Five Prime Therapeutics (FPRX) 10-Q 12 Nov 14 2014 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2014	Oct. 31, 2014
Document And Entity Information [Abstract]	'	'
Document Type	'10-Q	'
Amendment Flag	'false	'
Document Period End Date	30-Sep-14	'
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q3	'
Trading Symbol	'FPRX	'
Entity Registrant Name	'FIVE PRIME THERAPEUTICS INC	'
Entity Central Index Key	'0001175505	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Non-accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	21,550,672

Condensed_Balance_Sheets

Condensed Balance Sheets (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current assets:	'	'
Cash and cash equivalents	$13,128	$8,161
Marketable securities	116,854	67,561
Receivable from collaborative partners	91	296
Prepaid and other current assets	1,775	1,640
Total current assets	131,848	77,658
Property and equipment, net	3,979	3,744
Other long-term assets	431	389
Total assets	136,258	81,791
Current liabilities:	'	'
Accounts payable	672	348
Accrued personnel-related expenses	3,106	2,957
Other accrued liabilities	2,235	2,056
Deferred revenue, current portion	11,676	7,913
Deferred rent, current portion	611	549
Total current liabilities	18,300	13,823
Deferred revenue, long-term portion	20,920	7,123
Deferred rent, long-term portion	1,672	2,146
Other long-term liabilities	504	673
Commitments	'	'
Stockholders' equity:	'	'
Common stock	22	17
Preferred stock	'	'
Additional paid-in capital	271,952	209,580
Accumulated other comprehensive income	60	3
Accumulated deficit	-177,172	-151,574
Total stockholders' equity	94,862	58,026
Total liabilities and stockholders' equity	$136,258	$81,791

Condensed_Statements_of_Operat

Condensed Statements of Operations (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Statement [Abstract]	'	'	'	'
Collaboration revenue	$6,059	$3,482	$14,586	$10,006
Operating expenses:	'	'	'	'
Research and development	9,803	8,193	30,602	24,708
General and administrative	3,360	2,607	9,664	7,385
Total operating expenses	13,163	10,800	40,266	32,093
Loss from operations	-7,104	-7,318	-25,680	-22,087
Interest income	57	7	148	35
Other income (expense), net	-41	77	-66	497
Net loss	($7,088)	($7,234)	($25,598)	($21,555)
Basic and diluted net loss per common share	($0.33)	($2.74)	($1.24)	($12.60)
Shares used to compute basic and diluted net loss per common share	21,521	2,637	20,619	1,711

Condensed_Statements_of_Compre

Condensed Statements of Comprehensive Loss (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement Of Income And Comprehensive Income [Abstract]	'	'	'	'
Net loss	($7,088)	($7,234)	($25,598)	($21,555)
Other comprehensive income (loss):	'	'	'	'
Net unrealized gain (loss) on marketable securities	19	'	60	-6
Comprehensive loss	($7,069)	($7,234)	($25,538)	($21,561)

Condensed_Statement_of_Cash_Fl

Condensed Statement of Cash Flows (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Operating activities	'	'
Net loss	($25,598)	($21,555)
Adjustments to reconcile net loss to net cash used in operating activities:	'	'
Depreciation and amortization	1,154	1,288
Loss on disposal of property and equipment	41	'
Stock-based compensation expense	2,230	1,554
Amortization of premium on marketable securities	1,075	272
Revaluation of preferred stock warrant liability	'	-500
Changes in operating assets and liabilities:	'	'
Receivable from collaborative partners	205	14
Prepaid, other current assets, and other long-term assets	-539	-2
Accounts payable	324	467
Accrued personnel-related expenses	149	-154
Deferred revenue	17,560	2,677
Deferred rent	-412	189
Other accrued liabilities and other long-term liabilities	373	18
Net cash used in operating activities	-3,438	-15,732
Investing activities	'	'
Purchases of marketable securities	-121,016	-12,078
Maturities of marketable securities	70,705	29,435
Purchases of property and equipment	-1,430	-633
Net cash (used in) provided by investing activities	-51,741	16,724
Financing activities	'	'
Proceeds from public offering of common stock, net	40,099	64,887
Proceeds from the sale of common stock to collaborative partner	18,629	'
Proceeds from issuance of common stock under equity incentive plans	1,418	387
Payments under capital lease obligation	'	-9
Net cash provided by financing activities	60,146	65,265
Net increase in cash and cash equivalents	4,967	66,257
Cash and cash equivalents at beginning of period	8,161	11,391
Cash and cash equivalents at end of period	13,128	77,648
Supplemental schedule of noncash financing activities	'	'
Accrued and deferred offering costs	'	$1,026

Description_of_Business

Description of Business	9 Months Ended
	Sep. 30, 2014
Accounting Policies [Abstract]	'
Description of Business	'
	1	Description of Business
	Five Prime Therapeutics, Inc. (we, us, our or the Company) is a clinical-stage biotechnology company focused on discovering and developing novel protein therapeutics. Protein therapeutics are antibodies or drugs developed from extracellular proteins or protein fragments that block disease processes, including cancer and inflammatory diseases. We were incorporated in December 2001 in Delaware. Our operations are based in South San Francisco, California and we operate in one segment.
	Unaudited Interim Financial Information
	The accompanying financial information as of September 30, 2014 is unaudited. The Condensed Financial Statements included in this report reflect all adjustments (consisting only of normal recurring adjustments) that our management considers necessary for the fair statement of the results of operations for the interim periods covered and of the financial condition of the Company at the date of the interim balance sheet. The December 31, 2013 Condensed Balance Sheet was derived from audited financial statements, but does not include all disclosures required by generally accepted accounting principles in the United States of America, or GAAP. The results for interim periods are not necessarily indicative of the results for the entire year or any other interim period. The accompanying Condensed Financial Statements and related financial information should be read in conjunction with the audited financial statements and the related notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2013 filed with the U.S. Securities and Exchange Commission.
	Follow-on Public Offering
	In February 2014, we completed a public offering of 3,450,000 shares of our common stock, or our Follow-on Public Offering, which included shares we issued pursuant to our underwriters’ exercise of their over-allotment option. We received net proceeds of $40.1 million, after underwriting discounts, commissions and offering expenses, from the Follow-on Public Offering.

Summary_of_Significant_Account

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2014
Accounting Policies [Abstract]	'
Summary of Significant Accounting Policies	'
	2	Summary of Significant Accounting Policies
	Use of Estimates
	The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions about future events that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements as well as reported amounts of revenue and expenses during the reporting period. Actual results could differ materially from those estimates.
	Reclassifications
	We have reclassified certain prior period amounts to conform to the current period presentation. We reclassified certain liabilities, primarily those related to unbilled receipts, from accounts payable to other accrued liabilities on our balance sheets and made related conforming reclassifications on our statements of cash flows.
	Fair Value of Financial Instruments
	We determine the fair value of financial and nonfinancial assets and liabilities using the fair value hierarchy, which describes three levels of inputs that may be used to measure fair value, as follows:
	Level 1—Quoted prices in active markets for identical assets or liabilities;
	Level 2—Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities, quoted prices for identical or similar assets or liabilities 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; and
	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.
	We determine the fair value of Level 1 assets using quoted prices in active markets for identical assets. We review trading activity and pricing for Level 2 investments as of each measurement date. Level 2 inputs, obtained from various third-party data providers, represent quoted prices for similar assets in active markets and were derived from observable market data, or, if not directly observable, were derived from or corroborated by other observable market data.
	In certain cases where there is limited activity or less transparency around inputs to valuation, we classify securities as Level 3 within the valuation hierarchy.
	The following table summarizes, for assets recorded at fair value, the respective fair values and the classifications by level of input within the fair value hierarchy defined above (in thousands):
		30-Sep-14
				BASIS OF FAIR VALUE
				MEASUREMENTS
		TOTAL		LEVEL 1		LEVEL 2		LEVEL 3
	Assets
	Money market funds	$	8,925	$	8,925	$	—	$	—
	U.S. Treasury securities		106,330		106,330		—		—
	U.S. government agency securities		10,524		—		10,524		—
	Total cash equivalents and marketable securities	$	125,779	$	115,255	$	10,524	$	—
		31-Dec-13
				BASIS OF FAIR VALUE
				MEASUREMENTS
		TOTAL		LEVEL 1		LEVEL 2		LEVEL 3
	Assets
	Money market funds	$	6,456	$	6,456	$	—	$	—
	U.S. Treasury securities		18,852		18,852		—		—
	U.S. government agency securities		48,709		—		48,709		—
	Total cash equivalents and marketable securities	$	74,017	$	25,308	$	48,709	$	—
	Net Loss Per Share of Common Stock
	We compute basic net loss per common share by dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period. We did not include potentially dilutive securities consisting of stock options, preferred stock warrants, common stock warrants and convertible preferred stock in the diluted net loss per common share calculations for all periods presented because the inclusion of such shares would have had an antidilutive effect. The convertible preferred stock contained certain participation rights.
	We excluded the following securities (in thousands) from the calculation of diluted net loss per share as the effect would have been antidilutive:
		Three Months Ended				Nine Months Ended
		September 30,				September 30,
		2014		2013		2014		2013
	Convertible preferred stock		—		9,174		—		9,675
	Options to purchase common stock		2,404		2,235		2,253		2,235
	Warrants to purchase preferred stock		—		75		—		79
	Warrants to purchase common stock		—		2		—		2
			2,404		11,486		2,253		11,991
	Recently Issued Accounting Standards
	In May 2014, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, No. 2014-09, “Revenue from Contracts with Customers.” ASU 2014-09 supersedes the revenue recognition requirements in “Topic 605, Revenue Recognition” and requires entities to recognize revenue in a way that depicts the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. ASU 2014-09 is effective retrospectively for annual or interim reporting periods beginning after December 15, 2016, with early application not permitted. We are currently evaluating the effect the adoption of ASU 2014-09 will have on our financial statements.

Cash_Equivalents_and_Marketabl

Cash Equivalents and Marketable Securities	9 Months Ended
	Sep. 30, 2014
Cash And Cash Equivalents [Abstract]	'
Cash Equivalents and Marketable Securities	'
	3	Cash Equivalents and Marketable Securities
	The following is a summary of our cash equivalents and marketable securities (in thousands):
		30-Sep-14
		AMORTIZED			UNREALIZED		UNREALIZED			ESTIMATED
		COST BASIS			GAINS		LOSSES			FAIR VALUE
		(unaudited)
	Money market funds	$	8,925		$	—	$	—		$	8,925
	U.S. Treasury securities		106,274			57		(1	)		106,330
	U.S. government agency securities		10,520			4		—			10,524
			125,719			61		(1	)		125,779
	Less: cash equivalents		(8,925	)		—		—			(8,925	)
	Total marketable securities	$	116,794		$	61	$	(1	)	$	116,854
		31-Dec-13
		AMORTIZED			UNREALIZED		UNREALIZED			ESTIMATED
		COST BASIS			GAINS		LOSSES			FAIR VALUE
	Money market funds	$	6,456		$	—	$	—		$	6,456
	U.S. Treasury securities		18,848			4		—			18,852
	U.S. government agency securities		48,709			3		(3	)		48,709
			74,013			7		(3	)		74,017
	Less: cash equivalents		(6,456	)		—		—			(6,456	)
	Total marketable securities	$	67,557		$	7	$	(3	)	$	67,561
	As of September 30, 2014, the amortized cost and estimated fair value of our available-for-sale securities by contractual maturity are shown below (in thousands):
		Amortized			Estimated
		Cost			Fair Value
		(unaudited)
	Debt securities maturing:
	In one year or less	$	96,527		$	96,574
	In one to two years		29,192			29,205
	Total marketable securities	$	125,719		$	125,779
	We determined that the gross unrealized losses of $1,000 on our marketable securities as of September 30, 2014 were temporary in nature. We currently do not intend to sell these securities prior to maturity and do not consider these investments to be other-than-temporarily impaired at September 30, 2014. There were no sales of available-for-sale securities in any of the periods presented.

Equity_Incentive_Plans

Equity Incentive Plans	9 Months Ended
	Sep. 30, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'
Equity Incentive Plans	'
	4	Equity Incentive Plans
	The following table summarizes option activity under our stock plans and related information:
		OPTIONS OUTSTANDING
					WEIGHTED			WEIGHTED
					AVERAGE			AVERAGE
		NUMBER OF			EXERCISE PRICE			REMAINING
		SHARES			PER SHARE			CONTRACTUAL TERM
	Balance at December 31, 2013		2,236,997		$	6.09
	Options granted		780,195		$	11.62
	Options exercised		(188,439	)	$	5.29
	Options forfeited		(59,623	)	$	7.63
	Balance at September 30, 2014		2,769,130		$	7.67
	Options exercisable		1,440,891		$	6.03			6
	As of September 30, 2014, there were 3,393,083 shares of common stock available for future issuance under our 2013 Omnibus Incentive Plan.
	Stock-Based Compensation
	We calculate employee stock-based compensation expense based on awards ultimately expected to vest reduced by estimated forfeitures. We estimate forfeitures at the time of grant and revise forfeitures, if necessary, in subsequent periods if actual forfeitures differ from those estimates. Total stock-based compensation expense recognized was as follows (in thousands):
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
		2014			2013			2014			2013
	Research and development	$	383		$	261		$	1,112		$	661
	General and administrative		471			258			1,118			893
	Total	$	854		$	519		$	2,230		$	1,554
	We estimated the fair value of each stock option using the Black-Scholes option-pricing model based on the date of grant of such stock option with the following assumptions:
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
		2014			2013			2014			2013
	Expected term (years)	5.4-6.7			5.3-6.1			5.3-6.7			5.0-6.1
	Expected volatility		85	%		85	%		85	%		85	%
	Risk-free interest rate	1.7-2.0			1.4-1.6%			1.6-2.0			0.8-1.6%
	Expected dividend yield		0	%		0	%		0	%		0	%
	As of September 30, 2014, we had $8.4 million of total unrecognized compensation expense related to nonvested employee and director stock options that we expect to recognize over a weighted-average period of 3.1 years.

Collaborative_Research_and_Dev

Collaborative Research and Development Agreements	9 Months Ended
	Sep. 30, 2014
Organization Consolidation And Presentation Of Financial Statements [Abstract]	'
Collaborative Research and Development Agreements	'
	5	Collaborative Research and Development Agreements
	Bristol-Myers Squibb Company
	On March 14, 2014, we entered into a research collaboration and license agreement, referred to as the immuno-oncology collaboration, with Bristol-Myers Squibb Company, or BMS, to carry out a research program to (i) discover novel interacting proteins in two undisclosed immune checkpoint pathways, which we refer to as the checkpoint pathways, using our target discovery platform; (ii) further the understanding of target biology with respect to targets in these checkpoint pathways; and (iii) discover and pre-clinically develop compounds suitable for development for human therapeutic uses against targets in these checkpoint pathways. Under the immuno-oncology collaboration, we granted BMS an exclusive, worldwide license to research, develop and commercialize products directed towards certain targets in the checkpoint pathways. BMS will have an option to take exclusive licenses to additional targets we may identify in these checkpoint pathways during the course of the immuno-oncology collaboration. We received an upfront payment of $20.0 million from BMS in April 2014 in connection with our entry into the immuno-oncology collaboration and expect to receive $9.5 million in research funding over the course of the three-year research term based on the research activities currently planned under the research plan. BMS may extend the research term for two additional one-year periods on a year-by-year basis, during which extensions we would be obligated to perform additional services as agreed to with BMS and BMS would be obligated to pay us research funding with respect to such services.
	We applied the Financial Accounting Standards Board Accounting Standards Update, or ASU, No. 2009-13, Multiple-Deliverable Revenue Arrangements, in evaluating the appropriate accounting for the immuno-oncology collaboration. In accordance with this guidance, we concluded that we should account for the immuno-oncology collaboration as a single unit of accounting and recognize the immuno-oncology collaboration consideration in the same manner as the final deliverable, which is research service. The $20.0 million upfront payment was recorded as deferred revenue and is being recognized over the five-year research period under the collaboration. In addition, BMS agreed to pay us $9.5 million of research funding over the initial three-year research program term. We received $2.3 million of research funding during the nine months ended September 30, 2014 related to research we performed under the immuno-oncology collaboration.
	We are eligible to receive certain contingent payments with respect to each target subject to the immuno-oncology collaboration and royalties on sales of products related to such targets, if any.
	In accordance with ASU No. 2010-17, Milestone Method of Revenue Recognition, we determined that the remaining contingent payments under the immuno-oncology collaboration do not constitute milestone payments and will not be accounted for under the milestone method of revenue recognition. The events leading to these payments under the collaboration do not meet the definition of a milestone under ASU 2010-17 because the achievement of these events solely depends on BMS’s performance. Any revenue from these contingent payments would be subject to an allocation of arrangement consideration and would be recognized over any remaining period of performance obligations, if any, relating to the collaboration. If we have no remaining performance obligations under the immuno-oncology collaboration at the time the contingent payment is triggered, we would recognize the contingent payment as revenue in full upon the triggering event.
	In connection with the immuno-oncology collaboration, BMS purchased 994,352 shares of our common stock at a price per share of $21.16, for an aggregate purchase price of $21.0 million. We determined that the purchase price of $21.16 per share exceeded the fair value of our common stock by $2.4 million and, therefore, recorded the $2.4 million as deferred revenue, which we will recognize in the same manner as the $20.0 million up-front payment.
	During the three and nine months ended September 30, 2014, we recognized $2.0 million and $4.1 million, respectively, of revenue under the immuno-oncology collaboration. As of September 30, 2014, we had deferred revenue relating to the immuno-oncology collaboration of $20.6 million.
	The immuno-oncology collaboration will terminate upon the expiration of all payment obligations under the collaboration. In addition, BMS may terminate the immuno-oncology collaboration in its entirety or on a collaboration target-by-collaboration target basis at any time with advance written notice and either party may terminate the collaboration in its entirety or on a collaboration target-by-collaboration target basis with written notice for the other party’s material breach if such party fails to cure the breach or immediately upon certain insolvency events.
	GlaxoSmithKline
	Respiratory Diseases Discovery Collaboration
	In April 2014, we amended our research collaboration and license agreement, referred to as the respiratory diseases collaboration, with Glaxo Group Limited, or GSK, that we originally entered into in April 2012 to identify new therapeutic approaches to treat refractory asthma and chronic obstructive pulmonary disease function. Pursuant to the respiratory diseases collaboration, GSK has an option to elect to include additional screening assays under the research plan. The amendment allows GSK to terminate any additional screening assay it elects under the research plan within nine months of so electing, which termination right lapsed unexercised in October 2014. Concurrent with the amendment, GSK exercised its option and expanded the research plan to include two additional screening assays. In connection with GSK’s exercise of its option, we are entitled to receive up to $1.0 million in additional research funding in 16 equal quarterly payments for each additional screening assay, for a total of up to $2.0 million in additional research funding for both additional screening assays, of which we have received $0.5 million as of September 30, 2014.

Description_of_Business_Polici

Description of Business (Policies)	9 Months Ended
	Sep. 30, 2014
Accounting Policies [Abstract]	'
Unaudited Interim Financial Information	'
	Unaudited Interim Financial Information
	The accompanying financial information as of September 30, 2014 is unaudited. The Condensed Financial Statements included in this report reflect all adjustments (consisting only of normal recurring adjustments) that our management considers necessary for the fair statement of the results of operations for the interim periods covered and of the financial condition of the Company at the date of the interim balance sheet. The December 31, 2013 Condensed Balance Sheet was derived from audited financial statements, but does not include all disclosures required by generally accepted accounting principles in the United States of America, or GAAP. The results for interim periods are not necessarily indicative of the results for the entire year or any other interim period. The accompanying Condensed Financial Statements and related financial information should be read in conjunction with the audited financial statements and the related notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2013 filed with the U.S. Securities and Exchange Commission.
Use of Estimates	'
	Use of Estimates
	The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions about future events that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements as well as reported amounts of revenue and expenses during the reporting period. Actual results could differ materially from those estimates.
Reclassifications	'
	Reclassifications
	We have reclassified certain prior period amounts to conform to the current period presentation. We reclassified certain liabilities, primarily those related to unbilled receipts, from accounts payable to other accrued liabilities on our balance sheets and made related conforming reclassifications on our statements of cash flows.
Fair Value of Financial Instruments	'
	Fair Value of Financial Instruments
	We determine the fair value of financial and nonfinancial assets and liabilities using the fair value hierarchy, which describes three levels of inputs that may be used to measure fair value, as follows:
	Level 1—Quoted prices in active markets for identical assets or liabilities;
	Level 2—Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities, quoted prices for identical or similar assets or liabilities 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; and
	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.
	We determine the fair value of Level 1 assets using quoted prices in active markets for identical assets. We review trading activity and pricing for Level 2 investments as of each measurement date. Level 2 inputs, obtained from various third-party data providers, represent quoted prices for similar assets in active markets and were derived from observable market data, or, if not directly observable, were derived from or corroborated by other observable market data.
	In certain cases where there is limited activity or less transparency around inputs to valuation, we classify securities as Level 3 within the valuation hierarchy.
	The following table summarizes, for assets recorded at fair value, the respective fair values and the classifications by level of input within the fair value hierarchy defined above (in thousands):
		30-Sep-14
				BASIS OF FAIR VALUE
				MEASUREMENTS
		TOTAL		LEVEL 1		LEVEL 2		LEVEL 3
	Assets
	Money market funds	$	8,925	$	8,925	$	—	$	—
	U.S. Treasury securities		106,330		106,330		—		—
	U.S. government agency securities		10,524		—		10,524		—
	Total cash equivalents and marketable securities	$	125,779	$	115,255	$	10,524	$	—
		31-Dec-13
				BASIS OF FAIR VALUE
				MEASUREMENTS
		TOTAL		LEVEL 1		LEVEL 2		LEVEL 3
	Assets
	Money market funds	$	6,456	$	6,456	$	—	$	—
	U.S. Treasury securities		18,852		18,852		—		—
	U.S. government agency securities		48,709		—		48,709		—
	Total cash equivalents and marketable securities	$	74,017	$	25,308	$	48,709	$	—
Net Loss Per Share of Common Stock	'
	Net Loss Per Share of Common Stock
	We compute basic net loss per common share by dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period. We did not include potentially dilutive securities consisting of stock options, preferred stock warrants, common stock warrants and convertible preferred stock in the diluted net loss per common share calculations for all periods presented because the inclusion of such shares would have had an antidilutive effect. The convertible preferred stock contained certain participation rights.
	We excluded the following securities (in thousands) from the calculation of diluted net loss per share as the effect would have been antidilutive:
		Three Months Ended				Nine Months Ended
		September 30,				September 30,
		2014		2013		2014		2013
	Convertible preferred stock		—		9,174		—		9,675
	Options to purchase common stock		2,404		2,235		2,253		2,235
	Warrants to purchase preferred stock		—		75		—		79
	Warrants to purchase common stock		—		2		—		2
			2,404		11,486		2,253		11,991
Recently Issued Accounting Standards	'
	Recently Issued Accounting Standards
	In May 2014, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, No. 2014-09, “Revenue from Contracts with Customers.” ASU 2014-09 supersedes the revenue recognition requirements in “Topic 605, Revenue Recognition” and requires entities to recognize revenue in a way that depicts the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. ASU 2014-09 is effective retrospectively for annual or interim reporting periods beginning after December 15, 2016, with early application not permitted. We are currently evaluating the effect the adoption of ASU 2014-09 will have on our financial statements.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2014
Accounting Policies [Abstract]	'
Summary of Assets Recorded at Fair Value	'
	The following table summarizes, for assets recorded at fair value, the respective fair values and the classifications by level of input within the fair value hierarchy defined above (in thousands):
		30-Sep-14
				BASIS OF FAIR VALUE
				MEASUREMENTS
		TOTAL		LEVEL 1		LEVEL 2		LEVEL 3
	Assets
	Money market funds	$	8,925	$	8,925	$	—	$	—
	U.S. Treasury securities		106,330		106,330		—		—
	U.S. government agency securities		10,524		—		10,524		—
	Total cash equivalents and marketable securities	$	125,779	$	115,255	$	10,524	$	—
		31-Dec-13
				BASIS OF FAIR VALUE
				MEASUREMENTS
		TOTAL		LEVEL 1		LEVEL 2		LEVEL 3
	Assets
	Money market funds	$	6,456	$	6,456	$	—	$	—
	U.S. Treasury securities		18,852		18,852		—		—
	U.S. government agency securities		48,709		—		48,709		—
	Total cash equivalents and marketable securities	$	74,017	$	25,308	$	48,709	$	—
Securities Excluded from Calculation of Diluted Net Loss per Share	'
	We excluded the following securities (in thousands) from the calculation of diluted net loss per share as the effect would have been antidilutive:
		Three Months Ended				Nine Months Ended
		September 30,				September 30,
		2014		2013		2014		2013
	Convertible preferred stock		—		9,174		—		9,675
	Options to purchase common stock		2,404		2,235		2,253		2,235
	Warrants to purchase preferred stock		—		75		—		79
	Warrants to purchase common stock		—		2		—		2
			2,404		11,486		2,253		11,991

Cash_Equivalents_and_Marketabl1

Cash Equivalents and Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2014
Cash And Cash Equivalents [Abstract]	'
Summary of Cash Equivalents and Marketable Securities	'
	The following is a summary of our cash equivalents and marketable securities (in thousands):
		30-Sep-14
		AMORTIZED			UNREALIZED		UNREALIZED			ESTIMATED
		COST BASIS			GAINS		LOSSES			FAIR VALUE
		(unaudited)
	Money market funds	$	8,925		$	—	$	—		$	8,925
	U.S. Treasury securities		106,274			57		(1	)		106,330
	U.S. government agency securities		10,520			4		—			10,524
			125,719			61		(1	)		125,779
	Less: cash equivalents		(8,925	)		—		—			(8,925	)
	Total marketable securities	$	116,794		$	61	$	(1	)	$	116,854
		31-Dec-13
		AMORTIZED			UNREALIZED		UNREALIZED			ESTIMATED
		COST BASIS			GAINS		LOSSES			FAIR VALUE
	Money market funds	$	6,456		$	—	$	—		$	6,456
	U.S. Treasury securities		18,848			4		—			18,852
	U.S. government agency securities		48,709			3		(3	)		48,709
			74,013			7		(3	)		74,017
	Less: cash equivalents		(6,456	)		—		—			(6,456	)
	Total marketable securities	$	67,557		$	7	$	(3	)	$	67,561
Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale Securities by Contractual Maturity	'
	As of September 30, 2014, the amortized cost and estimated fair value of our available-for-sale securities by contractual maturity are shown below (in thousands):
		Amortized			Estimated
		Cost			Fair Value
		(unaudited)
	Debt securities maturing:
	In one year or less	$	96,527		$	96,574
	In one to two years		29,192			29,205
	Total marketable securities	$	125,719		$	125,779

Equity_Incentive_Plans_Tables

Equity Incentive Plans (Tables)	9 Months Ended
	Sep. 30, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'
Schedule of Option Activity under Stock Plans and Related Information	'
	The following table summarizes option activity under our stock plans and related information:
		OPTIONS OUTSTANDING
					WEIGHTED			WEIGHTED
					AVERAGE			AVERAGE
		NUMBER OF			EXERCISE PRICE			REMAINING
		SHARES			PER SHARE			CONTRACTUAL TERM
	Balance at December 31, 2013		2,236,997		$	6.09
	Options granted		780,195		$	11.62
	Options exercised		(188,439	)	$	5.29
	Options forfeited		(59,623	)	$	7.63
	Balance at September 30, 2014		2,769,130		$	7.67
	Options exercisable		1,440,891		$	6.03			6
Schedule of Stock-Based Compensation Expenses Recognized	'
	Total stock-based compensation expense recognized was as follows (in thousands):
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
		2014			2013			2014			2013
	Research and development	$	383		$	261		$	1,112		$	661
	General and administrative		471			258			1,118			893
	Total	$	854		$	519		$	2,230		$	1,554
Schedule of Stock Option Assumptions	'
	We estimated the fair value of each stock option using the Black-Scholes option-pricing model based on the date of grant of such stock option with the following assumptions:
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
		2014			2013			2014			2013
	Expected term (years)	5.4-6.7			5.3-6.1			5.3-6.7			5.0-6.1
	Expected volatility		85	%		85	%		85	%		85	%
	Risk-free interest rate	1.7-2.0			1.4-1.6%			1.6-2.0			0.8-1.6%
	Expected dividend yield		0	%		0	%		0	%		0	%

Description_of_Business_Additi

Description of Business - Additional Information (Detail) (USD $)	1 Months Ended	9 Months Ended
In Thousands, except Share data, unless otherwise specified	Feb. 28, 2014	Sep. 30, 2014	Sep. 30, 2013
		Segment
Regulatory Assets [Abstract]	'	'	'
Number of operating segment	'	1	'
Number of common stock issued through public offering	3,450,000	'	'
Net proceeds after underwriting discounts, commissions and offering expenses	'	$40,099	$64,887

Summary_of_Significant_Account2

Summary of Significant Accounting Policies - Summary of Assets Recorded at Fair Value (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Money market funds [Member]	'	'
Assets	'	'
Assets	$8,925	$6,456
Money market funds [Member] | Level 1 [Member]	'	'
Assets	'	'
Assets	8,925	6,456
U.S. Treasury securities [Member]	'	'
Assets	'	'
Assets	106,330	18,852
U.S. Treasury securities [Member] | Level 1 [Member]	'	'
Assets	'	'
Assets	106,330	18,852
U.S. government agency securities [Member]	'	'
Assets	'	'
Assets	10,524	48,709
U.S. government agency securities [Member] | Level 2 [Member]	'	'
Assets	'	'
Assets	10,524	48,709
Total cash equivalents and marketable securities [Member]	'	'
Assets	'	'
Assets	125,779	74,017
Total cash equivalents and marketable securities [Member] | Level 1 [Member]	'	'
Assets	'	'
Assets	115,255	25,308
Total cash equivalents and marketable securities [Member] | Level 2 [Member]	'	'
Assets	'	'
Assets	$10,524	$48,709

Summary_of_Significant_Account3

Summary of Significant Accounting Policies - Securities Excluded from Calculation of Diluted Net Loss per Share (Detail)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'	'
Securities excluded from calculation of diluted net loss per share	2,404	11,486	2,253	11,991
Options to purchase common stock [Member]	'	'	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'	'
Securities excluded from calculation of diluted net loss per share	2,404	2,235	2,253	2,235
Warrants to purchase convertible preferred stock [Member]	'	'	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'	'
Securities excluded from calculation of diluted net loss per share	'	75	'	79
Warrants to purchase common stock [Member]	'	'	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'	'
Securities excluded from calculation of diluted net loss per share	'	2	'	2
Convertible preferred stock [Member]	'	'	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'	'
Securities excluded from calculation of diluted net loss per share	'	9,174	'	9,675

Cash_Equivalents_and_Marketabl2

Cash Equivalents and Marketable Securities - Summary of Cash Equivalents and Marketable Securities (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]	'	'
AMORTIZED COST BASIS	$116,794	$67,557
UNREALIZED GAINS	61	7
UNREALIZED LOSSES	-1	-3
ESTIMATED FAIR VALUE	116,854	67,561
Money market funds [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
AMORTIZED COST BASIS	8,925	6,456
ESTIMATED FAIR VALUE	8,925	6,456
U.S. Treasury securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
AMORTIZED COST BASIS	106,274	18,848
UNREALIZED GAINS	57	4
UNREALIZED LOSSES	-1	'
ESTIMATED FAIR VALUE	106,330	18,852
U.S. government agency securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
AMORTIZED COST BASIS	10,520	48,709
UNREALIZED GAINS	4	3
UNREALIZED LOSSES	'	-3
ESTIMATED FAIR VALUE	10,524	48,709
Marketable securities including cash equivalents [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
AMORTIZED COST BASIS	125,719	74,013
UNREALIZED GAINS	61	7
UNREALIZED LOSSES	-1	-3
ESTIMATED FAIR VALUE	125,779	74,017
Cash equivalents [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
AMORTIZED COST BASIS	-8,925	-6,456
ESTIMATED FAIR VALUE	($8,925)	($6,456)

Cash_Equivalents_and_Marketabl3

Cash Equivalents and Marketable Securities - Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale Securities by Contractual Maturity (Detail) (USD $)	Sep. 30, 2014
In Thousands, unless otherwise specified
Amortized Cost And Fair Value Debt Securities [Abstract]	'
Amortized Cost, In one year or less	$96,527
Amortized Cost, In one to two years	29,192
Total marketable securities, Amortized Cost	125,719
Estimated Fair Value, In one year or less	96,574
Estimated Fair Value, In one to two years	29,205
Total marketable securities, Estimated Fair Value	$125,779

Cash_Equivalents_and_Marketabl4

Cash Equivalents and Marketable Securities - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2014
Schedule of Available-for-sale Securities [Line Items]	'
Gross unrealized losses on marketable securities	$1,000
Marketable securities [Member]	'
Schedule of Available-for-sale Securities [Line Items]	'
Sales of available-for-sale securities	$0

Equity_Incentive_Plans_Schedul

Equity Incentive Plans - Schedule of Option Activity under Stock Plans and Related Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'
NUMBER OF SHARES, Beginning balance	2,236,997
NUMBER OF SHARES, Options granted	780,195
NUMBER OF SHARES, Options exercised	-188,439
NUMBER OF SHARES, Options forfeited	-59,623
NUMBER OF SHARES, Ending balance	2,769,130
NUMBER OF SHARES, Options exercisable	1,440,891
WEIGHTED AVERAGE EXERCISE PRICE PER SHARE, Options beginning balance	$6.09
WEIGHTED AVERAGE EXERCISE PRICE PER SHARE, Options granted	$11.62
WEIGHTED AVERAGE EXERCISE PRICE PER SHARE, Options exercised	$5.29
WEIGHTED AVERAGE EXERCISE PRICE PER SHARE, Options forfeited	$7.63
WEIGHTED AVERAGE EXERCISE PRICE PER SHARE, Options ending balance	$7.67
WEIGHTED AVERAGE EXERCISE PRICE PER SHARE, Options exercisable	$6.03
WEIGHTED AVERAGE REMAINING CONTRACTUAL TERM, Options excercisable	'6 years

Equity_Incentive_Plans_Additio

Equity Incentive Plans - Additional Information (Detail) (USD $)	9 Months Ended
In Millions, except Share data, unless otherwise specified	Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Total unrecognized compensation expense related to nonvested employee and director stock options	$8.40
Unrecognized compensation expense expected to recognize, weighted-average period	'3 years 1 month 6 days
2013 Omnibus Incentive Plan [Member]	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Common stock available for future issuance	3,393,083

Equity_Incentive_Plans_Schedul1

Equity Incentive Plans - Schedule of Stock-Based Compensation Expenses Recognized (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]	'	'	'	'
Stock-based compensation expense recognized	$854	$519	$2,230	$1,554
Research and development [Member]	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]	'	'	'	'
Stock-based compensation expense recognized	383	261	1,112	661
General and administrative [Member]	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]	'	'	'	'
Stock-based compensation expense recognized	$471	$258	$1,118	$893

Equity_Incentive_Plans_Schedul2

Equity Incentive Plans - Schedule of Stock Option Assumptions (Detail) (Options [Member])	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'
Expected volatility	85.00%	85.00%	85.00%	85.00%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Minimum [Member]	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'
Expected term (years)	'5 years 4 months 24 days	'5 years 3 months 18 days	'5 years 3 months 18 days	'5 years
Risk-free interest rate	1.70%	1.40%	1.60%	0.80%
Maximum [Member]	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'
Expected term (years)	'6 years 8 months 12 days	'6 years 1 month 6 days	'6 years 8 months 12 days	'6 years 1 month 6 days
Risk-free interest rate	2.00%	1.60%	2.00%	1.60%

Collaborative_Research_and_Dev1

Collaborative Research and Development Agreements - Additional Information (Detail) (USD $)	1 Months Ended	9 Months Ended	0 Months Ended	1 Months Ended	3 Months Ended	9 Months Ended		1 Months Ended	9 Months Ended	1 Months Ended
	Feb. 28, 2014	Sep. 30, 2014	Mar. 14, 2014	Apr. 30, 2014	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014	Apr. 30, 2014	Sep. 30, 2014	Apr. 30, 2014
			Bristol-Myers Squibb Company [Member]	Bristol-Myers Squibb Company [Member]	Bristol-Myers Squibb Company [Member]	Bristol-Myers Squibb Company [Member]	Bristol-Myers Squibb Company [Member]	GSK [Member]	GSK [Member]	GSK [Member]
							Immuno-oncology collaboration [Member]			16 Equal quarterly payments [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'	'	'	'	'	'	'	'	'	'
Upfront payment	'	'	'	$20,000,000	'	'	'	'	'	'
Additional research funding received	'	'	9,500,000	'	'	'	2,300,000	2,000,000	'	1,000,000
Research agreement term	'	'	'3 years	'	'	'	'	'	'	'
Research agreement additional term	'	'	'2 years	'	'	'	'	'	'	'
Research agreement additional term description	'	'	'BMS may extend the research term for two additional one-year periods on a year-by-year basis, during which extensions we would be obligated to perform additional services as agreed to with BMS and BMS would be obligated to pay us research funding with respect to such services	'	'	'	'	'	'	'
Deferred revenue recognition research period	'	'	'	'	'	'5 years	'	'	'	'
Number of common stock issued through public offering	3,450,000	'	'	'	'	'	994,352	'	'	'
Price per share	'	'	'	'	'	'	$21.16	'	'	'
Aggregate purchase price	'	18,629,000	'	'	'	'	21,000,000	'	'	'
Deferred revenue recognized under collaboration arrangement	'	'	'	'	2,400,000	2,400,000	20,600,000	'	'	'
Recognized revenue under collaboration arrangement	'	'	'	'	2,000,000	4,100,000	'	'	'	'
Research funding payment received	'	'	'	'	'	'	'	'	$500,000	'