OncoMed Pharmaceuticals 10-Q 7 Aug 14 2014 Q2 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	6 Months Ended
	Jun. 30, 2014	Jul. 31, 2014
Document And Entity Information [Abstract]	'	'
Document Type	'10-Q	'
Amendment Flag	'false	'
Document Period End Date	30-Jun-14	'
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q2	'
Trading Symbol	'OMED	'
Entity Registrant Name	'OncoMed Pharmaceuticals Inc	'
Entity Central Index Key	'0001302573	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Non-accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	29,760,879

Condensed_Balance_Sheets

Condensed Balance Sheets (USD $)	Jun. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current assets:	'	'
Cash and cash equivalents	$23,379	$208,931
Short-term investments	242,969	107,263
Receivables - related parties	23	23
Accounts receivable	48	'
Prepaid and other current assets	2,784	2,527
Total current assets	269,203	318,744
Property and equipment, net	5,168	4,641
Other assets	9,933	10,300
Total assets	284,304	333,685
Current liabilities:	'	'
Accounts payable	3,033	5,706
Income tax payable	'	10,758
Accrued liabilities	12,062	9,860
Current portion of deferred revenue	34,625	35,059
Current portion of deferred rent	651	624
Liability for shares issued with repurchase rights	10	10
Total current liabilities	50,381	62,017
Deferred revenue, less current portion	137,275	148,871
Deferred rent, less current portion	2,809	3,146
Non-current income tax payable	1,528	1,515
Liability for shares issued with repurchase rights, less current portion	8	14
Total liabilities	192,001	215,563
Commitments and contingencies	'	'
Stockholders' equity:	'	'
Preferred stock, value	0	0
Common stock value	30	29
Additional paid-in capital	296,178	292,505
Accumulated other comprehensive income (loss)	-11	14
Accumulated deficit	-203,894	-174,426
Total stockholders' equity	92,303	118,122
Total liabilities and stockholders' equity	$284,304	$333,685

Condensed_Balance_Sheets_Paren

Condensed Balance Sheets (Parenthetical) (USD $)	Jun. 30, 2014	Dec. 31, 2013
Statement Of Financial Position [Abstract]	'	'
Preferred stock, par value	$0.00	$0.00
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	$0.00	$0.00
Common stock, shares authorized	145,000,000	145,000,000
Common stock, shares issued	29,738,391	29,397,964
Common stock, shares outstanding	29,738,391	29,397,964

Condensed_Statements_of_Operat

Condensed Statements of Operations (Unaudited) (USD $)	3 Months Ended		6 Months Ended
In Thousands, except Share data, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Revenue:	'	'	'	'
Collaboration revenue	$6,015	$2,439	$12,030	$4,878
Collaboration revenue - related party	'	493	'	985
Total revenue	6,015	2,932	12,030	5,863
Operating expenses:	'	'	'	'
Research and development	18,167	10,475	34,876	20,051
General and administrative	3,440	1,952	6,653	3,936
Total operating expenses	21,607	12,427	41,529	23,987
Loss from operations	-15,592	-9,495	-29,499	-18,124
Interest and other income (expense), net	-5	-149	31	-118
Net loss	($15,597)	($9,644)	($29,468)	($18,242)
Net loss per common share, basic and diluted	($0.53)	($8.83)	($1)	($16.77)
Shares used to compute net loss per common share, basic and diluted	29,601,010	1,091,782	29,522,556	1,087,863

Condensed_Statements_of_Compre

Condensed Statements of Comprehensive Loss (Unaudited) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Statement Of Comprehensive Loss [Abstract]	'	'	'	'
Net loss	($15,597)	($9,644)	($29,468)	($18,242)
Other comprehensive income (loss):	'	'	'	'
Unrealized gain (loss) on available-for-sale securities, net of tax	18	-5	-25	-1
Total comprehensive loss	($15,579)	($9,649)	($29,493)	($18,243)

Condensed_Statements_of_Cash_F

Condensed Statements of Cash Flows (Unaudited) (USD $)	6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013
Operating activities	'	'
Net loss	($29,468)	($18,242)
Adjustments to reconcile net loss to net cash used in operating activities:	'	'
Depreciation and amortization	685	701
Gain on disposal of equipment	-63	'
Stock-based compensation	2,197	490
Revaluation of convertible preferred stock warrant liability	'	146
Prepaid convertible preferred stock warrant expense	'	1
Amortization of discount on short-term investments	-29	-27
Changes in operating assets and liabilities:	'	'
Receivables - related parties	'	4,000
Accounts receivable	-48	'
Prepaid and other current assets	-257	-101
Other assets	367	-718
Accounts payable	-2,660	-38
Accrued liabilities	2,202	2,211
Deferred revenue	-12,030	2,137
Deferred rent	-310	-254
Income tax payable	-10,758	'
Net cash used in operating activities	-50,172	-9,694
Investing activities	'	'
Purchases of property and equipment	-1,147	-123
Purchases of short-term investments	-282,975	-25,290
Maturities of short-term investments	147,271	35,000
Net cash (used in) provided by investing activities	-136,851	9,587
Financing activities	'	'
Proceeds from issuance of common stock from exercise of options	903	17
Proceeds from issuance of common stock under employee stock purchase plan	568	'
Net cash provided by financing activities	1,471	17
Net (decrease) increase in cash and cash equivalents	-185,552	-90
Cash and cash equivalents at beginning of period	208,931	16,263
Cash and cash equivalents at end of period	$23,379	$16,173

Organization

Organization	6 Months Ended
	Jun. 30, 2014
Accounting Policies [Abstract]	'
Organization	'
	1	Organization
	OncoMed Pharmaceuticals, Inc. (“OncoMed” or the “Company”) is a clinical development-stage biotechnology company focused on discovering and developing first-in-class protein therapeutics targeting cancer stem cells (“CSCs”). The Company was originally incorporated in July 2004 in Delaware. The Company’s operations are based in Redwood City, California and it operates in one segment.
	The Company has five anti-CSC product candidates in clinical development. Additionally, other product candidates are in preclinical development with Investigational New Drug (“IND”) filings planned for as early as late 2014 or 2015. The first candidate, demcizumab, has completed a single-agent Phase Ia safety and dose escalation trial and is currently in Phase Ib combination therapy trials in patients with non-small cell lung cancer (with carboplatin and pemetrexed) and pancreatic cancer (with gemcitabine and Abraxane®) and a Phase Ib/II trial combining demcizumab with paclitaxel in ovarian cancer. The second candidate, tarextumab (anti-Notch2/3, OMP-59R5), completed a Phase Ia safety and dose escalation trial and is in the Phase II portion of a Phase Ib/II trial in pancreatic cancer (with gemcitabine and Abraxane®) (see Note 8. Subsequent Events) and in a second Phase Ib/II trial in small cell lung cancer (with etoposide and platinum chemotherapy). The third candidate, vantictumab (OMP-18R5), is in a single-agent Phase Ia trial and three separate Phase Ib combination trials, one trial each in patients with breast cancer (with paclitaxel), pancreatic cancer (with gemcitabine and Abraxane®) and non-small cell lung cancer (with docetaxel). The fourth candidate, ipafricept (Fzd8-Fc, OMP-54F28), is in a single-agent Phase Ia safety and dose escalation trial in solid tumor malignancies, and is currently in three separate Phase Ib combination trials, one trial each in patients with ovarian cancer (with carboplatin and paclitaxel), pancreatic cancer (with gemcitabine and Abraxane®) and hepatocellular carcinoma (with sorafenib). The Company’s Phase I clinical trials for both vantictumab and ipafricept have been placed on partial clinical hold by the U.S. Food and Drug Administration (“FDA”) following a voluntary halt of the trials by the Company. The fifth candidate, anti-Notch1 (OMP-52M51), is in two single-agent Phase Ia safety and dose escalation trials in hematologic and solid tumor malignancies.
	Initial Public Offering
	On July 17, 2013, the Company’s registration statement on Form S-1 (File No. 333-181331) relating to the initial public offering (the “IPO”) of its common stock was declared effective by the SEC. The IPO closed on July 23, 2013 at which time the Company sold 5,520,000 shares of its common stock, which included 720,000 shares of common stock purchased by the underwriters upon the full exercise of their option to purchase additional shares of common stock to cover over-allotments. The Company received net cash proceeds of $82.7 million from the IPO, net of underwriting discounts and commissions and expenses paid by the Company.
	On July 23, 2013, prior to the closing of the IPO, all outstanding shares of convertible preferred stock converted into 21,180,280 shares of common stock with the related carrying value of $182.8 million reclassified to common stock and additional paid-in capital. In addition, all convertible preferred stock warrants were also thereby converted into common stock warrants. Additionally, all shares of Class B common stock were converted into Class A common stock, and the Class A common stock was redesignated “common stock”.

Summary_of_Significant_Account

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2014
Accounting Policies [Abstract]	'
Summary of Significant Accounting Policies	'
	2	Summary of Significant Accounting Policies
	Basis of Presentation
	The accompanying unaudited condensed financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and following the requirements of the Securities and Exchange Commission (the “SEC”) for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP can be condensed or omitted. These financial statements have been prepared on the same basis as the Company’s annual financial statements and, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments, that are necessary for a fair statement of the Company’s financial information. These interim results are not necessarily indicative of the results to be expected for the year ending December 31, 2014 or for any other interim period or for any other future year. The balance sheet as of December 31, 2013 has been derived from audited financial statements at that date but does not include all of the information required by U.S. GAAP for complete financial statements.
	The accompanying condensed financial statements and related financial information should be read in conjunction with the audited financial statements and the related notes thereto contained in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2013, filed with the SEC on March 18, 2014.
	Use of Estimates
	The preparation of financial statements in conformity with accounting principles generally accepted in the United States 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.
	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. 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 option fees 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 collaborative research and development revenue accounted for 10% or more of total revenues were as follows:
			Three Months Ended		Six Months Ended
			June 30,		June 30,
			2014	2013	2014	2013
	GlaxoSmithKline LLC (“GSK”)		*	17%	*	17%
	Bayer Pharma AG (“Bayer”)		41%	83%	41%	83%
	Celgene Corporation (“Celgene”)		54%	—	54%	—
	*	Less than 10%.
	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 share equivalents outstanding for the period determined using the treasury-stock method. For purposes of this calculation, potentially dilutive securities consisting of convertible preferred stock, common stock subject to repurchase, stock options and warrants 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.
	Recent Adopted Accounting Pronouncements
	In June 2014, the Financial Accounting Standards Board (“FASB”) issued final guidance that a performance target that affects vesting of a share-based payment and that could be achieved after the requisite service period is a performance condition under Accounting Standards Codification (“ASC”) 718, Compensation — Stock Compensation. As a result, the target is not reflected in the estimation of the award’s grant date fair value. Compensation cost for such an award would be recognized over the required service period, if it is probable that the performance condition will be achieved. The guidance is effective for all entities for annual periods beginning after December 15, 2015 and interim periods within those annual periods. The guidance should be applied on a prospective basis to awards that are granted or modified on or after the effective date. The Company does not believe the adoption of this guidance will have a material impact on its financial statement.
	In May 2014, the FASB and the International Accounting Standards Board issued Accounting Standards Update (“ASU”) No. 2014-09 (Topic 606)—Revenue from Contracts with Customers (“ASU 2014-09”). This ASU affects any entity that either enters into contracts with customers to transfer goods and services or enters into contracts for the transfer of nonfinancial assets. This ASU will supersede the revenue recognition requirements in Topic 605, and most industry specific guidance. It also supersedes some cost guidance included in Subtopic 605-35, Revenue Recognition-Construction-Type and Production-Type Contracts. The standard’s core principle is that a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. In doing so, companies will need to use more judgment and make more estimates than under today’s guidance. These may include identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. ASU 2014-09 is effective for the Company for annual periods beginning after December 15, 2016, including interim periods within that period. Early adoption is not permitted under U.S. GAAP. The Company is currently evaluating the impact of adoption on its financial statements.

Cash_Equivalents_and_ShortTerm

Cash Equivalents and Short-Term Investments	6 Months Ended
	Jun. 30, 2014
Cash And Cash Equivalents [Abstract]	'
Cash Equivalents and Short-Term Investments	'
	3	Cash Equivalents and Short-Term Investments
	The fair value of securities, not including cash, at June 30, 2014 was as follows (in thousands):
			June 30, 2014
			Amortized		Gross Unrealized					Fair Value
			Cost		Gains		Losses
	Money market funds		$	8,282	$	—	$	—		$	8,282
	U.S. treasury bills			242,980		33		(44	)		242,969
	Total available-for-sale securities		$	251,262	$	33	$	(44	)	$	251,251
	Classified as:
	Cash equivalents									$	8,282
	Short-term investments										242,969
	Total cash equivalents and investments									$	251,251
	As of June 30, 2014, the Company had a total of $266.3 million in cash, cash equivalents, and short-term investments, which includes $15.0 million in cash and $251.3 million in cash equivalents and short-term investments.
	The fair value of securities, not including cash, at December 31, 2013 was as follows (in thousands):
			December 31, 2013
			Amortized		Gross Unrealized					Fair Value
			Cost		Gains		Losses
	Money market funds		$	7,980	$	—	$	—		$	7,980
	U.S. treasury bills			267,242		14		—			267,256
	Total available-for-sale securities		$	275,222	$	14	$	—		$	275,236
	Classified as:
	Cash equivalents									$	167,973
	Short-term investments										107,263
	Total cash equivalents and investments									$	275,236
	All available-for-sale securities held as of June 30, 2014 and December 31, 2013 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	6 Months Ended
	Jun. 30, 2014
Fair Value Disclosures [Abstract]	'
Fair Value Measurements	'
	4	Fair Value Measurements
	The Company records its financial assets and liabilities at fair value. The carrying amounts of certain of the Company’s financial instruments, including cash and cash equivalents, short-term investments, accounts receivable and accounts payable, approximate their fair value due to their short maturities. The accounting guidance for fair value provides a framework for measuring fair value, clarifies the definition of fair value, and expands disclosures regarding fair value measurements. 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):
			June 30, 2014
			Level 1		Level 2		Level 3		Total
	Assets:
	Money market funds		$	8,282	$	—	$	—	$	8,282
	U.S. treasury bills			—		242,969		—		242,969
	Total		$	8,282	$	242,969	$	—	$	251,251
			31-Dec-13
			Level 1		Level 2		Level 3		Total
	Assets:
	Money market funds		$	7,980	$	—	$	—	$	7,980
	U.S. treasury bills			—		267,256		—		267,256
	Total		$	7,980	$	267,256	$	—	$	275,236
	Where quoted prices are available in an active market, securities are classified as Level 1. The Company classifies money market funds 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.

Collaborations

Collaborations	6 Months Ended
	Jun. 30, 2014
Organization Consolidation And Presentation Of Financial Statements [Abstract]	'
Collaborations	'
	5	Collaborations
	The Company has recognized the following revenues from its collaboration agreements with Celgene, GSK and Bayer during the three and six months ended June 30, 2014 and 2013 (in thousands):
			Three Months Ended				Six Months Ended
			June 30,				June 30,
			2014		2013		2014		2013
	GSK: Recognition of upfront payments		$	312	$	493	$	624	$	985
	Bayer: Recognition of upfront payments			2,439		2,439		4,878		4,878
	Celgene: Recognition of upfront payments			3,264		—		6,528		—
	Total collaboration related revenue		$	6,015	$	2,932	$	12,030	$	5,863
	GSK Strategic Alliance
	In October 2012, the Company received a $3.0 million payment from GSK upon the initiation of the Phase Ib portion of the tarextumab (anti-Notch2/3, OMP-59R5) program which was considered as an advance payment on a future substantive milestone. In June 2013, the Company also received an $8.0 million advance payment from GSK pursuant to the terms of its tarextumab program. The total of $11.0 million has been recorded as deferred revenue and will be recognized as collaboration revenue upon the achievement of the underlying substantive milestone. See Note 8. Subsequent Events.
	As of June 30, 2014, the Company was eligible to receive in its collaboration with GSK up to $81.0 million in future development milestone payments prior to the completion of certain Phase II proof-of-concept (“POC”) clinical trials. These remaining potential development milestones include up to $5.0 million for the advancement into specified clinical testing related to the anti-Notch1 (OMP-52M51) program, up to $16.0 million for the start of certain Phase II clinical trials, including a $5.0 million bonus payment, and up to $60.0 million if GSK exercises its options for the anti-Notch1 and tarextumab programs, including a $10.0 million bonus payment. GSK has the option to license the anti-Notch1 program as early as the end of Phase Ia or both programs at Phase II POC, and will be responsible for all further development and commercialization following such option exercise. If GSK successfully develops and commercializes both candidates for more than one indication, the Company could receive contingent consideration payments of up to $309.0 million for the achievement of regulatory events and up to $280.0 million upon the achievement of certain levels of worldwide net sales, for a total of $670.0 million of potential future payments. In addition, the Company can earn royalty payments on all future collaboration product sales, if any. As all contingent consideration is based solely on the performance of GSK, 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 GSK.
	As of December 31, 2013, GSK was no longer considered a related party due to an equity placement from Celgene pursuant to the collaboration agreement the Company entered into with Celgene in December 2013 that reduced GSK’s ownership of the Company’s voting common stock to below 10% of the Company’s total outstanding stock. Previously, GSK was deemed a related party by ownership of more than 10% of the voting common stock of the Company. Accordingly, related party transactions were reported as receivable—related party in the Company’s balance sheets and collaboration revenue—related party in the Company’s statements of operations as of June 30, 2013.
	Bayer Strategic Alliance
	As of June 30, 2014, 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 $24.0 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 (OMP-21M18), anti-DLL4/anti-VEGF bispecific antibody (OMP-305B83), biologic therapeutics directed to targets in the RSPO-LGR signaling pathway, 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 completion of certain clinical trials, provided that such option exercise occurs within the contractual option period of 12 years (“Option Period”). The Company at its option may enter into co-commercialization and co-development agreements for five of the six biologic programs. During the Option Period, 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 biologic therapeutic products prior to Celgene’s exercise of its option. 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 within the Option Period.
	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 from Celgene. 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 option fees 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 payment upon the achievement of certain pre-determined safety criteria in Phase II clinical trials with respect to demcizumab, (2) $505.0 million for products in the anti-DLL4/anti-VEGF bispecific program, (3) up to $442.8 million for each of the four products achieving regulatory approval that are directed to targets in each of the RSPO-LGR signaling pathway and the undisclosed pathway programs for which Celgene exercises its option, and (4) $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 Celgene fails to exercise any of its options within the Option Period. 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 within the Option Period, the Company retains worldwide rights to such program(s), except that if Celgene exercises its option to obtain a license for either the demcizumab program or the anti-DLL4/anti-VEGF bispecific 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 option fees 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.
	As of June 30, 2014, the Company was eligible to receive in its collaboration with Celgene up to $90.0 million in future development milestones across all programs under the collaboration, prior to the point that Celgene exercises its options. The Company is also eligible to receive up to $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 $2.8 billion for the achievement of regulatory events (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.
	For additional information about the Company’s collaborations with GSK, Bayer and Celgene, including the upfront payments received under those collaborations, see Note 10 to the audited financial statements included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2013, filed with SEC on March 18, 2014.

Equity_Plans

Equity Plans	6 Months Ended
	Jun. 30, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'
Equity Plans	'
	6	Equity Plans
	Equity Incentive Award and Stock Incentive Plans
	As of June 30, 2014, a total of 1,768,645 shares of common stock have been authorized under the 2013 Equity Incentive Award Plan (the “2013 Plan”), including the additional 1,175,918 shares of common stock that became available for future issuance under the 2013 Plan as of January 1, 2014 as a result of an annual automatic increase provision in the 2013 Plan. As of June 30, 2014, a total of 940,548 shares are subject to options outstanding under the 2013 Plan. There are 2,161,301 shares subject to options outstanding under 2004 Stock Incentive Plan (the “2004 Plan”) as of June 30, 2014, 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.
	The following table summarizes activity under 2004 Plan and 2013 Plan, including grants to nonemployees and restricted stock units (“RSUs”) granted:
	(In thousands)		Shares			Options and
			Available for			Awards
			Grant of			Outstanding
			Options and
			Awards
	Balances at December 31, 2013			117			2,930
	Additional shares authorized			1,176			—
	Options granted			(202	)		202
	Options exercised			—			(299	)
	Options cancelled			25			(25	)
	RSUs granted			(294	)		294
	Balances at June 30, 2014			822			3,102
	The weighted-average grant-date estimated fair value of options and RSUs granted during the six months ended June 30, 2014 was $17.96 per share and $31.03 per share, respectively.
	Liability for Shares with Repurchase Rights
	At June 30, 2014 and December 31, 2013, there were 4,036 and 5,088 shares of common stock, respectively, subject to the Company’s right of repurchase at price of $4.56 per share. At June 30, 2014 and December 31, 2013, the Company recorded $18,000 and $23,000, respectively, as liabilities associated with shares issued with repurchase rights.
	Employee Stock Purchase Plan
	As of June 30, 2014, a total of 593,979 shares of common stock have been authorized and 553,229 shares of common stock are available for future issuance under the Company’s Employee Stock Purchase Plan (the “ESPP”). This authorized number includes the additional 293,979 shares of common stock that became available for future issuance under the ESPP as of January 1, 2014 as a result of an annual automatic increase provision in the ESPP. 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.
	During the six months ended June 30, 2014, the Company issued 40,750 shares under the ESPP. The Company used the following assumptions to estimate the fair value of the ESPP offered for the six months ended June 30, 2014: expected term of 0.5 years, weighted-average volatility from 65.7% to 115.4%, risk-free interest rate from 0.05% to 0.08% and expected dividend yield of zero.
	Restricted Stock Units
	In March 2014, the Company awarded 293,980 RSUs under the 2013 Plan. Each vested RSU represents the right to receive one share of common stock. The fair value of the RSU awards was calculated based on the NASDAQ quoted stock price on the date of the grant with the expense being recognized over the vesting period. The RSUs are generally scheduled to vest at the end of three years at March 31, 2017. However, the vesting will be accelerated to 25% of the awarded RSUs upon the payment by Celgene of a designated milestone payment related to Phase II clinical trials of demcizumab. The stock-based compensation expense for these RSUs is being amortized on the straight-line basis over the three-year vesting period. The company continues to assess at each reporting date whether achievement of any performance condition is probable and would begin recognizing compensation costs based on the accelerated vesting if and when achievement of the performance condition becomes probable. There were no RSUs awarded during the three months ended June 30, 2014. The Company has recognized the stock-based compensation expense of $745,000 and $803,000 related to these RSUs for the three and six months ended June 30, 2014, respectively.
	Stock-Based Compensation
	The following table presents stock-based compensation expense recognized for stock options, RSUs and the ESPP in the Company’s statements of operations (in thousands):
			Three Months Ended						Six Months Ended
			June 30,						June 30,
			2014			2013			2014			2013
	Research and development		$	977		$	134		$	1,388		$	274
	General and administrative			530			131			809			216
	Total		$	1,507		$	265		$	2,197		$	490
	As of June 30, 2014, the Company had $8.0 million and $8.3 million of unrecognized compensation expense related to unvested stock options and RSUs, respectively, which are expected to be recognized over an estimated weighted-average period of 2.67 years and 2.75 years, respectively.
	The estimated grant date fair value of employee stock options was calculated using the Black-Scholes valuation model, based on the following assumptions:
			Three Months Ended						Six Months Ended
			June 30,						June 30,
			2014			2013			2014			2013
	Weighted-average volatility			69.45	%		—	%		69.65	%		68.5	%
	Weighted-average expected term (years)			6.2			—			6.2			6.2
	Risk-free interest rate			2.22	%		—	%		2.23	%		1.4	%
	Expected dividend yield			—			—			—			—

Net_Loss_per_Common_Share

Net Loss per Common Share	6 Months Ended
	Jun. 30, 2014
Earnings Per Share [Abstract]	'
Net Loss per Common Share	'
	7	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:
			June 30,
			2014		2013
	Convertible preferred stock			—		21,180,280
	Options to purchase common stock			2,807,869		2,544,101
	RSUs			293,980		—
	Warrants to purchase convertible preferred stock			—		38,210
				3,101,849		23,762,591

Subsequent_Events

Subsequent Events	6 Months Ended
	Jun. 30, 2014
Subsequent Events [Abstract]	'
Subsequent Events	'
	8	Subsequent Events
	In July 2014, the Company began dosing patients in the randomized, placebo-controlled Phase II portion of its clinical trial of tarextumab (anti-Notch2/3, OMP-59R5) in pancreatic cancer. As such, the Company recognized $11.0 million of milestone revenue, which had been previously deferred, related to first patient enrollment in the Phase II portion of its tarextumab clinical trial under its agreement with GSK.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2014
Accounting Policies [Abstract]	'
Basis of Presentation	'
	Basis of Presentation
	The accompanying unaudited condensed financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and following the requirements of the Securities and Exchange Commission (the “SEC”) for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP can be condensed or omitted. These financial statements have been prepared on the same basis as the Company’s annual financial statements and, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments, that are necessary for a fair statement of the Company’s financial information. These interim results are not necessarily indicative of the results to be expected for the year ending December 31, 2014 or for any other interim period or for any other future year. The balance sheet as of December 31, 2013 has been derived from audited financial statements at that date but does not include all of the information required by U.S. GAAP for complete financial statements.
	The accompanying condensed financial statements and related financial information should be read in conjunction with the audited financial statements and the related notes thereto contained in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2013, filed with the SEC on March 18, 2014.
Use of Estimates	'
	Use of Estimates
	The preparation of financial statements in conformity with accounting principles generally accepted in the United States 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.
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. 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 option fees 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 collaborative research and development revenue accounted for 10% or more of total revenues were as follows:
			Three Months Ended			Six Months Ended
			June 30,			June 30,
			2014		2013	2014	2013
	GlaxoSmithKline LLC (“GSK”)		*		17%	*	17%
	Bayer Pharma AG (“Bayer”)		41%		83%	41%	83%
	Celgene Corporation (“Celgene”)		54%		—	54%	—
	*	Less than 10%.
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 share equivalents outstanding for the period determined using the treasury-stock method. For purposes of this calculation, potentially dilutive securities consisting of convertible preferred stock, common stock subject to repurchase, stock options and warrants 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.
Recent Adopted Accounting Pronouncements	'
	Recent Adopted Accounting Pronouncements
	In June 2014, the Financial Accounting Standards Board (“FASB”) issued final guidance that a performance target that affects vesting of a share-based payment and that could be achieved after the requisite service period is a performance condition under Accounting Standards Codification (“ASC”) 718, Compensation — Stock Compensation. As a result, the target is not reflected in the estimation of the award’s grant date fair value. Compensation cost for such an award would be recognized over the required service period, if it is probable that the performance condition will be achieved. The guidance is effective for all entities for annual periods beginning after December 15, 2015 and interim periods within those annual periods. The guidance should be applied on a prospective basis to awards that are granted or modified on or after the effective date. The Company does not believe the adoption of this guidance will have a material impact on its financial statement.
	In May 2014, the FASB and the International Accounting Standards Board issued Accounting Standards Update (“ASU”) No. 2014-09 (Topic 606)—Revenue from Contracts with Customers (“ASU 2014-09”). This ASU affects any entity that either enters into contracts with customers to transfer goods and services or enters into contracts for the transfer of nonfinancial assets. This ASU will supersede the revenue recognition requirements in Topic 605, and most industry specific guidance. It also supersedes some cost guidance included in Subtopic 605-35, Revenue Recognition-Construction-Type and Production-Type Contracts. The standard’s core principle is that a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. In doing so, companies will need to use more judgment and make more estimates than under today’s guidance. These may include identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. ASU 2014-09 is effective for the Company for annual periods beginning after December 15, 2016, including interim periods within that period. Early adoption is not permitted under U.S. GAAP. The Company is currently evaluating the impact of adoption on its financial statements.
Fair Value Measurement Policy	'
	The Company records its financial assets and liabilities at fair value. The carrying amounts of certain of the Company’s financial instruments, including cash and cash equivalents, short-term investments, accounts receivable and accounts payable, approximate their fair value due to their short maturities. The accounting guidance for fair value provides a framework for measuring fair value, clarifies the definition of fair value, and expands disclosures regarding fair value measurements. 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.
Fair Value of Financial Instruments Policy	'
	Where quoted prices are available in an active market, securities are classified as Level 1. The Company classifies money market funds 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.

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2014
Accounting Policies [Abstract]	'
Schedule of Collaborative Research and Development Revenue	'
	Customers whose collaborative research and development revenue accounted for 10% or more of total revenues were as follows:
			Three Months Ended		Six Months Ended
			June 30,		June 30,
			2014	2013	2014	2013
	GlaxoSmithKline LLC (“GSK”)		*	17%	*	17%
	Bayer Pharma AG (“Bayer”)		41%	83%	41%	83%
	Celgene Corporation (“Celgene”)		54%	—	54%	—
	*	Less than 10%.

Cash_Equivalents_and_ShortTerm1

Cash Equivalents and Short-Term Investments (Tables)	6 Months Ended
	Jun. 30, 2014
Cash And Cash Equivalents [Abstract]	'
Schedule of Fair Value of Securities, Not Including Cash	'
	The fair value of securities, not including cash, at June 30, 2014 was as follows (in thousands):
		June 30, 2014
		Amortized		Gross Unrealized					Fair Value
		Cost		Gains		Losses
	Money market funds	$	8,282	$	—	$	—		$	8,282
	U.S. treasury bills		242,980		33		(44	)		242,969
	Total available-for-sale securities	$	251,262	$	33	$	(44	)	$	251,251
	Classified as:
	Cash equivalents								$	8,282
	Short-term investments									242,969
	Total cash equivalents and investments								$	251,251
	As of June 30, 2014, the Company had a total of $266.3 million in cash, cash equivalents, and short-term investments, which includes $15.0 million in cash and $251.3 million in cash equivalents and short-term investments.
	The fair value of securities, not including cash, at December 31, 2013 was as follows (in thousands):
		December 31, 2013
		Amortized		Gross Unrealized					Fair Value
		Cost		Gains		Losses
	Money market funds	$	7,980	$	—	$	—		$	7,980
	U.S. treasury bills		267,242		14		—			267,256
	Total available-for-sale securities	$	275,222	$	14	$	—		$	275,236
	Classified as:
	Cash equivalents								$	167,973
	Short-term investments									107,263
	Total cash equivalents and investments								$	275,236

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2014
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):
		June 30, 2014
		Level 1		Level 2		Level 3		Total
	Assets:
	Money market funds	$	8,282	$	—	$	—	$	8,282
	U.S. treasury bills		—		242,969		—		242,969
	Total	$	8,282	$	242,969	$	—	$	251,251
		31-Dec-13
		Level 1		Level 2		Level 3		Total
	Assets:
	Money market funds	$	7,980	$	—	$	—	$	7,980
	U.S. treasury bills		—		267,256		—		267,256
	Total	$	7,980	$	267,256	$	—	$	275,236

Collaborations_Tables

Collaborations (Tables)	6 Months Ended
	Jun. 30, 2014
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 with Celgene, GSK and Bayer during the three and six months ended June 30, 2014 and 2013 (in thousands):
		Three Months Ended				Six Months Ended
		June 30,				June 30,
		2014		2013		2014		2013
	GSK: Recognition of upfront payments	$	312	$	493	$	624	$	985
	Bayer: Recognition of upfront payments		2,439		2,439		4,878		4,878
	Celgene: Recognition of upfront payments		3,264		—		6,528		—
	Total collaboration related revenue	$	6,015	$	2,932	$	12,030	$	5,863

Equity_Plans_Tables

Equity Plans (Tables)	6 Months Ended
	Jun. 30, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'
Summary of Activity under 2004 Plan and 2013 Stock Plan	'
	The following table summarizes activity under 2004 Plan and 2013 Plan, including grants to nonemployees and restricted stock units (“RSUs”) granted:
	(In thousands)	Shares			Options and
		Available for			Awards
		Grant of			Outstanding
		Options and
		Awards
	Balances at December 31, 2013		117			2,930
	Additional shares authorized		1,176			—
	Options granted		(202	)		202
	Options exercised		—			(299	)
	Options cancelled		25			(25	)
	RSUs granted		(294	)		294
	Balances at June 30, 2014		822			3,102
Schedule of Stock-Based Compensation Expense	'
	The following table presents stock-based compensation expense recognized for stock options, RSUs and the ESPP in the Company’s statements of operations (in thousands):
		Three Months Ended						Six Months Ended
		June 30,						June 30,
		2014			2013			2014			2013
	Research and development	$	977		$	134		$	1,388		$	274
	General and administrative		530			131			809			216
	Total	$	1,507		$	265		$	2,197		$	490
Assumptions Used for Determining Fair Value of Stock Options Using Black-Scholes Valuation Model	'
	The estimated grant date fair value of employee stock options was calculated using the Black-Scholes valuation model, based on the following assumptions:
		Three Months Ended						Six Months Ended
		June 30,						June 30,
		2014			2013			2014			2013
	Weighted-average volatility		69.45	%		—	%		69.65	%		68.5	%
	Weighted-average expected term (years)		6.2			—			6.2			6.2
	Risk-free interest rate		2.22	%		—	%		2.23	%		1.4	%
	Expected dividend yield		—			—			—			—

Net_Loss_per_Common_Share_Tabl

Net Loss per Common Share (Tables)	6 Months Ended
	Jun. 30, 2014
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:
		June 30,
		2014		2013
	Convertible preferred stock		—		21,180,280
	Options to purchase common stock		2,807,869		2,544,101
	RSUs		293,980		—
	Warrants to purchase convertible preferred stock		—		38,210
			3,101,849		23,762,591

Organization_Additional_Inform

Organization - Additional Information (Detail) (USD $)	6 Months Ended		0 Months Ended		0 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jul. 23, 2013	Jul. 23, 2013	Jul. 23, 2013
	Segment		Initial Public Offering [Member]	Initial Public Offering [Member]	Initial Public Offering [Member]
					Underwriters [Member]
Class of Stock [Line Items]	'	'	'	'	'
Number of operating segment	1	'	'	'	'
Incorporation date	31-Jul-04	'	'	'	'
Initial Public Offering effective date	17-Jul-13	'	'	'	'
Initial Public Offering closure date	23-Jul-13	'	'	'	'
Common stock, shares issued	'	'	5,520,000	'	720,000
Cash proceeds from IPO, net of underwriting discounts and commissions and expenses	'	'	$82,700,000	'	'
Conversion of preferred stock into common stock, shares	'	'	'	21,180,280	'
Conversion of preferred stock into common stock, carrying value	$0	$0	'	$182,800,000	'

Summary_of_Significant_Account3

Summary of Significant Accounting Policies - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2014
Revenue [Member] | Customer Concentration [Member] | Minimum [Member]	'
Schedule of Available-for-sale Securities [Line Items]	'
Concentration risk percentage of revenue represented by major customers	10.00%
Cash and Cash Equivalents [Member]	'
Schedule of Available-for-sale Securities [Line Items]	'
Short-term investments maturities, maximum	'90 days
Short-Term Investments [Member]	'
Schedule of Available-for-sale Securities [Line Items]	'
Short-term investments maturities, maximum	'365 days
Short-term investments maturities, minimum	'90 days

Summary_of_Significant_Account4

Summary of Significant Accounting Policies - Schedule of Collaborative Research and Development Revenue (Detail) (Revenue [Member], Customer Concentration [Member])	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
GSK [Member]	'	'	'	'
Concentration Risk [Line Items]	'	'	'	'
Collaborative research and development revenue, Percentage	'	17.00%	'	17.00%
Bayer [Member]	'	'	'	'
Concentration Risk [Line Items]	'	'	'	'
Collaborative research and development revenue, Percentage	41.00%	83.00%	41.00%	83.00%
Celgene [Member]	'	'	'	'
Concentration Risk [Line Items]	'	'	'	'
Collaborative research and development revenue, Percentage	54.00%	'	54.00%	'

Summary_of_Significant_Account5

Summary of Significant Accounting Policies - Schedule of Collaborative Research and Development Revenue (Parenthetical) (Detail) (Minimum [Member], Customer Concentration [Member], Revenue [Member])	6 Months Ended
	Jun. 30, 2014
Minimum [Member] | Customer Concentration [Member] | Revenue [Member]	'
Concentration Risk [Line Items]	'
Concentration risk percentage of revenue represented by major customers	10.00%

Cash_Equivalents_and_ShortTerm2

Cash Equivalents and Short-Term Investments - Schedule of Fair Value of Securities, Not Including Cash (Detail) (USD $)	Jun. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Fair Value, Option, Quantitative Disclosures [Line Items]	'	'
Amortized Cost	$251,262	$275,222
Gross Unrealized Gains	33	14
Gross Unrealized Losses	-44	'
Fair Value	251,251	275,236
Cash equivalents	8,282	167,973
Short-term investments	242,969	107,263
Total cash equivalents and investments	251,251	275,236
Money Market Funds [Member]	'	'
Fair Value, Option, Quantitative Disclosures [Line Items]	'	'
Amortized Cost	8,282	7,980
Fair Value	8,282	7,980
U.S. Treasury Bills [Member]	'	'
Fair Value, Option, Quantitative Disclosures [Line Items]	'	'
Amortized Cost	242,980	267,242
Gross Unrealized Gains	33	14
Gross Unrealized Losses	-44	'
Fair Value	$242,969	$267,256

Cash_Equivalents_and_ShortTerm3

Cash Equivalents and Short-Term Investments - Additional Information (Detail) (USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]	'	'
Total cash, cash equivalents, and short-term investments	$266,300,000	'
Cash	15,000,000	'
Cash equivalents and short-term investments	251,251,000	275,236,000
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_Summar

Fair Value Measurements - Summary of Company's Financial Assets and Liabilities Subject to Fair Value Measurements on Recurring Basis (Detail) (USD $)	Jun. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Assets:	'	'
Assets fair value disclosure	$251,251	$275,236
Money Market Funds [Member]	'	'
Assets:	'	'
Assets fair value disclosure	8,282	7,980
U.S. Treasury Bills [Member]	'	'
Assets:	'	'
Assets fair value disclosure	242,969	267,256
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]	'	'
Assets:	'	'
Assets fair value disclosure	8,282	7,980
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]	'	'
Assets:	'	'
Assets fair value disclosure	242,969	267,256
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | Level 1 [Member]	'	'
Assets:	'	'
Assets fair value disclosure	8,282	7,980
Fair Value, Measurements, Recurring [Member] | U.S. Treasury Bills [Member] | Level 2 [Member]	'	'
Assets:	'	'
Assets fair value disclosure	$242,969	$267,256

Fair_Value_Measurements_Additi

Fair Value Measurements - Additional Information (Detail) (USD $)	Jun. 30, 2014
Fair Value Disclosures [Abstract]	'
Transfers between Level 1 and Level 2	$0

Collaborations_Company_Recogni

Collaborations - Company Recognized Revenues from Collaboration Agreements (Detail) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'	'	'	'
Collaboration revenue	$6,015	$2,439	$12,030	$4,878
Total revenue	6,015	2,932	12,030	5,863
Collaborative Arrangement [Member]	'	'	'	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'	'	'	'
Total revenue	6,015	2,932	12,030	5,863
Collaborative Arrangement [Member] | GSK [Member] | Recognition of Upfront Payments [Member]	'	'	'	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'	'	'	'
Collaboration revenue	312	493	624	985
Collaborative Arrangement [Member] | Bayer [Member] | Recognition of Upfront Payments [Member]	'	'	'	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'	'	'	'
Collaboration revenue	2,439	2,439	4,878	4,878
Collaborative Arrangement [Member] | Celgene [Member] | Recognition of Upfront Payments [Member]	'	'	'	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'	'	'	'
Collaboration revenue	$3,264	'	$6,528	'

Collaborations_GSK_Strategic_A

Collaborations - GSK Strategic Alliance - Additional Information (Detail) (GSK [Member], USD $)	6 Months Ended					6 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Oct. 31, 2012	Dec. 31, 2013	Dec. 31, 2013	Jun. 30, 2014	Jun. 30, 2014
				Maximum [Member]	Minimum [Member]	Anti-Notch 1 [Member]	Tarextumab Anti-Notch 2/3, OMP-59R5 [Member]
Related Party Transaction [Line Items]	'	'	'	'	'	'	'
Deferred revenue	$11	$8	$3	'	'	'	'
Development milestone payments	81	'	'	'	'	'	'
Remaining potential development milestones	5	'	'	'	'	'	'
Remaining potential development milestone payment	'	'	'	'	'	16	'
Bonus payment	'	'	'	'	'	5	10
Milestones on completion of exercise options	'	'	'	'	'	'	60
Contingent consideration payments	309	'	'	'	'	'	'
Contingent consideration payments for achievement of worldwide net sales	280	'	'	'	'	'	'
Potential future payments	$670	'	'	'	'	'	'
Deemed ownership percentage of related party	'	'	'	10.00%	10.00%	'	'

Collaborations_Bayer_Strategic

Collaborations - Bayer Strategic Alliance - Additional Information (Detail) (Bayer [Member], USD $)	6 Months Ended
In Millions, unless otherwise specified	Jun. 30, 2014
Related Party Transaction [Line Items]	'
Future development milestone payments	$10
Achievement of Regulatory Events [Member]	'
Related Party Transaction [Line Items]	'
Contingent consideration payments for regulatory events	185
Achievement of Specified Future Product Sales [Member]	'
Related Party Transaction [Line Items]	'
Contingent consideration payments for regulatory events	1,000
Biologic Product [Member]	'
Related Party Transaction [Line Items]	'
Future development milestone payments	55
Biologic Product [Member] | Achievement of Regulatory Events [Member]	'
Related Party Transaction [Line Items]	'
Contingent consideration payments for regulatory events	135
Biologic Product [Member] | Achievement of Specified Future Product Sales [Member]	'
Related Party Transaction [Line Items]	'
Contingent consideration payments for regulatory events	862.5
Small Molecules [Member]	'
Related Party Transaction [Line Items]	'
Future development milestone payments	24
Small Molecules [Member] | Achievement of Regulatory Events [Member]	'
Related Party Transaction [Line Items]	'
Contingent consideration payments for regulatory events	50
Small Molecules [Member] | Achievement of Specified Future Product Sales [Member]	'
Related Party Transaction [Line Items]	'
Contingent consideration payments for regulatory events	$140

Collaborations_Celgene_Strateg

Collaborations - Celgene Strategic Alliance - Additional Information (Detail) (Celgene [Member], USD $)	6 Months Ended
In Millions, except Share data, unless otherwise specified	Jun. 30, 2014
	Program
Related Party Transaction [Line Items]	'
Collaboration and Option Agreement date	'December 2013
Contractual option exercised period of clinical trials	'12 years
Number of biologic programs	6
Number of biological program for which company can enter into co-commercialization and co-development agreements	5
Collaboration agreement extension period	'2 years
Upfront cash payment received	$155
Issuance of common stock in connection with research and collaboration agreement	1,470,588
Common stock price per share	$15.13
Proceeds from issuance of common stock	22.2
Premium on closing price of common stock value	1.7
Common stock, fair market value	20.5
Profits and losses sharing percentage	50.00%
Initial arrangement consideration	156.7
Estimated revenue recognition period	'12 years
Future development milestone payments	90
Achievement of Regulatory Events [Member]	'
Related Party Transaction [Line Items]	'
Additional contingent consideration for regulatory events	2,800
Demcizumab Program [Member]	'
Related Party Transaction [Line Items]	'
Regulatory and commercial milestones payments	791
Bispecific Antibody Program [Member]	'
Related Party Transaction [Line Items]	'
Regulatory and commercial milestones payments	505
Undisclosed Pathway Programs [Member]	'
Related Party Transaction [Line Items]	'
Regulatory and commercial milestones payments	442.8
Small Molecules [Member]	'
Related Party Transaction [Line Items]	'
Regulatory and commercial milestones payments	107
Small Molecules [Member] | Achievement of Regulatory Events [Member]	'
Related Party Transaction [Line Items]	'
Additional contingent consideration for regulatory events	95
Biologic and Small Molecule Therapeutic Programs [Member]	'
Related Party Transaction [Line Items]	'
Future development milestone payments	240
Biologic Product [Member] | Achievement of Regulatory Events [Member]	'
Related Party Transaction [Line Items]	'
Additional contingent consideration for regulatory events	$2,700

Equity_Plans_Additional_Inform

Equity Plans - Additional Information (Detail) (USD $)

3 Months Ended

6 Months Ended

12 Months Ended

6 Months Ended

6 Months Ended

1 Months Ended

3 Months Ended

6 Months Ended

Jun. 30, 2014

Jun. 30, 2013

Jun. 30, 2014

Jun. 30, 2013

Dec. 31, 2013

Jun. 30, 2014

Jun. 30, 2014

Jan. 02, 2014

Jun. 30, 2014

Jan. 02, 2014

Jun. 30, 2014

Jun. 30, 2014

Jun. 30, 2014

Mar. 31, 2014

Jun. 30, 2014

Jun. 30, 2014

2013 Equity Incentive Award Plan [Member]

2004 Stock Incentive Plan [Member]

2004 Stock Incentive Plan [Member]

Employees Stock Purchase Plan [Member]

Employees Stock Purchase Plan [Member]

Employees Stock Purchase Plan [Member]

Employees Stock Purchase Plan [Member]

Unvested Stock Options [Member]

Restricted Stock Units [Member]

Restricted Stock Units [Member]

Restricted Stock Units [Member]

Minimum [Member]

Maximum [Member]

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

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Common stock shares authorized

'

'

'

'

'

1,768,645

'

'

593,979

'

'

'

'

'

'

'

Common stock subject to options outstanding

'

'

'

'

'

940,548

2,161,301

'

'

'

'

'

'

'

'

'

Common stock available for future issuance under plan

'

'

'

'

'

'

'

1,175,918

553,229

293,979

'

'

'

'

'

'

Weighted-average grant-date fair value, granted

'

'

$17.96

'

'

'

'

'

'

'

'

'

'

'

'

$31.03

Repurchase of common stock outstanding

4,036

'

4,036

'

5,088

'

'

'

'

'

'

'

'

'

'

'

Repurchase prices of common stock

'

'

$4.56

'

$4.56

'

'

'

'

'

'

'

'

'

'

'

Liability for shares issued with repurchase rights

$18,000

'

$18,000

'

$23,000

'

'

'

'

'

'

'

'

'

'

'

Common stock purchased at discount through payroll deductions

'

'

'

'

'

'

'

'

15.00%

'

'

'

'

'

'

'

Shares purchased lower of the fair market value

'

'

'

'

'

'

'

'

85.00%

'

'

'

'

'

'

'

Employee stock purchase plan, offering period

'

'

'

'

'

'

'

'

'6 months

'

'

'

'

'

'

'

Common stock issued to employees under ESPP

'

'

'

'

'

'

'

'

40,750

'

'

'

'

'

'

'

Estimated fair value expected term

'6 years 2 months 12 days

'

'6 years 2 months 12 days

'6 years 2 months 12 days

'

'

'

'

'6 months

'

'

'

'

'

'

'

Estimated fair value weighted-average volatility rate

69.45%

'

69.65%

68.50%

'

'

'

'

'

'

65.70%

115.40%

'

'

'

'

Estimated fair value risk-free interest rate

2.22%

'

2.23%

1.40%

'

'

'

'

'

'

0.05%

0.08%

'

'

'

'

Estimated fair value expected dividend yield

'

'

'

'

'

'

'

'

0.00%

'

'

'

'

'

'

'

Restricted stock units awarded

'

'

294,000

'

'

'

'

'

'

'

'

'

'

293,980

0

'

Restricted stock units vesting period

'

'

'

'

'

'

'

'

'

'

'

'

'

'3 years

'

'

Restricted stock units vesting date

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

31-Mar-17

Restricted stock units vesting, percentage

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

25.00%

Amortization of stock based compensation expense on straight-line basis

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'3 years

Stock-based compensation expense

1,507,000

265,000

2,197,000

490,000

'

'

'

'

'

'

'

'

'

'

745,000

803,000

Unrecognized compensation expense

'

'

'

'

'

'

'

'

'

'

'

'

$8,000,000

'

$8,300,000

$8,300,000

Estimated weighted-average period

'

'

'

'

'

'

'

'

'

'

'

'

'2 years 8 months 1 day

'

'

'2 years 9 months

Equity_Plans_Summary_of_Activi

Equity Plans - Summary of Activity under 2004 Plan and 2013 Stock Plan (Detail)	6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'
Shares Available for Grant of Options and Awards, Beginning Balance	117
Shares Available for Grant of Options and Awards, Additional Options authorized	1,176
Shares Available for Grant of Options and Awards, Options granted	-202
Shares Available for Grant of Options and Awards, Options exercised	'
Shares Available for Grant of Options and Awards, Options cancelled	25
Shares Available for Grant of Options and Awards, RSUs granted	-294
Shares Available for Grant of Options and Awards, Ending Balance	822
Options and Awards Outstanding, Beginning Balance	2,930
Options and Awards Outstanding, Additional Options authorized	'
Options and Awards Outstanding, Options granted	202
Options and Awards Outstanding, Options exercised	-299
Options and Awards Outstanding, Options cancelled	-25
Options and Awards Outstanding, RSUs granted	294
Options and Awards Outstanding, Ending Balance	3,102

Equity_Plans_Schedule_of_Stock

Equity Plans - Schedule of Stock-Based Compensation Expense (Detail) (USD $)	3 Months Ended		6 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'	'	'
Stock-based compensation	$1,507	$265	$2,197	$490
Research and Development [Member]	'	'	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'	'	'
Stock-based compensation	977	134	1,388	274
General and Administrative [Member]	'	'	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'	'	'
Stock-based compensation	$530	$131	$809	$216

Equity_Plans_Assumptions_Used_

Equity Plans - Assumptions Used for Determining Fair Value of Stock Options Using Black-Scholes Valuation Model (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'	'	'	'
Weighted-average volatility	69.45%	'	69.65%	68.50%
Weighted-average expected term (years)	'6 years 2 months 12 days	'	'6 years 2 months 12 days	'6 years 2 months 12 days
Risk-free interest rate	2.22%	'	2.23%	1.40%
Expected dividend yield	'	'	'	'

Net_Loss_per_Common_Share_Outs

Net Loss per Common Share - Outstanding Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Common Share (Detail)	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'
Outstanding shares of common stock equivalents	3,101,849	23,762,591
Options to Purchase Common Stock [Member]	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'
Outstanding shares of common stock equivalents	2,807,869	2,544,101
Restricted Stock Units [Member]	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'
Outstanding shares of common stock equivalents	293,980	'
Convertible Preferred Stock [Member]	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'
Outstanding shares of common stock equivalents	'	21,180,280
Convertible Preferred Stock [Member] | Warrants [Member]	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'
Outstanding shares of common stock equivalents	'	38,210

Subsequent_Events_Additional_I

Subsequent Events - Additional Information (Detail) (GSK [Member], Subsequent Event [Member], USD $)	1 Months Ended
In Millions, unless otherwise specified	Jul. 31, 2014
GSK [Member] | Subsequent Event [Member]	'
Subsequent Event [Line Items]	'
Milestone revenue recognized	$11