,143 $ 4,941 Compensation related 4,922 6,019 Other 534 515 Total accrued liabilities $ 8,599 $ 11,475

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2016
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	7. Commitments and Contingencies Operating Leases The Company leases office and laboratory facilities in Redwood City, California under a lease agreement that expires in January 2019 and includes a lease extension option for two additional three-year terms. During the fourth quarter of 2016, the Company signed an amendment to the lease agreement to extend the lease term through May 2028 with an option to extend the lease for additional three-year term. The amendment to the lease agreement includes a 10-year cancelable lease agreement for additional office and laboratory space that expires in May 2028, subject to the Company’s three-year lease extension option described above. The base rent obligation on this additional space is estimated to commence in June 2018 and the total estimated base rent payments over the life of the lease are approximately $13.8 million. In addition to the base rent payments, the Company will be obligated to pay certain customary amounts for the Company’s share of operating expenses and tax obligations. The Company has the right to terminate the lease agreement for this additional space prior to September 16, 2017 and the exercise of such cancelation would not result in an economic penalty to the Company. As of December 31, 2016, minimum annual rental payments under the Company’s non-cancelable operating lease agreement are as follows (in thousands): Year ending December 31, 2017 $ 1,707 2018 2,323 2019 2,406 2020 2,490 2021 and thereafter 21,387 Total minimum payments $ 30,313 In prior years, the landlord provided the Company a tenant improvement allowance for a total of $7.3 million to complete the office and laboratory expansion. The Company recorded the tenant improvement allowance received as leasehold improvements under the property and equipment account and deferred rent liability on the accompanying balance sheets. The operating lease agreement contains rent escalation provisions and tenant improvement allowances. The total rent obligation is being expensed ratably over the term of the agreement. Rent expense for years ended December 31, 2016, 2015 and 2014, was $1.6 million, $1.3 million and $1.3 million, respectively. Guarantees and Indemnifications The Company, as permitted under Delaware law and in accordance with its certificate of incorporation and bylaws, and pursuant to indemnification agreements with certain of its officers and directors, indemnifies its officers and directors for certain events or occurrences, subject to certain limits, while the officer or director is or was serving at the Company’s request in such capacity. The term of the indemnification period lasts as long as an officer or director may be subject to any proceeding arising out of acts or omissions of such officer or director in such capacity. The maximum amount of potential future indemnification is unlimited; however, the Company currently holds director and officer liability insurance. This insurance limits the Company’s exposure and may enable it to recover a portion of any future amounts paid. The Company believes that the fair value of these indemnification obligations is minimal. Accordingly, the Company has not recognized any liabilities relating to these obligations for any period presented.

License Agreement

License Agreement	12 Months Ended
	Dec. 31, 2016
Research And Development [Abstract]
License Agreement	8. License Agreement In 2004, the Company assumed an exclusive, worldwide license agreement with the University of Michigan relating to the use of certain patents and technology relating to its CSC technology for which an up-front fee of $10,000 had been paid and the Company issued 7,796 shares of its common stock. Pursuant to the agreement, the Company is obligated to make low single-digit royalty payments to the University of Michigan on net sales of its or its licensees products and processes covered under the agreement, pay an annual license maintenance fee, and reimburse the University of Michigan for costs of prosecution and maintenance of the licensed patents which reduces future royalty obligations. With respect to one family of licensed patent applications that does not relate to any of the Company’s lead therapeutic programs, the Company is also required to pay a tiered, single-digit percentage of any sublicense revenues, including any upfront or milestone payments, received from any sublicensees under such family of patents. Once the University of Michigan has received $10.0 million in royalties, the Company may at its option convert the license to a fully paid-up license provided the Company transfers additional shares of nonvoting common stock equal to 0.25% of the fully diluted shares then outstanding to the University of Michigan. The amounts incurred for patent legal costs amounted to $69,000, $65,000 and $158,000 for the years ended December 31, 2016, 2015 and 2014, respectively, all of which has been recorded as general and administrative expense in the statements of operations.

Supply and License Agreements

Supply and License Agreements	12 Months Ended
	Dec. 31, 2016
Research And Development [Abstract]
Supply and License Agreements	9. Supply and License Agreements In June 2006, the Company entered into a subscription and license agreement with MorphoSys AG to obtain a research license and access to certain technology libraries, antibodies and support services. The Company paid technology access and subscription fees from the date of signing through 2008 of €650,000 (approximately $919,000) and €250,000 (approximately $350,000) in 2009. The Company obtained from MorphoSys AG an extended research license that may be renewed by the Company on an annual basis through 2020, subject to an annual fee of €20,000 (approximately $22,000). Additionally, the Company may owe MorphoSys AG up to €5.8 million (approximately $6.3 million) in future milestone payments for each product developed using the licensed antibodies if all milestone events are achieved, primarily in Phase III clinical trials and later development. GSK would reimburse the Company for 50% of such payments for tarextumab (Anti-Notch2/3, OMP-59R5) under the MorphoSys agreement, and we have received a total of $992,000 from GSK in such reimbursements through December 31, 2016. In April/May 2008, the Company obtained commercial licenses to two antibodies identified from the licensor’s library of antibodies, and must make additional payments to MorphoSys AG for these licenses. GSK reimburses the Company for 50% of the license payments for the first antibody, which is used in the tarextumab program under the Company’s collaboration with GSK, while the Company is responsible for all the license payments for the second antibody, which is used in the vantictumab (anti-Fzd, OMP-18R5) program under its collaboration with Bayer. There were no payments made for the licensed antibodies nor reimbursements received from GSK during the years ended December 31, 2016, 2015 and 2014.

Collaborations

Collaborations	12 Months Ended
	Dec. 31, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaborations	10. Collaborations The Company has entered into three collaboration arrangements, each having multiple deliverables under which it received non-refundable upfront payments. For collaborations where the Company has determined that there is a single unit of accounting the Company recognizes revenue related to the upfront payments ratably over its estimated period of performance for each collaboration. The Company has entered into collaborations arrangements that include contractual milestones, which relate to the achievement of pre-specified research, development, regulatory and commercialization events. The milestone events contained in the Company’s alliances coincide with the progression of the Company’s product candidates from research and development, to regulatory approval and through to commercialization. The process of successfully discovering a new product candidate, having it selected by the alliance partner for development, having it approved and ultimately sold for a profit is highly uncertain. As such, the milestone payments that the Company may earn from its collaborators involve a significant degree of risk to achieve. Research and development milestones in the Company’s strategic alliances may include the following types of events: • Completion of pre-clinical research and development work leading to selection of product clinical candidates. • Advancement of candidates into clinical development, which may include filing of investigational new drug (“IND”) applications. • Initiation of Phase I, Phase II or Phase III clinical trials. • Achievement of certain scientific or development events. Regulatory milestones may include the following types of events: • Filing of regulatory applications for marketing approval such as a New Drug Application in the United States, or a Marketing Authorization Application in Europe. • Marketing approval in a major market, such as the United States, Europe or Japan. Commercialization milestones may include the following types of events: • Product sales in excess of pre-specified thresholds. Summary of Collaboration Related Revenue The Company has recognized the following revenues from its collaboration agreements during the years ended December 31, 2016, 2015 and 2014 (in thousands): Year Ended December 31, 2016 2015 2014 GSK: Recognition of upfront payment $ 576 $ 1,123 $ 1,248 Milestone revenue — 5,000 11,000 Other revenue 639 363 — GSK total 1,215 6,486 12,248 Bayer: Recognition of upfront payments 648 3,518 9,756 Milestone revenue — — 2,000 Other revenue 1,457 — — Bayer total 2,105 3,518 11,756 Celgene: Recognition of upfront payment 20,053 13,055 13,055 Milestone revenue — 2,520 2,500 Other revenue 1,780 320 — Celgene total 21,833 15,895 15,555 Total collaboration related revenue $ 25,153 $ 25,899 $ 39,559 GSK Strategic Alliance On December 7, 2007, the Company entered into a Collaboration and Option Agreement with GSK. The agreement was formed to discover, develop and market novel antibody therapeutics to target CSCs. The agreement gives GSK the option to obtain an exclusive license for certain product candidates targeting the Notch signaling pathway. Under the original agreement, the Company had a research obligation to provide GSK four antibodies that meet specified selection criteria and was responsible for the development of two antibodies through clinical proof-of-concept, or POC, generally considered to be at the end of certain Phase II clinical trials. There is no further obligation by the Company to perform development once these are achieved. Upon exercise of its option, GSK obtains an exclusive worldwide license to the antibody, assumes full financial responsibility for funding further clinical development and commercialization and will be obligated to make payments to the Company for further development and commercialization milestones and royalties on product sales. The Company received an initial payment of $35.0 million, with half in the form of an equity investment by GSK in the Company’s Series B-2 convertible preferred stock and the other half as an up-front cash payment which was initially recorded as deferred revenue. The Company is eligible to earn milestone payments in connection with research and development activities, and contingent consideration in connection with further development, regulatory approval and commercialization activities. In addition, the Company can earn royalty payments on all future collaboration product sales, if any. The 1,441,396 shares of Series B-2 convertible preferred stock sold by the Company to GSK were issued at a premium of $4.3 million above the estimated fair value of convertible preferred stock at the time of issuance. This premium was considered an additional up-front payment and was added to the $17.5 million deferred revenue and was being recognized on a ratable basis over the estimated period of performance of five years. In July 2011, the Company amended the terms of its development agreement with GSK to focus the collaboration entirely on the development of two product candidates, tarextumab (anti-Notch2/3, OMP-59R5) and brontictuzumab (anti-Notch1, OMP-52M51). The Company was entitled to receive additional funding from GSK to support certain of its development activities conducted in relation to one of these product candidates, up to a maximum of $2.0 million. The Company evaluated the terms of the July 2011 amendment relative to the entire arrangement and determined the amendment to be a material modification to the original agreement for financial reporting purposes. As a result, the Company evaluated the entire arrangement under the multiple-element accounting guidance. The Company determined that the only undelivered elements were providing certain development services it is obligated to provide for the second product candidate and the continued development work to progress the first product candidate through certain Phase II POC clinical trials. The Company has determined that the undelivered elements are a single unit of accounting. Accordingly, the $7.9 million deferred revenue balance at the modification date was being recognized as revenue ratably over the estimated period of performance over four years beginning on the date of the material modification of the original agreement. The Company determined that the clinical data it has obtained to date supported a change in study design which extended the estimated completion of the deliverable, certain Phase II POC clinical trials to June 2016. In January 2014, the Company changed its estimate of the period of performance from four years to five years. Accordingly, the Company is recognizing the remaining unamortized portion of the up-front payment over the revised estimated period of performance on a prospective basis. In July 2012, the Company and GSK entered into the Second Amendment Regarding Payment of Certain Milestone Payments for the tarextumab program. This amendment modified one of the development milestones for advancing the tarextumab program. The restructuring of the milestone payment did not alter the aggregate amount of development milestone payments or the aggregate amount of contingent consideration payments that the Company is eligible to receive in its collaboration with GSK. The Company received a $3.0 million payment upon the initiation of the Phase Ib portion of the tarextumab program in October 2012, which was not considered to be the achievement of a substantive milestone for accounting purposes. Rather it is an advance payment on a future substantive milestone. Accordingly, the $3.0 million was recorded as deferred revenue to be recognized upon the achievement of the underlying substantive milestone. This modification was not material to the collaboration taken as a whole. During the year ended December 31, 2012, the Company recognized a $5.0 million proof-of-principle development milestone for the tarextumab program, a $5.0 million development milestone for the IND acceptance for its brontictuzumab program and a $4.0 million development milestone for the first patient enrollment for its brontictuzumab clinical trial. In June 2013, the Company received an $8.0 million advance payment from GSK pursuant to the terms of its tarextumab program. The $8.0 million was recorded as deferred revenue to be recognized as collaboration revenue upon the achievement of the underlying substantive milestone. In July 2014, the Company began dosing patients in the randomized, placebo-controlled Phase II portion of its clinical trial of tarextumab in pancreatic cancer. As a result, payments of $8.0 million and $3.0 million previously recorded as deferred revenue were recognized as collaboration revenue upon the achievement of this underlying substantive milestone. In January 2015, the Company enrolled the first biomarker-selected patient in the expansion stage of the brontictuzumab (anti-Notch1, OMP-52M51) Phase Ia trial in solid tumors. The advancement to the predictive biomarker expansion stage triggered a $5.0 million substantive milestone payment from GSK, which the Company recognized as collaboration revenue in 2015. In addition, the Company recognized $0.4 million revenue for the reimbursement of research and development costs for services performed in 2015. On October 31, 2016, GSK provided written notice to the Company that it was terminating its option to obtain an exclusive license to develop and commercialize brontictuzumab. After such termination became effective on January 29, 2017, the Company retained worldwide rights to brontictuzumab. Under certain circumstances, the Company may owe GSK single-digit percentage royalties on net product sales of brontictuzumab, subject to a cap. The Company revised the estimated periods of performance and extended the amortization of the upfront payment to March 2017, which caused a $0.1 million decrease in revenue in 2016. As of December 31, 2016, the Company was eligible to receive in its collaboration with GSK with respect to tarextumab $319.5 million in future development milestone payments and contingent consideration, including a $25.0 million opt-in payment and development, regulatory and commercialization payments in addition to percentage royalties in the low double digits to high teens on net product sales. The Company has earned $25.0 million in the aggregate from GSK with respect to tarextumab through December 31, 2016. If GSK elects not to exercise its option for tarextumab during its option period, or if GSK terminates the tarextumab program, the Company will have worldwide rights to such program. Bayer Strategic Alliance On June 15, 2010, the Company entered into a Collaboration and Option Agreement with Bayer. The agreement sets forth an alliance to discover, develop and market novel antibody, protein and small molecule therapeutics targeting CSCs. Specifically, the alliance efforts are directed toward therapeutics affecting targets within the Wnt signaling pathway. Under the terms of the agreement, Bayer has an exclusive option to license biologic therapeutic product candidates discovered and developed by the Company over a biologics research term that will extend until the later of five years after the effective date of the agreement or the occurrence of certain specified events. In addition, the Company will assist Bayer with its advancement of a specified number of small molecule candidates discovered and developed at Bayer to certain development stages. The Company estimates its period of performance to be approximately five years. The Company is obligated to use commercially reasonable efforts to advance three biologics through to a specified stage of research and two biologics to a specified early clinical development stage. The option for Bayer to obtain an exclusive license to any of the biologics therapeutic product candidates commences on the effective date of the agreement and extends for a specified time period. The Company is responsible for all preclinical and development costs for each biologic product candidate up to the end of a defined early clinical development stage. Once Bayer exercises its option to obtain an exclusive license to a class of biologic therapeutic products, it assumes full financial responsibility for funding further clinical development and commercialization of such product candidates. The Company received an upfront payment of $40.0 million and is eligible to receive aggregate development, regulatory approval and commercialization milestone or post-opt-in contingent consideration payments up to $387.5 million for each biologic and $112.0 million for each small molecule candidate. The upfront payment was recorded as deferred revenue and is being amortized to revenue over the Company’s estimated period of performance. Upon product sales, the Company is eligible to receive royalties that adjust depending on sales volume. The Company achieved a $20.0 million development milestone related to the acceptance of the IND for the vantictumab (anti-Fzd, OMP-18R5) product candidate during the year ended December 31, 2011 that was determined to be substantive and at risk at the inception of the arrangement and, as such, was recognized in the period the milestone was achieved. In April 2011, the Company entered into a clinical manufacturing agreement which expanded its alliance with Bayer. Pursuant to this agreement, Bayer HealthCare LLC agreed to manufacture ipafricept (Fzd8-Fc, OMP-54F28) at its Berkeley, California site to support the Company’s clinical development activities. In August 2012, the Company and Bayer entered into Amendment 1 to the Collaboration and Option Agreement. This amendment modified the timing of payments under the Company’s ipafricept program and another biologic therapeutic product program under the agreement. The modification did not alter the aggregate amount of development milestone payments or the aggregate amount of contingent consideration payments the Company is eligible to receive in its collaboration with Bayer. This modification was not material to the collaboration taken as a whole. During the year ended December 31, 2012, the Company received a $5.0 million payment related to the ipafricept program. As the payment was not deemed to be for a substantive milestone under Amendment 1, the Company is recognizing the $5.0 million payment over the remaining estimated period of performance under the agreement. In August 2013, the Company and Bayer entered into Amendment 2 to the Collaboration and Option Agreement. The amendment confirms the achievement of a development milestone of $10.0 million for dose escalation of vantictumab in Phase Ia as well as agreement on the Phase Ib trial design. In addition, the amendment excludes a target that is not being developed under the collaboration. This amendment was not considered a material modification for accounting or reporting purposes. In October 2013, the Company achieved a $15.0 million development milestone related to Phase I dose escalation in its ipafricept program under its agreement with Bayer. The two milestones totaling $25.0 million were determined to be substantive and at risk at the inception of the agreement and, as such, were recognized in the period the milestones were achieved. In September 2014, the Company earned $2.0 million in milestone payments from Bayer as a result of the commencement of preclinical development of a small molecule product candidate. The $2.0 million milestone was determined to be substantive and at risk at the inception of the agreement and, as such, was recognized in the period the milestone was achieved. In November 2015, the Company further amended its agreement with Bayer to allow the Company the right to add, in its sole discretion, an additional dose escalation cohort of six patients to each of its Phase Ib trial of vantictumab in combination with standard-of-care therapy in breast cancer and its Phase Ib trial of ipafricept in combination with standard-of-care therapies in ovarian cancer. In addition, the Company agreed with Bayer to add six additional patients to the expansion cohort of each of these Phase Ib trials. The Company revised the estimated periods of performance and extended the amortization of the upfront payment to June 2017, which caused a $0.1 million decrease in revenue in 2016. As of December 31, 2016, the Company was eligible to receive up to $10.0 million in future development milestone payments in its collaboration with Bayer for the Company’s development of biologic product candidates, prior to the point that Bayer exercises its options. The Company is eligible to receive up to $55.0 million if Bayer exercises its options for biologic product candidates. Bayer will be responsible for all further development and commercialization following the exercise of an option for a product candidate. The Company is eligible to receive up to $22.0 million in development milestone payments for the small molecule candidates. If Bayer successfully develops and commercializes all of the product candidates for more than one indication, the Company could receive contingent consideration payments of up to $185.0 million for the achievement of regulatory events (up to $135.0 million for biologics and $50.0 million for small molecules) and up to $1.0 billion upon the achievement of specified future product sales (up to $862.5 million for biologics and $140.0 million for small molecules). As all contingent consideration is based solely on the performance of Bayer, the Company would recognize the contingent payments upon receipt immediately as collaboration revenue if the Company had no further performance obligations under the agreement with Bayer. Celgene Strategic Alliance In December 2013, the Company entered into a Master Research and Collaboration Agreement (the Agreement) with Celgene pursuant to which the Company and Celgene will collaborate on research and development programs directed to the discovery and development of novel biologic therapeutic programs to target CSCs, and, if Celgene exercises an option to do so, the discovery, development and commercialization of novel small molecule therapeutic programs to target CSCs. Pursuant to the biologic therapeutic programs, the Company will conduct further development of demcizumab, navicixizumab, biologic therapeutics directed to targets in the RSPO-LGR signaling pathway, including anti-RSPO3 (OMP-131R10), and biologic therapeutics directed to targets in an undisclosed pathway. Celgene has options to obtain exclusive licenses to develop further and commercialize biologic therapeutics in specified programs, which may be exercised during time periods specified in the agreement through the earlier of completion of certain clinical trials or the twelfth anniversary of the date of the Agreement. The Company at its option may enter into co-commercialization and co-development agreements for five of the six biologic programs. Prior to the expiration of Celgene’s options under the Agreement, the Company will provide research and development services and the resultant data to Celgene for analysis in order for Celgene to determine whether or not to exercise its options. Pursuant to the Agreement, the Company leads the discovery and development of each biologic therapeutic product prior to Celgene’s exercise of its option for the applicable program. With respect to biologic therapeutics targeting the RSPO-LGR signaling pathway and the undisclosed pathway, prior to Celgene’s exercise of its option for a given program, Celgene is required to designate each program for which it wishes to retain the right to exercise its option, based on data generated by the Company, for up to a maximum of four programs. The Company is entitled to receive certain fees for each program that Celgene designates. Celgene has the right to designate programs until December 2, 2017, with an option to extend for another two years upon payment of an extension fee. Following such designation(s), Celgene will have the right to exercise its option for each such program through the earlier of completion of certain clinical trials or the twelfth anniversary of the date of the Agreement. With respect to biologic therapeutic programs, with the exception of one program targeting either the RSPO-LGR signaling pathway or the undisclosed pathway, and any program for which the Company elects not to exercise its co-development and co-commercialization right, following Celgene’s exercise of its option, the Company and Celgene will enter into an agreed form of co-development and co-commercialization agreement for such program. The Company will have the right to co-develop and to co-commercialize products arising out of such program in the United States, and Celgene will have the exclusive right to develop and commercialize products arising out of such program outside of the United States. The Company’s involvement in co-commercialization will include participation in specified promotion activities by means of a dedicated sales force of up to half of the overall sales force for the applicable program products, as well as marketing and other commercial activities, with Celgene recording all product sales. The Company will also bear a one-third share of all development costs, with Celgene bearing the remaining two-thirds. However, for one program targeting either the RSPO-LGR signaling pathway or the undisclosed pathway, and any program for which the Company elects not to co-develop and co-commercialize products arising from such program, the Company and Celgene will instead enter into an agreed form of a license agreement, pursuant to which Celgene retains all rights to develop further and commercialize biologic therapeutic products arising from such program on a worldwide basis, with certain support for development from the Company. The Company may elect not to co-develop and co-commercialize any products arising under such programs at any time, either prior to, or following Celgene’s option exercise, with the exception of a defined period of time near commercial launch of a product under a program. If the Company opts out of its co-development and co-commercialization rights with respect to a program, Celgene will have the exclusive right to develop and commercialize products arising out of such program, at Celgene’s expense. With respect to small molecule therapeutics targeting an undisclosed pathway, following Celgene’s exercise of its option, the Company will collaborate with Celgene on the discovery of and research on small molecule therapeutics, but Celgene will be solely responsible for development and commercialization of such therapeutics. Under the terms of the Agreement, the Company received an upfront cash payment of $155.0 million. In addition, Celgene purchased 1,470,588 shares of the Company’s common stock at a price of $15.13 per share, resulting in gross proceeds of $22.2 million. The price paid by Celgene for the common stock represented a premium over the closing price of the Company’s common stock on the date of the Agreement. The Company accounted for the $1.7 million premium as additional consideration under the Agreement and the common stock was recorded at its fair market value of $20.5 million. The Company is also eligible to receive opt-in payments upon Celgene’s exercise of the option for each biologic therapeutic program. The collaboration also includes milestone payments for achievement of specified development, regulatory and commercial milestones, paid on a per-product and per-program basis. The payments for option exercise, program designation and achievement of development, regulatory and commercial milestones may total up to (1) $791.0 million for products in the demcizumab program, including a $70.0 million opt-in payment, (2) $505.0 million for products in the navicixizumab program, including a $25.0 million opt-in payment, (3) approximately $442.8 million for products in the anti-RSPO3 program, including an approximately $37.8 million opt-in payment, (4) $440.0 million for products in the anti-TIGIT program, including a $35.0 million opt-in payment, (5) $440.0 million for each of up to two additional biologic programs achieving regulatory approval that are directed to targets in either the RSPO-LGR signaling pathway and the undisclosed pathway for which Celgene exercises its option, and (6) $107.0 million for products in the small molecule therapeutic program. For programs in which the Company is co-developing and co-commercializing biologic therapeutic products in the United States, the Company is also entitled to share 50% of all product profits and losses in the United States. For such programs outside the United States, the Company is eligible to receive tiered royalties equal to a percentage of net product sales outside of the United States. If the Company elects not to co-develop or co-commercialize biologic therapeutic products or does not have the right to do so for a given program, Celgene is required to pay the Company tiered royalties equal to a percentage of net product sales worldwide, with such royalties being increased where the Company had the right to co-develop and co-commercialize such biologic therapeutic products under such program but elected not to do so. The Company is responsible for funding all research and development activities for biologic therapeutics under the collaboration prior to Celgene’s exercise of the option for such program. In addition to the development and regulatory milestone payments the Company will be entitled to receive if Celgene exercises its option for the small molecule program, the Company may also receive royalties equal to a percentage of worldwide net sales of small molecule products in the low- to mid-single digits. The Agreement will terminate upon the expiration of all of Celgene’s payment obligations under all license or co-development and co-commercialization agreements entered into with respect to programs following Celgene’s exercise of an option for a given program, or if all of Celgene’s options under the Agreement expire without Celgene exercising any of its options. The Agreement will also terminate, on a program-by-program basis, on the expiration of the option term, if Celgene fails to exercise its option for such program. The Company may also terminate the Agreement with respect to one or more programs in the event that Celgene challenges the licensed patents with respect to such program. If Celgene does not exercise its option with respect to a biologic therapeutic program before such option expires, the Company retains worldwide rights to such program, except that if Celgene exercises its option to obtain a license for either the demcizumab or the navicixizumab program, then for so long as such license is in effect, the Company cannot develop or commercialize products under the other of such two programs. In addition, under certain termination circumstances, the Company would also have worldwide rights to the terminated biologic therapeutic programs. The Company’s deliverables under the arrangement with Celgene are research and development services, including the obligation that the Company provides the resultant data to Celgene, which are accounted for as a single unit of accounting. The Company has determined that the options to license programs are substantive options. Additionally, as a result of the uncertain outcome of the discovery, research and development activities, the Company is at risk with regard to whether Celgene will exercise the options. Accordingly, the options are not considered deliverables at the inception of the arrangement and the associated opt-in payments are not included in allocable arrangement consideration. The Company has identified the initial arrangement consideration to be approximately $156.7 million which will be recognized on a straight-line basis over the estimated period of performance of 12 years. Due to the uncertain timeline associated with the deliverables at the outset of the Agreement, the Company determined it will use 12 years, which is the maximum period under the Agreement for Celgene to exercise its options. The Company will reevaluate the estimated performance period at each reporting period. In November 2014, the Company received a designation notice from Celgene relating to the Company’s anti-RSPO3 product candidate, OMP-131R10, which is currently in preclinical testing. This designation triggered a $2.5 million payment due to the Company from Celgene under the Celgene Agreement. In December 2015, the Company achieved the safety milestone and received a designation notice from Celgene for anti-TIGIT (OMP-313M32). The milestone achievement was based on an analysis of available demcizumab Phase Ib and blinded interim Phase II clinical trial safety. This milestone achievement and the designation triggered a $70.0 million and $2.5 million payment, respectively, due to the Company from Celgene under the Celgene Agreement. The $70.0 million safety milestone was considered a non-substantive milestone and was recorded as deferred revenue as of December 31, 2015, which will be recognized as revenue ratably over the estimated period of performance. The $2.5 million designation payment was recognized as collaboration revenue in 2015. In addition, the Company recognized As of December 31, 2016, the Company was eligible to receive in its collaboration with Celgene up to $15.0 million in future development milestones across all biologic programs, prior to the point that Celgene exercises its options. The Company is also eligible to receive up to approximately $240.0 million of contingent consideration if Celgene exercises all its options for the biologic and small molecule therapeutic programs. Celgene will be responsible for all further development and commercialization following the exercise of the options for specified programs. If Celgene successfully develops and commercializes all of the product candidates, the Company could receive additional contingent consideration of up to approximately $2.8 billion for the achievement of specified development, regulatory, and commercial milestones (up to $2.7 billion for biologics and $95.0 million for small molecules). As all contingent consideration is based solely on the performance of Celgene, the Company would recognize the contingent payments upon receipt immediately as collaboration revenue if the Company had no further performance obligations under the Agreement.

Lonza Sales AG Agreement

Lonza Sales AG Agreement	12 Months Ended
	Dec. 31, 2016
Research And Development [Abstract]
Lonza Sales AG Agreement	11. Lonza Sales AG Agreement In August 2012, the Company entered into a multi-product license agreement with Lonza Sales AG (“Lonza”). This agreement relates to the process development and manufacturing of the Company’s biologics portfolio with Lonza. Under the multi-product license agreement, the Company receives licenses to utilize Lonza’s glutamine synthetase gene expression system and related technologies for commercial production of the Company’s product candidates. Under this license agreement, the Company paid an upfront payment of $488,000 which was recorded to research and development expense during 2012 and is obligated to pay Lonza certain payments up to £1.4 million (approximately $2.3 million) on achievement of specified events for each licensed product, and royalties up to the very low single digits on sales of its licensed products. There has been no further payment made by the Company to Lonza pursuant to the license agreement for the years ended December 31, 2016 and 2015. The multi-product license agreement shall remain in force on a product by product and country by country basis until expiration of the Company’s obligation to make payments to Lonza with respect to such product in such country. The agreement can otherwise be terminated by the Company for any reason or no reason upon advance written notice to Lonza, or by either the Company or Lonza upon the other party’s material breach of the agreement, or if the other party ceases to carry on business. Lonza may also terminate the licenses granted under the agreement if the Company challenges any of the Lonza patent rights.

Stockholder_s Equity

Stockholder’s Equity	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Stockholder’s Equity	12. Stockholder’s Equity Stock Incentive Plans 2004 Plan The Company granted options under its 2004 Stock Incentive Plan (the “2004 Plan”) until July 2013 when it was terminated as to future awards, although it continues to govern the terms of options that remain outstanding under the 2004 Plan. The 2004 Plan provided for the award of restricted shares, grants of incentive and nonstatutory stock options, and sales of shares of the Company’s common stock. Awards can be made to employees, outside directors, and consultants of the Company. Stock options granted generally vest over a period of five years from the date of grant, with 20% of the total grant vesting on the first anniversary of the option vesting commencement date and 1/48 of the remaining grant vesting each month thereafter. Restricted stock issuances and early exercise of stock options were subject to the Company’s right of repurchase at the original issuance price, which right lapses over the vesting period of the stock. In connection with the Board of Directors and stockholders approval of the 2013 Plan, all remaining shares available for future award under the 2004 Plan were transferred to 2013 Plan, and the 2004 Plan was terminated as to future awards. 2013 Plan In July 2013, the Company’s Board of Directors and stockholders approved the 2013 Equity Incentive Award Plan (the “2013 Plan”). Under the 2013 Plan, the Company initially reserved 500,000 shares of common stock for issuance as of its effective date of July 17, 2013, plus 90,125 shares which were then available for issuance under the Company’s 2004 Plan. The number of shares reserved for issuance under the 2013 Plan will increase by the number of shares represented by awards outstanding under the 2004 Plan that are forfeited or lapse unexercised and which following July 17, 2013 are not issued under the 2004 Plan. Additionally, on the first day of each calendar year, beginning in 2014 and ending in 2023, the number of shares in the reserve will increase by the least of 1,500,000 shares, 4% of the shares of the Company’s common stock outstanding (on an as-converted basis) on the last day of the immediately preceding fiscal year or such smaller number of shares of stock as determined by the Company’s Board of Directors. The 2013 Plan authorizes discretionary grants of incentive stock options, nonqualified stock options, restricted stock, restricted stock units, performance awards, dividend equivalents, stock payments, deferred stock, deferred stock units, and stock appreciation rights to employees and consultants of the Company, or any of its qualifying affiliates, and to members of the Board of Directors. The exercise price per share subject to each option shall not be less than 100% of the fair value of the common stock on the date of grant. In addition, in the case of incentive stock options granted to a greater than 10% stockholder, such price shall not be less than 110% of the fair value on the date the option is granted. The term of the options shall not be more than 10 years from the grant date, or 5 years from the date an incentive stock option is granted to a greater than 10% stockholder. Stock options granted generally vest over a period of four years from the date of grant, with 25% of the total grant vesting on the first anniversary of the option vesting commencement date and 1/48th of the original grant vesting each month thereafter for stock options granted upon hiring, and with 1/48th of the total grant vesting each month after the option vesting commencement date for any stock options granted after the hiring date. As of December 31, 2016, a total of 4,208,201 shares of common stock have been authorized under the 2013 Plan. As of December 31, 2016, a total of 3,154,753 shares are subject to options and restricted stock units (“RSUs”) outstanding under the 2013 Plan. There are 1,745,568 shares subject to options outstanding under the 2004 Plan as of December 31, 2016, which will become available for issuance under the 2013 Plan to the extent the options are forfeited or lapse unexercised without issuance of such shares under the 2004 Plan. On January 1, 2017, an additional 1,484,583 shares of our common stock became available for future issuance as a result of the annual increase provision in the 2013 Plan. Summary of Activity The following table summarizes the Company’s stock options and RSU award activity under 2004 Plan and 2013 Plan including grants to nonemployees for the periods presented below (in thousands, except exercise prices and contractual life): Shares Available for Grant of Options and Awards Options and Awards Outstanding Weighted Average Exercise Price per Share Weighted Average Remaining Contractual Life Aggregate Intrinsic Value Balances at December 31, 2013 117 2,930 $ 5.90 Options authorized 1,176 — — Options granted (1,027 ) 1,027 22.50 RSUs granted (294 ) 294 — Options exercised — (382 ) 2.83 Options forfeited 47 (47 ) 22.28 Balances at December 31, 2014 19 3,822 10.84 Options authorized 1,194 — — Options granted (1,139 ) 1,139 21.97 Options exercised — (196 ) 3.05 Options forfeited 63 (63 ) 13.61 RSUs forfeited 8 (8 ) — Balances at December 31, 2015 145 4,694 14.02 Options authorized 1,205 — — Options granted (225 ) 225 13.19 RSUs granted (418 ) 418 — Options exercised — (101 ) 3.19 RSU vested — (71 ) — Options forfeited 207 (207 ) 20.34 RSUs forfeited 57 (57 ) — Balances at December 31, 2016 971 4,901 $ 13.95 5.14 $ 10,740 Vested and expected to vest— December 31, 2016 4,868 $ 13.91 5.12 $ 10,723 Vested—December 31, 2016 2,991 $ 11.35 4.31 $ 6,302 Stock Options The aggregate intrinsic value of options exercised were $0.8 million, $4.2 million and $8.9 million for the years ended December 31, 2016, 2015, and 2014, respectively. The aggregate intrinsic value of stock options outstanding was $6.3 million as of December 31, 2016, which represents the value of the Company’s closing stock price as of December 31, 2016 in excess of the weighted-average exercise price multiplied by the number of options outstanding. The weighted-average grant date estimated fair value of all options granted were $8.23, $12.99 and $13.90 per share during the years ended December 31, 2016, 2015 and 2014, respectively. Restricted Stock Units The total fair value of RSUs vested was $1.6 million during the year ended December 31, 2016. There were no RSUs vested in 2015 and 2014. The aggregate intrinsic value of the non-vested RSUs was $4.4 million as of December 31, 2016. The weighted-average grant date estimated fair values of RSUs granted were $11.34 and $31.03 during the years ended December 31, 2016 and 2014, respectively. There were no RSUs granted in 2015. In March 2014, the Company awarded 293,980 RSUs under the 2013 Plan. The RSUs are generally scheduled to vest at the end of three years at March 31, 2017. However, the vesting of 25% of the awarded RSUs was subject to both a performance-based condition and a service condition. The performance-based condition was achieved in the fourth quarter of fiscal year 2015. Stock-based compensation expense related to these RSUs were $1.4 million, $3.8 million and $2.3 million for the year ended December 31, 2016, 2015 and 2014, respectively. Employee Stock Purchase Plan The Company’s Employee Stock Purchase Plan (the “ESPP”) allows eligible employees to purchase shares of the Company’s common stock at a discount through payroll deductions of up to 15% of their eligible compensation, subject to any plan limitations. The ESPP provides for six-month offering periods, and at the end of each offering period, employees are able to purchase shares at 85% of the lower of the fair market value of the Company’s common stock on the first trading day of the offering period or on the last day of the offering period. As of December 31, 2016, a total of 1,193,620 shares of common stock have been authorized and 944,852 shares of common stock are available for future issuance under the Company’s ESPP. On January 1, 2017, an additional 350,000 shares of our common stock became available for future issuance as a result of the annual increase provision in the ESPP plan. During the years ended December 31, 2016, 2015 and 2014, employees purchased an aggregate of 111,633 shares, 71,226 shares and 65,909 shares under the Company’s ESPP, respectively, at a weighted-average price per share of $8.21, $16.58 and $15.21, respectively. During the years ended December 31, 2016, 2015 and 2014, the weighted-average fair value per share granted under the Company’s ESPP were $5.06, $7.00 and $8.11, respectively. Stock-Based Compensation Employee stock-based compensation expense was calculated based on awards expected to vest and has been reduced for estimated forfeitures. Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. Stock-based compensation expense recognized was as follows (in thousands): Year Ended December 31, 2016 2015 2014 Research and development $ 5,892 $ 6,113 $ 3,600 General and administrative 5,239 4,653 2,594 Total $ 11,131 $ 10,766 $ 6,194 As of December 31, 2016, the Company had $14.4 million, $4.6 million and $74,000 of unrecognized compensation expense related to unvested stock options, RSUs and ESPP, respectively, which are expected to be recognized over an estimated weighted-average period of 2.3 years, 1.5 years and 0.2 years, respectively. Fair Value Disclosures The fair value of stock options granted and purchases under the Company’s ESPP is estimated using the Black-Scholes option pricing model. The fair value of stock options granted was estimated as of the grant date using the following assumptions: Year Ended December 31, 2016 2015 2014 Weighted-average volatility 71.9% 62.6% 66.3% Weighted-average expected term (years) 5.8 6.2 6.2 Risk-free interest rate 1.5% 2.1% 2.1% Expected dividend yield — — — The fair value of stock purchase rights granted under the Company’s ESPP was estimated using the following assumptions: Year Ended December 31, 2016 2015 2014 Weighted-average volatility 45.4%–104.5% 51.1%–72.5% 65.7%–115.4% Weighted-average expected term (years) 0.5 0.5 0.5 Risk-free interest rate 0.26%–0.50% 0.05%–0.08% 0.05%–0.08% Expected dividend yield — — — Volatility Since the Company has limited information on the volatility of its common stock due to no significant trading history, the expected stock price volatility was calculated based on a blend of the historical volatilities of the Company’s own stock and of the common stock of comparable publicly traded biopharmaceutical companies over a period equal to the expected term of the stock option grants. The comparable companies were chosen based on their similar size, stage in the life cycle, and financial leverage to the Company. Expected Term The Company has very limited historical information to develop reasonable expectations about future exercise patterns and post-vesting employment termination behavior for its stock-option grants. As such, the expected term was estimated using the simplified method. Risk-Free Rate The risk-free interest rate assumption is based on the zero-coupon U.S. Treasury instruments on the date of grant with a maturity date consistent with the expected term of the Company’s stock option grants. Expected Dividend Yield To date, the Company has not declared or paid any cash dividends and does not have any plans to do so in the future. Therefore, the Company used an expected dividend yield of zero. Common Stock Issuance under At-the-Market Agreement Pursuant to a sales agreement (the “ATM Agreement”) with Cantor Fitzgerald & Co. (“Cantor Fitzgerald”), the Company may issue and sell up to $50.0 million of its common stock in one or more at-the-market offerings, under its shelf registration statement on Form S-3 filed on June 12, 2015. Under the ATM Agreement, the Company agreed to pay Cantor Fitzgerald a commission of 3.0% of the aggregate gross proceeds from each sale of its shares thereunder. For the year ended December 31, 2016, the Company sold 388,166 shares under the ATM Agreement at a weighted average price of $12.59 per share, resulting in aggregate net proceeds of $4.7 million, net of offering costs. Public Offering of Common Stock On August 23, 2016, the Company closed the sale of an aggregate of 6,325,000 shares of our common stock, at a public offering price of $10.00 per share. The shares were issued pursuant to a prospectus supplement filed with the SEC on August 17, 2016, and related prospectus, pursuant to the Company’s shelf registration statement on Form S-3 filed on June 12, 2015. The Company received net offering proceeds of approximately $59.2 million, net of underwriting discounts and commissions and offering costs.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income Taxes	13. Income Taxes For the years ended December 31, 2016 and 2015, the Company recorded an income tax provision of $14,000 and $20,000, respectively, due to interest on uncertain tax positions. For the year ended December 31, 2014, the Company recorded an income tax benefit of $0.5 million due primarily to the recognition of additional tax attributes that can offset alternative minimum tax as a result of the carryback of net operating losses. Loss before income taxes for the years ended December 31, 2016, 2015 and 2014 was from the United States. The components of the provision (benefit) for income taxes are as follows (in thousands): Year Ended December 31, 2016 2015 2014 Current: Federal $ 13 $ 19 $ (10,841 ) State 1 1 1 Total 14 20 (10,840 ) Deferred: Federal — — 10,331 State — — — Total — — 10,331 Income tax provision (benefit) $ 14 $ 20 $ (509 ) The reconciliation of the statutory federal income tax rate to the Company’s effective tax rate is as follows: Year Ended December 31, 2016 2015 2014 Tax at statutory federal rate 35 % 35 % 35 % State tax—net of federal benefit 1 3 — Research and development credit 8 9 12 Change in valuation allowance (42 ) (46 ) (45 ) Other (2 ) (1 ) (1 ) Income tax (provision) benefit — % — % 1 % Net deferred tax assets as of December 31, 2016 and 2015 consist of the following (in thousands): Year Ended December 31, 2016 2015 Deferred tax assets: Net operating loss carryforwards $ 58,760 $ 28,833 Accruals 3,520 1,126 Tax credit carryovers 53,047 36,786 Deferred revenue 63,006 70,428 Other 6,668 5,092 Gross deferred tax assets 185,001 142,265 Deferred tax liability — (151 ) Valuation allowance (185,001 ) (142,114 ) Net deferred tax assets $ — $ — The valuation allowance increased by $42.9 million and $39.3 million for the year ended December 31, 2016 and 2015, respectively. The tax benefit of deductible temporary differences or carryforwards is recorded as a deferred tax asset to the extent that management assesses the realization is “more likely than not.” Future realization of the tax benefit ultimately depends on the existence of sufficient taxable income within the carryback or carryforward period available under the tax law. At December 31, 2016 and 2015, the Company has set up valuation allowances against all federal and state deferred tax assets because based on all available evidence, these deferred tax assets are not more likely than not to be realizable. At December 31, 2016, the Company had federal and state net operating loss carryforwards aggregating approximately $162.8 million and $98.4 million, respectively. These federal and California net operating loss carryforwards will begin to expire in 2023 and 2017, respectively, if not utilized. At December 31, 2016, the Company also had federal and California research and development credit carryforwards aggregating approximately $51.5 million and $18.0 million, respectively. The federal credits will expire in 2025, if not utilized. California research and development credits have no expiration dat e. At December 31, 2016, the Company also had federal orphan drug credit and alternative minimum tax carryforwards of approximately $30.7 million and $2.6 million, respectively. The federal orphan drug credits will begin to expire in 2034, if not utilized. Alternative minimum tax credits have no expiration date. Utilization of the net operating loss and tax credits carryforwards may be limited by “ownership change” rules, as defined in Section 382 of the Internal Revenue Code of 1986, as amended, and similar state provisions. This annual limitation may result in the expiration of the net operating losses and credits before utilization. The Company has performed an analysis to determine whether an “ownership change” has occurred from inception to December 31, 2016. Based on this analysis, management has determined that $0.7 million in federal and $0.7 million in California net operating losses generated during that period will expire without being used. The Company recognizes the financial statements effects of a tax position when it is more likely than not, based on technical merits, that the position will be sustained upon examination. A reconciliation of the Company’s unrecognized tax benefits is as follows (in thousands): December 31, 2016 2015 2014 Balance at beginning of year $ 10,022 $ 5,434 $ 4,464 Increase related to current year tax provision 4,238 4,668 1,539 Increase related to prior year tax provision — 10 — Decrease related to prior year tax provision — (90 ) (569 ) Balance at end of year $ 14,260 $ 10,022 $ 5,434 The unrecognized tax benefits, if recognized and in absence of full valuation allowance, would impact the income tax provision by $13.1 million and $9.0 million as of December 31, 2016 and 2015, respectively. As of December 31, 2016, we do not believe that it is reasonably possible that our unrecognized tax benefits will significantly change in the next 12 months. The Company has elected to include interest and penalties as a component of tax expense. The Company accrued approximately $14,000 of interest and penalties during 2016. As of December 31, 2016 and 2015, the Company had recognized a liability for interest and penalties of approximately $71,000 and $57,000, respectively. The Company files federal and state income tax returns in the U.S. Tax years from 2004 forward remain open to examination due to the carryover of net operating losses and other tax attributes.

Net Loss per Common Share

Net Loss per Common Share	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Net Loss per Common Share	14. Net Loss per Common Share The following outstanding common stock equivalents were excluded from the computation of diluted net loss per common share for the periods presented because including them would have been antidilutive: Year Ended December 31, 2016 2015 2014 Options to purchase common stock 4,324,631 4,407,686 3,528,032 RSUs 575,690 286,071 293,980 4,900,321 4,693,757 3,822,012

Selected Quarterly Financial Da

Selected Quarterly Financial Data	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data	15. Selected Quarterly Financial Data (Unaudited) Selected quarterly results from operations for the years ended December 31, 2016 and 2015 are as follows (in thousands, except per share amounts): 2016 Quarter Ended March 31 June 30 September 30 December 31 Total revenue $ 6,350 $ 6,665 $ 5,919 $ 6,219 Operating expenses 33,597 34,481 31,854 28,608 Net loss (27,213 ) (27,691 ) (25,864 ) (22,334 ) Basic and diluted net loss per common share (0.90 ) (0.91 ) (0.77 ) (0.60 ) 2015 Quarter Ended March 31 June 30 September 30 December 31 Total revenue $ 9,687 $ 4,687 $ 4,687 $ 6,838 Operating expenses 24,227 26,322 29,248 31,659 Net loss (14,529 ) (21,620 ) (24,479 ) (24,779 ) Basic and diluted net loss per common share (0.49 ) (0.72 ) (0.81 ) (0.82 )

Summary of Significant Accoun23

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The Company’s financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”).
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and judgments that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to revenue recognition, preclinical study and clinical trial accruals, fair value of assets and liabilities, income taxes, and stock-based compensation. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results may differ from those estimates.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with original maturities of 90 days or less at the date of purchase to be cash and cash equivalents.
Short-Term Investments	Short-Term Investments Short-term investments consist of debt securities classified as available-for-sale and have maturities greater than 90 days, but less than 365 days from the date of acquisition. Short-term investments are carried at fair value based upon quoted market prices. Unrealized gains and losses on available-for-sale securities are excluded from earnings and were reported as a component of accumulated other comprehensive income (loss). The cost of available-for-sale securities sold is based on the specific-identification method.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash and short-term investments. Cash and short-term investments are invested through banks and other financial institutions in the United States. Such deposits may be in excess of insured limits. The Company maintains cash and investments with various high credit quality and capitalized financial institutions.
Property and Equipment	Property and Equipment Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization is calculated using the straight-line method over the estimated useful lives of the assets, which range from three to five years. Leasehold improvements are amortized over the shorter of their estimated useful lives or the remaining life of the lease at the time the asset is placed into service.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The carrying value of long-lived assets, including property and equipment, are reviewed for impairment whenever events or changes in circumstances indicate that the asset may not be recoverable. An impairment loss is recognized when the total of estimated future undiscounted cash flows, expected to result from the use of the asset and its eventual disposition, are less than its carrying amount. Impairment, if any, would be assessed using discounted cash flows or other appropriate measures of fair value. Through December 31, 2016, there have been no such impairment losses.
Revenue Recognition	Revenue Recognition The Company generates substantially all its revenue from collaborative research and development agreements with pharmaceutical companies. The terms of the agreements may include nonrefundable upfront payments, milestone payments, other contingent payments and royalties on any product sales derived from collaborations. These multiple element arrangements are analyzed to determine whether the deliverables can be separated or whether they must be accounted for as a single unit of accounting. The determination of stand-alone value is generally based on whether any deliverable has stand-alone value to the customer. The Company determines how to allocate arrangement consideration to identified units of accounting based on the selling price hierarchy provided under the relevant guidance. The selling price used for each unit of accounting is based on vendor-specific objective evidence, if available, third-party evidence if vendor-specific objective evidence is not available or estimated selling price if neither vendor-specific nor third-party evidence is available. Management may be required to exercise considerable judgment in determining whether a deliverable is a separate unit of accounting and in estimating the selling prices of identified units of accounting for new agreements. Typically, the Company has not granted licenses to collaborators at the beginning of its arrangements and thus there are no delivered items separate from the research and development services provided. As such, upfront payments are recorded as deferred revenue in the balance sheet and are recognized as collaboration revenue over the estimated period of performance that is consistent with the terms of the research and development obligations contained in the collaboration agreement. The Company regularly reviews the estimated period of performance based on the progress made under each arrangement. Payments that are contingent upon achievement of a substantive milestone are recognized in their entirety in the period in which the milestone is achieved. Milestones are defined as an event that can only be achieved based on the Company’s performance and there is substantive uncertainty about whether the event will be achieved at the inception of the arrangement. Events that are contingent only on the passage of time or only on counterparty performance are not considered milestones. Further, the amounts received must relate solely to prior performance, be reasonable relative to all of the deliverables and payment terms within the agreement and commensurate with the Company’s performance to achieve the milestone after commencement of the agreement. Other contingent payments received for which payment is contingent solely on the results of a collaborative partner’s performance (bonus payments) are not accounted for using the milestone method. Such bonus payments will be recognized as revenue when collectability is reasonably assured. Amounts received prior to satisfying the revenue recognition criteria are recorded as deferred revenue in the Company’s balance sheets. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as current liabilities. The Company recognizes revenue for reimbursements of research and development costs under collaboration agreements as the services are performed. The Company records these reimbursements as revenue on a gross basis and not as a reduction of research and development expenses, as the Company has the risks and rewards as the principal in the research and development activities. Payments related to options to license the Company’s program candidates are considered substantive if, at the inception of the arrangement, the Company is at risk as to whether the collaboration partner will choose to exercise the option. Factors that the Company considers in evaluating whether an option is substantive include the overall objective of the arrangement, the benefit the collaborator might obtain from the arrangement without exercising the option, the cost to exercise the option and the likelihood that the option will be exercised. For arrangements under which an option is considered substantive, the Company does not consider the item underlying the option to be a deliverable at the inception of the arrangement and the associated opt-in payments are not included in allocable arrangement consideration, assuming the option is not priced at a significant and incremental discount. Conversely, for arrangements under which an option is not considered substantive or if an option is priced at a significant and incremental discount, the Company would consider the item underlying the option to be a deliverable at the inception of the arrangement and a corresponding amount would be included in allocable arrangement consideration.
Customer Concentration	Customer Concentration Customers whose collaboration revenue accounted for 10% or more of total revenues were as follows: Year Ended December 31, 2016 2015 2014 GlaxoSmithKline LLC (“GSK”) * 25% 31% Bayer Pharma AG (“Bayer”) * 14% 30% Celgene Corporation (“Celgene”) 87% 61% 39% * less than 10%
Research and Development Expenses	Research and Development Expenses Research and development costs are expensed as incurred. Research and development costs consist of salaries and other personnel-related expenses, including associated stock-based compensation, consulting fees, lab supplies, and facility costs, as well as fees paid to other entities that conduct certain research, development and manufacturing activities on behalf of the Company.
Clinical Trial Accruals	Clinical Trial Accruals Clinical trial costs are a component of research and development expenses. The Company accrues and expenses clinical trial activities performed by third parties based upon actual work completed in accordance with agreements established with clinical research organizations and clinical sites. The Company determines the actual costs through discussions with internal personnel and external service providers as to the progress or stage of completion of trials or services and the agreed-upon fee to be paid for such services. Nonrefundable advance payments for goods and services that will be used or rendered in future research and development activities, are deferred and recognized as expense in the period that the related goods are delivered or services are performed.
Stock-Based Compensation	Stock-Based Compensation The Company recognizes compensation expense for all share-based payment awards made to employees and directors based on estimated fair values. For employee stock options, the Company determines the grant date fair value of the awards using the Black-Scholes option-pricing model and generally recognizes the fair value as stock-based compensation expense on a straight-line basis over the vesting period of the respective awards. Stock-based compensation expense is based on the value of the portion of stock-based payment awards that is ultimately expected to vest. As such, the Company’s stock-based compensation is reduced for the estimated forfeitures at the date of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. For restricted stock, the compensation cost for these awards is based on the closing price of the Company’s common stock on the date of grant and recognized as compensation expense on a straight-line basis over the requisite service period. The Company accounts for equity instruments issued to nonemployees based on their fair values on the measurement dates using the Black-Scholes option-pricing model. The estimated fair values of the options granted to nonemployees are remeasured as they vest. As a result, the noncash charge to operations for nonemployee options with vesting conditions is affected each reporting period by changes in the fair value of the Company’s common stock.
Leases	Leases The Company rents its office space and facilities under cancelable and non-cancelable operating lease agreements and recognizes related rent expense on a straight-line basis over the term of the lease. The Company’s lease agreements contain rent holidays, scheduled rent increases, lease incentives and renewal options. Rent holidays and scheduled rent increases are included in the determination of rent expense to be recorded over the lease term. Lease incentives are recognized as a reduction of rent expense on a straight-line basis over the term of the lease. The Company does not assume renewals in its determination of the lease term unless they are deemed to be reasonably assured at the inception of the lease. The Company begins recognizing rent expense on the date that the Company obtains the legal right to use and control the leased space.
Income Taxes	Income Taxes The Company accounts for income taxes using the liability method under which deferred tax assets and liabilities are determined based on differences between financial reporting and tax basis of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. Valuation allowances are established when necessary to reduce deferred tax assets to the amount which is more likely than not to be realizable. The recognition, derecognition and measurement of a tax position is based on management’s best judgment given the facts, circumstances and information available at each reporting date. The Company’s policy is to recognize interest and penalties related to the underpayment of income taxes as a component of income tax expense. To date, there have been no interest or penalties charged in relation to the unrecognized tax benefits.
Net Loss per Common Share	Net Loss per Common Share Basic net loss per common share is calculated by dividing the net loss by the weighted-average number of common shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per common share is computed by dividing the net loss by the weighted-average number of common shares and common share equivalents outstanding for the period determined using the treasury-stock method. For purposes of this calculation, potentially dilutive securities consisting of stock options and restricted stock units are considered to be common stock equivalents and were excluded in the calculation of diluted net loss per common share because their effect would be anti-dilutive for all periods presented.
Newly Adopted and Recent Accounting Pronouncements	Newly Adopted and Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, 2014-09, Revenue from Contracts with Customers: Topic 606 In March, April, May and December 2016, the FASB issued ASU 2016-08, Revenue from Contracts with Customers: Principal versus Agent Considerations , ASU 2016-10, Revenue from Contracts with Customers: Identifying Performance Obligations and Licensing , ASU 2016-12, Revenue from Contracts with Customers: Narrow-Scope Improvements and Practical Expedients to provide supplemental adoption guidance and clarification to ASU 2014-09 and ASU 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers , respectively. The effective date for these new standards is the same as the effective date and transition requirements for ASU 2014-09. The Company expects to adopt ASU 2014-09 in the first quarter of 2018 using the modified retrospective method. The adoption of ASU 2014-09 may have a material effect on the Company’s financial statements. To date, we have derived our revenues collaboration agreements. The consideration the Company is eligible to receive under these agreements includes upfront payments, research and development funding, and milestone payments. Each collaboration agreement is unique and will need to be assessed separately under the five-step process under the new standard. The Company has started its preliminary assessment of our active license and collaboration agreements. The Company expects that its evaluation of the accounting for collaboration agreements under the new revenue standard could identify material changes from the current accounting treatment. ASU 2014-09 differs from the current accounting standard in many respects, such as in the accounting for variable consideration, including milestone payments. Under our current accounting policy, the Company recognizes milestone revenue using the milestone method specified in ASC 605-28, which generally results in the recognition of the milestone payment as revenue in the period that the milestone is achieved. However, under the new accounting standard, it is possible to start to recognize milestone revenue before the milestone is achieved, subject to management’s assessment of whether it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. In addition, the current accounting standards include a presumption that revenue from up-front non-refundable fees would be recognized ratably over the performance period, unless another attribution method was determined to more closely approximate the delivery of the goods or services to the customer. The new accounting standard does not have a presumption that entities would default to a ratable attribution approach and will require entities to determine an appropriate attribution method using either output or input methods. As such, the amount and timing of revenue recognition for the Company’s collaboration agreements may change under the new revenue standard. In August 2014, the FASB issued ASU No. 2014-15 (Subtopic 205-40) “Presentation of Financial Statements—Going Concern: Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern.” ASU 2014-15 provides guidance about management’s responsibility to evaluate whether or not there is substantial doubt about the Company’s ability to continue as a going concern and to provide related footnote disclosure. ASU 2014-15 is effective for fiscal years ending after December 15, 2016, and for interim and annual periods therein, with early adoption permitted. The Company adopted this guidance in the fourth quarter of 2016. The adoption of the standard did not have material impact on the Company’s financial statements. In February 2016, the FASB issued ASU 2016-02 “Leases.” ASU 2016-02 amends a number of aspects of lease accounting In March 2016, the FASB issued ASU 2016-09 “Improvements to Employee Share-Based Payment Accounting.” ASU 2016-09 simplifies several aspects of employee share-based payment accounting, including the income tax consequences, classification of awards as either equity or liabilities and classification on the statement of cash flows. This guidance will become effective for the Company beginning in the first quarter of 2017, with early adoption permitted. The Company plans to adopt the guidance in the first quarter of 2017. The Company is evaluating the impact of the adoption of this standard on its financial statements.

Summary of Significant Accoun24

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Schedule of Collaboration Revenue	Customers whose collaboration revenue accounted for 10% or more of total revenues were as follows: Year Ended December 31, 2016 2015 2014 GlaxoSmithKline LLC (“GSK”) * 25% 31% Bayer Pharma AG (“Bayer”) * 14% 30% Celgene Corporation (“Celgene”) 87% 61% 39% * less than 10%

Cash and Investments (Tables)

Cash and Investments (Tables)	12 Months Ended
	Dec. 31, 2016
Cash And Cash Equivalents [Abstract]
Schedule of Fair Value of Securities, Not Including Cash	The fair value of securities, not including cash at December 31, 2016 and 2015 were as follows (in thousands): December 31, 2016 Amortized Gross Unrealized Fair Cost Gains Losses Value U.S. treasury bills $ 147,360 $ 260 $ — $ 147,620 Total $ 147,360 $ 260 $ — $ 147,620 Classified as: Short-term investments $ 147,620 As of December 31, 2016, the Company had a total of $184.6 million in cash and short-term investments, which includes $37.0 million in cash and $147.6 million in short-term investments. December 31, 2015 Amortized Gross Unrealized Fair Cost Gains Losses Value U.S. treasury bills $ 118,815 $ 40 $ (20 ) $ 118,835 Total $ 118,815 $ 40 $ (20 ) $ 118,835 Classified as: Short-term investments $ 118,835

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Summary of Company's Financial Assets and Liabilities Subject to Fair Value Measurements on Recurring Basis	The Company’s financial assets and liabilities subject to fair value measurements on a recurring basis and the level of inputs used in such measurements were as follows (in thousands): December 31, 2016 Level 1 Level 2 Level 3 Total Assets: U.S. treasury bills $ — $ 147,620 $ — $ 147,620 Total $ — $ 147,620 $ — $ 147,620 December 31, 2015 Level 1 Level 2 Level 3 Total Assets: U.S. treasury bills $ — $ 118,835 $ — $ 118,835 Total $ — $ 118,835 $ — $ 118,835

Property and Equipment, net (Ta

Property and Equipment, net (Tables)	12 Months Ended
	Dec. 31, 2016
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment, net	Property and equipment, net consist of the following (in thousands): December 31, 2016 2015 Computer equipment and software $ 1,897 $ 1,828 Furniture and fixtures 527 498 Laboratory equipment 11,452 10,286 Leasehold improvements 9,095 9,064 22,971 21,676 Less accumulated depreciation and amortization (18,500 ) (16,851 ) Property equipment, net $ 4,471 $ 4,825

Accrued Liabilities (Tables)

Accrued Liabilities (Tables)	12 Months Ended
	Dec. 31, 2016
Payables And Accruals [Abstract]
Schedule of Accrued Liabilities	Accrued liabilities consist of the following (in thousands): December 31, 2016 2015 Research and development related $ 3,143 $ 4,941 Compensation related 4,922 6,019 Other 534 515 Total accrued liabilities $ 8,599 $ 11,475

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2016
Commitments And Contingencies Disclosure [Abstract]
Summary of Minimum Annual Rental Payments under the Company's Non-cancelable Operating Lease Agreement	As of December 31, 2016, minimum annual rental payments under the Company’s non-cancelable operating lease agreement are as follows (in thousands): Year ending December 31, 2017 $ 1,707 2018 2,323 2019 2,406 2020 2,490 2021 and thereafter 21,387 Total minimum payments $ 30,313

Collaborations (Tables)

Collaborations (Tables)	12 Months Ended
	Dec. 31, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Company Recognized Revenues from Collaboration Agreements	The Company has recognized the following revenues from its collaboration agreements during the years ended December 31, 2016, 2015 and 2014 (in thousands): Year Ended December 31, 2016 2015 2014 GSK: Recognition of upfront payment $ 576 $ 1,123 $ 1,248 Milestone revenue — 5,000 11,000 Other revenue 639 363 — GSK total 1,215 6,486 12,248 Bayer: Recognition of upfront payments 648 3,518 9,756 Milestone revenue — — 2,000 Other revenue 1,457 — — Bayer total 2,105 3,518 11,756 Celgene: Recognition of upfront payment 20,053 13,055 13,055 Milestone revenue — 2,520 2,500 Other revenue 1,780 320 — Celgene total 21,833 15,895 15,555 Total collaboration related revenue $ 25,153 $ 25,899 $ 39,559

Stockholder_s Equity (Tables)

Stockholder’s Equity (Tables)	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Summary of Stock Options and RSU Award Activity under 2004 Plan and 2013 Stock Plan	The following table summarizes the Company’s stock options and RSU award activity under 2004 Plan and 2013 Plan including grants to nonemployees for the periods presented below (in thousands, except exercise prices and contractual life): Shares Available for Grant of Options and Awards Options and Awards Outstanding Weighted Average Exercise Price per Share Weighted Average Remaining Contractual Life Aggregate Intrinsic Value Balances at December 31, 2013 117 2,930 $ 5.90 Options authorized 1,176 — — Options granted (1,027 ) 1,027 22.50 RSUs granted (294 ) 294 — Options exercised — (382 ) 2.83 Options forfeited 47 (47 ) 22.28 Balances at December 31, 2014 19 3,822 10.84 Options authorized 1,194 — — Options granted (1,139 ) 1,139 21.97 Options exercised — (196 ) 3.05 Options forfeited 63 (63 ) 13.61 RSUs forfeited 8 (8 ) — Balances at December 31, 2015 145 4,694 14.02 Options authorized 1,205 — — Options granted (225 ) 225 13.19 RSUs granted (418 ) 418 — Options exercised — (101 ) 3.19 RSU vested — (71 ) — Options forfeited 207 (207 ) 20.34 RSUs forfeited 57 (57 ) — Balances at December 31, 2016 971 4,901 $ 13.95 5.14 $ 10,740 Vested and expected to vest— December 31, 2016 4,868 $ 13.91 5.12 $ 10,723 Vested—December 31, 2016 2,991 $ 11.35 4.31 $ 6,302
Schedule of Stock-Based Compensation Expense	Stock-based compensation expense recognized was as follows (in thousands): Year Ended December 31, 2016 2015 2014 Research and development $ 5,892 $ 6,113 $ 3,600 General and administrative 5,239 4,653 2,594 Total $ 11,131 $ 10,766 $ 6,194
Assumptions Used for Determining Fair Value of Stock Options Using Black-Scholes Valuation Model	The fair value of stock options granted was estimated as of the grant date using the following assumptions: Year Ended December 31, 2016 2015 2014 Weighted-average volatility 71.9% 62.6% 66.3% Weighted-average expected term (years) 5.8 6.2 6.2 Risk-free interest rate 1.5% 2.1% 2.1% Expected dividend yield — — —
Assumptions Used for Determining Fair Value of Stock Purchase Rights Granted Under Company's ESPP Using Black-Scholes Valuation Model	The fair value of stock purchase rights granted under the Company’s ESPP was estimated using the following assumptions: Year Ended December 31, 2016 2015 2014 Weighted-average volatility 45.4%–104.5% 51.1%–72.5% 65.7%–115.4% Weighted-average expected term (years) 0.5 0.5 0.5 Risk-free interest rate 0.26%–0.50% 0.05%–0.08% 0.05%–0.08% Expected dividend yield — — —

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Components of Provision (Benefit) for Income Taxes	The components of the provision (benefit) for income taxes are as follows (in thousands): Year Ended December 31, 2016 2015 2014 Current: Federal $ 13 $ 19 $ (10,841 ) State 1 1 1 Total 14 20 (10,840 ) Deferred: Federal — — 10,331 State — — — Total — — 10,331 Income tax provision (benefit) $ 14 $ 20 $ (509 )
Schedule of Reconciliation of Statutory Federal Income Tax Rate to Company's Effective Tax Rate	The reconciliation of the statutory federal income tax rate to the Company’s effective tax rate is as follows: Year Ended December 31, 2016 2015 2014 Tax at statutory federal rate 35 % 35 % 35 % State tax—net of federal benefit 1 3 — Research and development credit 8 9 12 Change in valuation allowance (42 ) (46 ) (45 ) Other (2 ) (1 ) (1 ) Income tax (provision) benefit — % — % 1 %
Schedule of Net Deferred Tax Assets	Net deferred tax assets as of December 31, 2016 and 2015 consist of the following (in thousands): Year Ended December 31, 2016 2015 Deferred tax assets: Net operating loss carryforwards $ 58,760 $ 28,833 Accruals 3,520 1,126 Tax credit carryovers 53,047 36,786 Deferred revenue 63,006 70,428 Other 6,668 5,092 Gross deferred tax assets 185,001 142,265 Deferred tax liability — (151 ) Valuation allowance (185,001 ) (142,114 ) Net deferred tax assets $ — $ —
Reconciliation of Unrecognized Tax Benefits	A reconciliation of the Company’s unrecognized tax benefits is as follows (in thousands): December 31, 2016 2015 2014 Balance at beginning of year $ 10,022 $ 5,434 $ 4,464 Increase related to current year tax provision 4,238 4,668 1,539 Increase related to prior year tax provision — 10 — Decrease related to prior year tax provision — (90 ) (569 ) Balance at end of year $ 14,260 $ 10,022 $ 5,434

Net Loss per Common Share (Tabl

Net Loss per Common Share (Tables)	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Outstanding Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Common Share	The following outstanding common stock equivalents were excluded from the computation of diluted net loss per common share for the periods presented because including them would have been antidilutive: Year Ended December 31, 2016 2015 2014 Options to purchase common stock 4,324,631 4,407,686 3,528,032 RSUs 575,690 286,071 293,980 4,900,321 4,693,757 3,822,012

Selected Quarterly Financial 34

Selected Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Summary of Selected Quarterly Results from Operations	Selected quarterly results from operations for the years ended December 31, 2016 and 2015 are as follows (in thousands, except per share amounts): 2016 Quarter Ended March 31 June 30 September 30 December 31 Total revenue $ 6,350 $ 6,665 $ 5,919 $ 6,219 Operating expenses 33,597 34,481 31,854 28,608 Net loss (27,213 ) (27,691 ) (25,864 ) (22,334 ) Basic and diluted net loss per common share (0.90 ) (0.91 ) (0.77 ) (0.60 ) 2015 Quarter Ended March 31 June 30 September 30 December 31 Total revenue $ 9,687 $ 4,687 $ 4,687 $ 6,838 Operating expenses 24,227 26,322 29,248 31,659 Net loss (14,529 ) (21,620 ) (24,479 ) (24,779 ) Basic and diluted net loss per common share (0.49 ) (0.72 ) (0.81 ) (0.82 )

Organization - Additional Infor

Organization - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016Segment
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of operating segment	1
Incorporation date	Jul. 31, 2004
Initial Public Offering effective date	Jul. 17, 2013
Initial Public Offering closure date	Jul. 23, 2013

Summary of Significant Accoun36

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016USD ($)
Summary Of Significant Accounting Policies [Line Items]
Impairment of long-lived assets	$ 0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	$ 0
Leasehold Improvements [Member]
Summary Of Significant Accounting Policies [Line Items]
Description of property and equipment over estimated useful lives	shorter of their estimated useful lives or the remaining life of the lease at the time the asset is placed into service
Maximum [Member] | Property and Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, Estimated useful life	5 years
Minimum [Member] | Revenue [Member] | Customer Concentration [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration risk percentage of revenue represented by major customers	10.00%
Minimum [Member] | Property and Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, Estimated useful life	3 years

Summary of Significant Accoun37

Summary of Significant Accounting Policies - Schedule of Collaboration Revenue (Detail) - Revenue [Member] - Customer Concentration [Member] - Collaborative Arrangement [Member]	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
GSK [Member]
Concentration Risk [Line Items]
Collaborative research and development revenue, Percentage		25.00%	31.00%
Bayer [Member]
Concentration Risk [Line Items]
Collaborative research and development revenue, Percentage		14.00%	30.00%
Celgene [Member]
Concentration Risk [Line Items]
Collaborative research and development revenue, Percentage	87.00%	61.00%	39.00%

Summary of Significant Accoun38

Summary of Significant Accounting Policies - Schedule of Collaboration Revenue (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2016
Minimum [Member] | Revenue [Member] | Customer Concentration [Member]
Concentration Risk [Line Items]
Concentration risk percentage of revenue represented by major customers	10.00%

Cash and Investments - Schedule

Cash and Investments - Schedule of Fair Value of Securities, Not Including Cash (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 147,360	$ 118,815
Gross Unrealized Gains	260	40
Gross Unrealized Losses		(20)
Fair Value	147,620	118,835
U.S. Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	147,360	118,815
Gross Unrealized Gains	260	40
Gross Unrealized Losses		(20)
Fair Value	147,620	118,835
Short-Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	$ 147,620	$ 118,835

Cash and Investments - Addition

Cash and Investments - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Total cash and short-term investments	$ 184,600,000	$ 157,300,000
Cash	36,953,000	38,444,000	$ 28,138,000	$ 208,931,000
Short-term investments	147,620,000	118,835,000
Realized gains or losses on available-for-sale securities	$ 0	$ 0
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities, contractual maturity period	1 year	1 year

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Company's Financial Assets and Liabilities Subject to Fair Value Measurements on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Assets:
Assets fair value disclosure	$ 147,620	$ 118,835
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Assets:
Assets fair value disclosure	147,620	118,835
U.S. Treasury Bills [Member]
Assets:
Assets fair value disclosure	147,620	118,835
U.S. Treasury Bills [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Assets:
Assets fair value disclosure	$ 147,620	$ 118,835

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail)	Dec. 31, 2016USD ($)
Fair Value Disclosures [Abstract]
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount	$ 0
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount	0
Fair Value, Liabilities, Level 1 to Level 2 Transfers, Amount	0
Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount	$ 0

Property and Equipment, net - S

Property and Equipment, net - Schedule of Property and Equipment, net (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 22,971	$ 21,676
Less accumulated depreciation and amortization	(18,500)	(16,851)
Property equipment, net	4,471	4,825
Computer Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,897	1,828
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	527	498
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	11,452	10,286
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 9,095	$ 9,064

Property and Equipment, net - A

Property and Equipment, net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property Plant And Equipment [Abstract]
Depreciation expense	$ 1,764	$ 1,643	$ 1,430

Accrued Liabilities - Schedule

Accrued Liabilities - Schedule of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Payables And Accruals [Abstract]
Research and development related	$ 3,143	$ 4,941
Compensation related	4,922	6,019
Other	534	515
Total accrued liabilities	$ 8,599	$ 11,475

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Leased Assets [Line Items]
Operating lease, expiration date	2028-05	2019-01
Operating lease, additional period	3 years	3 years
Total estimated base rent payments		$ 13.8
Base rent obligation on additional space estimated commencement year		2018-06
Lease agreement for additional space termination date		Sep. 16, 2017
Tenant improvement allowance, total		$ 7.3
Rental expense		$ 1.6	$ 1.3	$ 1.3
Additional Office and Laboratory Space
Operating Leased Assets [Line Items]
Operating lease, additional period	10 years

Commitments and Contingencies47

Commitments and Contingencies - Summary of Minimum Annual Rental Payments under the Company's Non-cancelable Operating Lease Agreement (Detail) $ in Thousands	Dec. 31, 2016USD ($)
Commitments And Contingencies Disclosure [Abstract]
2,017	$ 1,707
2,018	2,323
2,019	2,406
2,020	2,490
2021 and thereafter	21,387
Total minimum payments	$ 30,313

License Agreement - Additional

License Agreement - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2004
License Agreements [Line Items]
Up-front fee				$ 10,000
Common shares	37,114,589	30,116,633
Royalties payments to licensor				$ 10,000,000
Legal costs	$ 69,000	$ 65,000	$ 158,000
Common Stock [Member]
License Agreements [Line Items]
Common shares				7,796
Nonvoting Common Stock [Member]
License Agreements [Line Items]
Additional common stock				0.25%

Supply and License Agreements -

Supply and License Agreements - Additional Information (Detail)	1 Months Ended	12 Months Ended
	Jan. 31, 2015USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2016EUR (€)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2016EUR (€)	Dec. 31, 2009USD ($)	Dec. 31, 2009EUR (€)	Dec. 31, 2008USD ($)	Dec. 31, 2008EUR (€)
Supply And License Agreement Commitment [Line Items]
Technology access and subscription fees paid							$ 350,000	€ 250,000	$ 919,000	€ 650,000
Annual license fee		$ 22,000				€ 20,000
Research license agreement expiration		2,020	2,020
GSK [Member]
Supply And License Agreement Commitment [Line Items]
Reimbursement of research and development costs	$ 400,000
MorphoSys AG [Member]
Supply And License Agreement Commitment [Line Items]
Future milestone payments		$ 6,300,000	€ 5,800,000
MorphoSys AG [Member] | GSK [Member]
Supply And License Agreement Commitment [Line Items]
Reimbursement of research and development costs		$ 992,000
Tarextumab Anti-Notch 2/3, OMP-59R5 [Member]
Supply And License Agreement Commitment [Line Items]
Reimbursement percentage		50.00%	50.00%
License Agreement [Member]
Supply And License Agreement Commitment [Line Items]
License agreement year		2006-06	2006-06
GSK [Member]
Supply And License Agreement Commitment [Line Items]
Payments and reimbursements		$ 0		$ 0	$ 0

Collaborations - GSK Strategic

Collaborations - GSK Strategic Alliance - Additional Information (Detail) $ in Thousands

Dec. 31, 2016USD ($)

Dec. 07, 2007USD ($)shares

Jan. 31, 2015USD ($)

Jul. 31, 2014USD ($)

Jan. 31, 2014

Jul. 31, 2012USD ($)

Jul. 31, 2011USD ($)

Dec. 31, 2016USD ($)Agreement

Dec. 31, 2012USD ($)

Dec. 31, 2015USD ($)

Jun. 30, 2013USD ($)

Oct. 31, 2012USD ($)

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Number Of Collaboration Agreements | Agreement

3

Deferred revenue, less current portion

$ 159,373

$ 159,373

$ 179,612

GSK [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Estimated revenue recognition period

5 years

Milestone payments from collaboration partner

$ 5,000

Reimbursement of research and development costs

$ 400

GSK [Member] | July 2011 Amendment [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Estimated revenue recognition period

5 years

4 years

Deferred revenue, less current portion

$ 7,900

Extended estimated completion of clinical trials deliverable

2016-06

GSK [Member] | Collaborative Arrangement [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Deferred revenue

$ 8,000

Decrease in revenue

$ 100

GSK [Member] | Collaborative Arrangement [Member] | Brontictuzumab Anti-Notch 1, OMP-52M51 [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Deferred revenue

$ 3,000

GSK [Member] | Collaborative Arrangement [Member] | Tarextumab Anti-Notch 2/3, OMP-59R5 [Member] | Milestone payment two [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Deferred revenue, revenue recognized

$ 3,000

$ 3,000

GSK [Member] | Collaborative Arrangement [Member] | Tarextumab Anti-Notch 2/3, OMP-59R5 [Member] | Milestone payment one [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Deferred revenue, revenue recognized

$ 8,000

GSK [Member] | Collaborative Arrangement [Member] | Tarextumab [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Initial payment received from collaboration arrangement

25,000

Future development milestone payments

$ 319,500

319,500

Opt-in payment

$ 25,000

$ 25,000

GSK [Member] | Proof of Principle Development Milestone Payments [Member] | Tarextumab Anti-Notch 2/3, OMP-59R5 [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone recognized

$ 5,000

GSK [Member] | IND Acceptance [Member] | Brontictuzumab Anti-Notch 1, OMP-52M51 [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone recognized

5,000

GSK [Member] | First Patient [Member] | Brontictuzumab Anti-Notch 1, OMP-52M51 [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone recognized

$ 4,000

GSK [Member] | Maximum [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Estimated amount to be received for development cost

$ 2,000

GSK [Member] | Series B-2 Convertible Preferred Stock [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Initial payment received from collaboration arrangement

$ 35,000

Number of shares issued | shares

1,441,396

Premium received on number of shares issued

$ 4,300

Deferred revenue

$ 17,500

Collaborations - Company Recogn

Collaborations - Company Recognized Revenues from Collaboration Agreements (Detail) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue		$ 21,277	$ 25,216	$ 39,559
Collaborative Arrangement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue		25,153	25,899	39,559
Collaborative Arrangement [Member] | GSK [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue		1,215	6,486	12,248
Collaborative Arrangement [Member] | GSK [Member] | Recognition of Upfront Payments [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue		576	1,123	1,248
Collaborative Arrangement [Member] | GSK [Member] | Milestone Revenue [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue			5,000	11,000
Collaborative Arrangement [Member] | GSK [Member] | Other Revenue [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue		639	363
Collaborative Arrangement [Member] | Bayer [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue		2,105	3,518	11,756
Collaborative Arrangement [Member] | Bayer [Member] | Recognition of Upfront Payments [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue		648	3,518	9,756
Collaborative Arrangement [Member] | Bayer [Member] | Milestone Revenue [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue				2,000
Collaborative Arrangement [Member] | Bayer [Member] | Other Revenue [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue		1,457
Collaborative Arrangement [Member] | Celgene [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue	$ 2,500	21,833	15,895	15,555
Collaborative Arrangement [Member] | Celgene [Member] | Recognition of Upfront Payments [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue		20,053	13,055	13,055
Collaborative Arrangement [Member] | Celgene [Member] | Milestone Revenue [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue			2,520	$ 2,500
Collaborative Arrangement [Member] | Celgene [Member] | Other Revenue [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue		$ 1,780	$ 320

Collaborations - Bayer Strategi

Collaborations - Bayer Strategic Alliance - Additional Information (Detail) - Bayer [Member] $ in Millions	1 Months Ended			12 Months Ended
	Sep. 30, 2014USD ($)	Oct. 31, 2013USD ($)	Aug. 31, 2013USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2012USD ($)	Dec. 31, 2011USD ($)	Nov. 30, 2015Patient
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and Option Agreement date				Jun. 15, 2010
Estimated revenue recognition period				5 years
Collaborative Arrangement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent consideration payments for regulatory events				$ 185
Number of patients allowed to be added | Patient							6
Number of patients agreed to be added | Patient							6
Decrease in revenue				0.1
Future development milestone payments				10
Collaborative Arrangement [Member] | Achievement of Specified Future Product Sales [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent consideration payments for regulatory events				1,000
Recognition of Upfront Payment [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone recognized				40
Biologic Product [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent consideration payments for regulatory events				387.5
Biologic Product [Member] | Collaborative Arrangement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent consideration payments for regulatory events				135
Future development milestone payments				55
Biologic Product [Member] | Collaborative Arrangement [Member] | Achievement of Specified Future Product Sales [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent consideration payments for regulatory events				862.5
Small Molecules [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent consideration payments for regulatory events				112
Small Molecules [Member] | Collaborative Arrangement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone recognized	$ 2
Contingent consideration payments for regulatory events				50
Future development milestone payments				22
Small Molecules [Member] | Collaborative Arrangement [Member] | Achievement of Specified Future Product Sales [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent consideration payments for regulatory events				140
Vantictumab [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone recognized		$ 15	$ 10	$ 25		$ 20
ipafricept Fzd8-Fc, OMP-54F28 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Initial payment received from collaboration arrangement					$ 5
Deferred revenue					$ 5

Collaborations - Celgene Strate

Collaborations - Celgene Strategic Alliance - Additional Information (Detail)	1 Months Ended	12 Months Ended
	Dec. 31, 2015USD ($)	Dec. 31, 2016USD ($)Program$ / sharesshares	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Nov. 30, 2014USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue		$ 21,277,000	$ 25,216,000	$ 39,559,000
Collaborative Arrangement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of sharing development cost		33.33%
Collaboration revenue		$ 25,153,000	25,899,000	39,559,000
Celgene [Member] | Collaborative Arrangement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and Option Agreement date		Dec. 31, 2013
Number of biologic programs | Program		6
Number of biological program for which company can enter into co-commercialization and co-development agreements | Program		5
Collaboration agreement extension period		2 years
Percentage of sharing development cost		66.66%
Upfront cash payment received		$ 155,000,000
Issuance of common stock in connection with research and collaboration agreement | shares		1,470,588
Common stock price per share | $ / shares		$ 15.13
Proceeds from issuance of common stock		$ 22,200,000
Premium on closing price of common stock value		1,700,000
Common stock, fair market value		$ 20,500,000
Profits and losses sharing percentage		50.00%
Initial arrangement consideration	$ 156,700,000		156,700,000
Estimated revenue recognition period		12 years
Payment receivable under agreement					$ 2,500,000
Deferred revenue	70,000,000		70,000,000
Collaboration revenue	2,500,000	$ 21,833,000	$ 15,895,000	$ 15,555,000
Reimbursement of research and development costs	$ 300,000
Additional contingent consideration for development, regulatory and commercial milestones		2,800,000,000
Celgene [Member] | Collaborative Arrangement [Member] | Demcizumab Program [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Regulatory and commercial milestones payments		791,000,000
Opt-in payment		70,000,000
Celgene [Member] | Collaborative Arrangement [Member] | Anti-RSPO3 Program [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Regulatory and commercial milestones payments		442,800,000
Opt-in payment		37,800,000
Celgene [Member] | Collaborative Arrangement [Member] | Navicixizumab Program [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Regulatory and commercial milestones payments		505,000,000
Opt-in payment		25,000,000
Celgene [Member] | Collaborative Arrangement [Member] | Small Molecules [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Regulatory and commercial milestones payments		107,000,000
Additional contingent consideration for development, regulatory and commercial milestones		95,000,000
Celgene [Member] | Collaborative Arrangement [Member] | Anti-TIGIT Program [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Regulatory and commercial milestones payments		440,000,000
Opt-in payment		35,000,000
Celgene [Member] | Collaborative Arrangement [Member] | RSPO LGR Signaling Pathway [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Regulatory and commercial milestones payments		$ 440,000,000
Number of additional biologic program | Program		2
Celgene [Member] | Collaborative Arrangement [Member] | Undisclosed Pathway [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Regulatory and commercial milestones payments		$ 440,000,000
Number of additional biologic program | Program		2
Celgene [Member] | Collaborative Arrangement [Member] | Biologic Product [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future development milestone payments		$ 15,000,000
Celgene [Member] | Collaborative Arrangement [Member] | Biologic Product [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additional contingent consideration for development, regulatory and commercial milestones		2,700,000,000
Celgene [Member] | Collaborative Arrangement [Member] | Biologic and Small Molecule Therapeutic Programs [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future development milestone payments		$ 240,000,000

Lonza Sales AG Agreement - Addi

Lonza Sales AG Agreement - Additional Information (Detail) - Lonza Sales AG [Member] £ in Millions	12 Months Ended
	Dec. 31, 2012USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2012GBP (£)
Research and Development Arrangement, Contract to Perform for Others [Line Items]
License agreement, upfront payment recorded in research and development expense	$ 488,000
Obligation to pay certain payments	$ 2,300,000	$ 0	$ 0	£ 1.4

Stockholder's Equity - Addition

Stockholder's Equity - Additional Information (Detail) - USD ($)	Aug. 23, 2016	Jul. 17, 2013	Mar. 31, 2014	Jul. 31, 2013	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jan. 01, 2017	Dec. 31, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options vesting original months					5 years 1 month 13 days
Common stock shares authorized					0	0	0
Common stock subject to options outstanding					4,901,000	4,694,000	3,822,000		2,930,000
Intrinsic value of options exercised					$ 800,000	$ 4,200,000	$ 8,900,000
Intrinsic value of options outstanding					$ 6,300,000
Weighted-average grant-date fair value, granted					$ 8.23	$ 12.99	$ 13.90
Stock-based compensation expense					$ 11,131,000	$ 10,766,000	$ 6,194,000
Common Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock issued to employees under ESPP					111,633	71,226	65,909
At-the-Market Offering [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Net proceeds from sale of common stock					$ 4,739,000
Offering proceeds, net of underwriting discounts and commissions and offering costs					$ 4,739,000
At-the-Market Offering [Member] | Common Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares sold					388,166
At-the-Market Offering [Member] | Cantor Fitzgerald & Co [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of sales commission on aggregate gross proceeds					3.00%
Weighted average price per share					$ 12.59
Net proceeds from sale of common stock					$ 4,739,000
At-the-Market Offering [Member] | Cantor Fitzgerald & Co [Member] | Common Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares sold					388,166
Public Offering [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares sold	6,325,000
Net proceeds from sale of common stock					$ 59,170,000
Public offering price per share	$ 10
Offering proceeds, net of underwriting discounts and commissions and offering costs	$ 59,200,000				$ 59,170,000
Public Offering [Member] | Common Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares sold					6,325,000
Offering proceeds, net of underwriting discounts and commissions and offering costs					$ 7,000
Employees Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock available for future issuance under plan					944,852
Common stock shares authorized					1,193,620
Common stock purchased at discount through payroll deductions					15.00%
Employee stock purchase plan, offering period					6 months
Shares purchased lower of the fair market value					85.00%
Common stock issued to employees under ESPP					111,633	71,226	65,909
Weighted-average price per share					$ 8.21	$ 16.58	$ 15.21
Weighted-average grant-date fair value, granted					$ 5.06	$ 7	8.11
Unrecognized stock-based compensation expense					$ 74,000
Estimated weighted-average period					2 months 12 days
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock units vesting period			3 years
Weighted-average grant-date fair value, granted					$ 11.34		$ 31.03
Total fair value of RSUs vested					$ 1,600,000
RSUs vested					71,000	0	0
Intrinsic value of non-vested RSUs					$ 4,400,000
Restricted stock units awarded			293,980		418,000	0	294,000
Restricted stock units vesting date					Mar. 31, 2017
Stock-based compensation expense					$ 1,400,000	$ 3,800,000	$ 2,300,000
Unrecognized stock-based compensation expense					$ 4,600,000
Estimated weighted-average period					1 year 6 months
Unvested Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation expense					$ 14,400,000
Estimated weighted-average period					2 years 3 months 18 days
Subsequent Event [Member] | Employees Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock available for future issuance under plan								350,000
Maximum [Member] | At-the-Market Offering [Member] | Cantor Fitzgerald & Co [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issuance of common stock value under sales agreement					$ 50,000,000
Performance-based Condition and Service Condition [Member] | Restricted Stock Units [Member] | Celgene [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock units vesting, percentage			25.00%
2004 Stock Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock units vesting period				5 years
Stock options vesting description					Stock options granted generally vest over a period of five years from the date of grant, with 20% of the total grant vesting on the first anniversary of the option vesting commencement date and 1/48 of the remaining grant vesting each month thereafter.
Stock options vesting original months				48 months
Common stock available for future issuance under plan		90,125
Common stock subject to options outstanding					1,745,568
2004 Stock Incentive Plan [Member] | First Anniversary [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options vesting, percentage				20.00%
2013 Equity Incentive Award Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock units vesting period		4 years
Stock options vesting description					Stock options granted generally vest over a period of four years from the date of grant, with 25% of the total grant vesting on the first anniversary of the option vesting commencement date and 1/48th of the original grant vesting each month thereafter for stock options granted upon hiring, and with 1/48th of the total grant vesting each month after the option vesting commencement date for any stock options granted after the hiring date.
Stock options vesting original months		48 months
Common stock available for future issuance under plan		500,000
Exercise price of option, percentage		100.00%
Common stock shares authorized					4,208,201
Common stock subject to options and restricted stock units outstanding					3,154,753
2013 Equity Incentive Award Plan [Member] | Subsequent Event [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock available for future issuance under plan								1,484,583
2013 Equity Incentive Award Plan [Member] | Stock Plan, Annual Increase of Shares 2014 to 2023 [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Increase in common stock		1,500,000
Percentage of common stock outstanding as-converted basis		4.00%
2013 Equity Incentive Award Plan [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Term of options from the grant date		10 years
2013 Equity Incentive Award Plan [Member] | Greater than 10% Stockholder [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock units vesting period		5 years
Exercise price of option, percentage		110.00%
Percentage of incentive stock option granted		10.00%
2013 Equity Incentive Award Plan [Member] | First Anniversary [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options vesting, percentage		25.00%

Stockholder's Equity - Summary

Stockholder's Equity - Summary of Stock Options and RSU Award Activity under 2004 Plan and 2013 Stock Plan (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares Available for Grant, Beginning Balance		145,000	19,000	117,000
Shares Available for Grant, Options authorized		1,205,000	1,194,000	1,176,000
Shares Available for Grant, Options granted		(225,000)	(1,139,000)	(1,027,000)
Shares Available for Grant, Options exercised		0	0	0
Shares Available for Grant, Options forfeited		207,000	63,000	47,000
Shares Available for Grant, Ending Balance		971,000	145,000	19,000
Options Outstanding, Beginning Balance		4,694,000	3,822,000	2,930,000
Options and Awards Outstanding, Options authorized		0	0	0
Options Outstanding, Options granted		225,000	1,139,000	1,027,000
Options Outstanding, Options exercised		(101,000)	(196,000)	(382,000)
Options Outstanding, Options forfeited		(207,000)	(63,000)	(47,000)
Options Outstanding, Ending Balance		4,901,000	4,694,000	3,822,000
Weighted Average Exercise Price per Share, Beginning Balance		$ 14.02	$ 10.84	$ 5.90
Weighted Average Exercise Price per Share, Options authorized		0	0	0
Weighted Average Exercise Price per Share, Options granted		13.19	21.97	22.50
Weighted Average Exercise Price per Share, Options exercised		3.19	3.05	2.83
Weighted Average Exercise Price per Share, Options forfeited		20.34	13.61	22.28
Weighted Average Exercise Price per Share, Ending Balance		$ 13.95	$ 14.02	$ 10.84
Weighted Average Remaining Contractual Life, Outstanding		5 years 1 month 21 days
Weighted Average Remaining Contractual Life, Vested and expected to vest		5 years 1 month 13 days
Weighted Average Remaining Contractual Life, Vested		4 years 3 months 22 days
Aggregate Intrinsic Value, Ending Balance		$ 10,740
Aggregate Intrinsic Value, Vested and expected to vest - Ending Balance		10,723
Aggregate Intrinsic Value, Vested		$ 6,302
Options and Awards Outstanding, Vested and expected to vest - Ending Balance		4,868,000
Options and Awards Outstanding, Vested		2,991,000
Weighted Average Exercise Price per Share, Vested and expected to vest - Ending Balance		$ 13.91
Weighted Average Exercise Price per Share, Vested		$ 11.35
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares Available for Grant of Options and Awards, RSUs granted	(293,980)	(418,000)	0	(294,000)
Shares Available for Grant of Options and Awards, RSU vested		0
Shares Available for Grant of Options and Awards, RSUs forfeited		57,000	8,000
Options and Awards Outstanding, RSUs granted	293,980	418,000	0	294,000
Options and Awards Outstanding, RSU vested		(71,000)	0	0
Options and Awards Outstanding, RSUs forfeited		(57,000)	(8,000)
Weighted Average Exercise Price per Share, RSUs granted		$ 0		$ 0
Weighted Average Exercise Price per Share, RSU vested		0
Weighted Average Exercise Price per Share, RSUs forfeited		$ 0	$ 0

Stockholder's Equity - Schedule

Stockholder's Equity - Schedule of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation	$ 11,131	$ 10,766	$ 6,194
Research and Development [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation	5,892	6,113	3,600
General and Administrative [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation	$ 5,239	$ 4,653	$ 2,594

Stockholder's Equity - Assumpti

Stockholder's Equity - Assumptions Used for Determining Fair Value of Stock Options Using Black-Scholes Valuation Model (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Weighted-average volatility	71.90%	62.60%	66.30%
Weighted-average expected term (years)	5 years 9 months 18 days	6 years 2 months 12 days	6 years 2 months 12 days
Risk-free interest rate	1.50%	2.10%	2.10%

Stockholder's Equity - Assump59

Stockholder's Equity - Assumptions Used for Determining Fair Value of Stock Purchase Rights Granted under Company's ESPP Using Black-Scholes Valuation Model (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average volatility	71.90%	62.60%	66.30%
Weighted-average expected term (years)	5 years 9 months 18 days	6 years 2 months 12 days	6 years 2 months 12 days
Risk-free interest rate	1.50%	2.10%	2.10%
Employees Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average expected term (years)	6 months	6 months	6 months
Employees Stock Purchase Plan [Member] | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average volatility	45.40%	51.10%	65.70%
Risk-free interest rate	0.26%	0.05%	0.05%
Employees Stock Purchase Plan [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average volatility	104.50%	72.50%	115.40%
Risk-free interest rate	0.50%	0.08%	0.08%

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Loss Carryforwards [Line Items]
Income tax provision (benefit)	$ 14,000	$ 20,000	$ (509,000)
Increase in valuation allowance	42,900,000	39,300,000
Alternative minimum tax carryforwards	$ 2,600,000
Tax credit carryforward description	Alternative minimum tax credits have no expiration date.
Impact on income tax provision of unrecognized tax benefits, if recognized	$ 13,100,000	9,000,000
Significant changes in unrecognized tax benefits reasonably possible in next 12 months	0
Accrued interest and penalties related to unrecognized tax benefits	14,000
Liability recognized for interest and penalties	71,000	$ 57,000
Federal [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforward	$ 162,800,000
Operating loss carryforwards, expiration year	2,023
Estimated expire amount of operating loss carryforwards	$ 700,000
Federal [Member] | Orphan drug credit [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards, expiration year	2,034
Aggregate tax credit carryforwards	$ 30,700,000
Federal [Member] | Research and Development Tax Credit Carryforwards [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards, expiration year	2,025
Aggregate tax credit carryforwards	$ 51,500,000
State [Member] | Research and Development Tax Credit Carryforwards [Member]
Operating Loss Carryforwards [Line Items]
Aggregate tax credit carryforwards	$ 18,000,000
Tax credit carryforward description	California research and development credits have no expiration date.
California [Member]
Operating Loss Carryforwards [Line Items]
Estimated expire amount of operating loss carryforwards	$ 700,000
California [Member] | State [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforward	$ 98,400,000
Operating loss carryforwards, expiration year	2,017

Income Taxes - Components of Pr

Income Taxes - Components of Provision (Benefit) for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current:
Federal	$ 13	$ 19	$ (10,841)
State	1	1	1
Total	14	20	(10,840)
Deferred:
Federal			10,331
Total			10,331
Income tax provision (benefit)	$ 14	$ 20	$ (509)

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Statutory Federal Income Tax Rate to Company's Effective Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Tax at statutory federal rate	35.00%	35.00%	35.00%
State tax—net of federal benefit	1.00%	3.00%
Research and development credit	8.00%	9.00%	12.00%
Change in valuation allowance	(42.00%)	(46.00%)	(45.00%)
Other	(2.00%)	(1.00%)	(1.00%)
Income tax (provision) benefit			1.00%

Income Taxes - Schedule of Net

Income Taxes - Schedule of Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Net operating loss carryforwards	$ 58,760	$ 28,833
Accruals	3,520	1,126
Tax credit carryovers	53,047	36,786
Deferred revenue	63,006	70,428
Other	6,668	5,092
Gross deferred tax assets	185,001	142,265
Deferred tax liability		(151)
Valuation allowance	$ (185,001)	$ (142,114)

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 10,022	$ 5,434	$ 4,464
Increase related to current year tax provision	4,238	4,668	1,539
Increase related to prior year tax provision		10
Decrease related to prior year tax provision		(90)	(569)
Balance at end of year	$ 14,260	$ 10,022	$ 5,434

Net Loss per Common Share - Out

Net Loss per Common Share - Outstanding Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Common Share (Detail) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Outstanding shares of common stock equivalents	4,900,321	4,693,757	3,822,012
Options to purchase common stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Outstanding shares of common stock equivalents	4,324,631	4,407,686	3,528,032
Restricted Stock Units [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Outstanding shares of common stock equivalents	575,690	286,071	293,980

Selected Quarterly Financial 66

Selected Quarterly Financial Data - Summary of Selected Quarterly Results from Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement [Abstract]
Total revenue	$ 6,219	$ 5,919	$ 6,665	$ 6,350	$ 6,838	$ 4,687	$ 4,687	$ 9,687	$ 25,153	$ 25,899	$ 39,559
Operating expenses	28,608	31,854	34,481	33,597	31,659	29,248	26,322	24,227	128,540	111,456	90,183
Net loss	$ (22,334)	$ (25,864)	$ (27,691)	$ (27,213)	$ (24,779)	$ (24,479)	$ (21,620)	$ (14,529)	$ (103,102)	$ (85,407)	$ (50,010)
Basic and diluted net loss per common share	$ (0.60)	$ (0.77)	$ (0.91)	$ (0.90)	$ (0.82)	$ (0.81)	$ (0.72)	$ (0.49)	$ (3.14)	$ (2.84)	$ (1.69)