Five Prime Therapeutics (FPRX) 10-K 26 Mar 14 2013 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2013	Mar. 19, 2014
Document And Entity Information [Abstract]	'	'
Document Type	'10-K	'
Amendment Flag	'false	'
Document Period End Date	31-Dec-13	'
Document Fiscal Year Focus	'2013	'
Document Fiscal Period Focus	'FY	'
Trading Symbol	'FPRX	'
Entity Registrant Name	'FIVE PRIME THERAPEUTICS INC	'
Entity Central Index Key	'0001175505	'
Current Fiscal Year End Date	'--12-31	'
Entity Well-known Seasoned Issuer	'No	'
Entity Current Reporting Status	'Yes	'
Entity Voluntary Filers	'No	'
Entity Filer Category	'Non-accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	21,357,363
Entity Public Float	'	$0

Balance_Sheets

Balance Sheets (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Current assets:	'	'
Cash and cash equivalents	$8,161	$11,391
Marketable securities	67,561	26,624
Receivable from collaborative partners	296	397
Prepaid and other current assets	1,640	689
Total current assets	77,658	39,101
Property and equipment, net	3,744	4,631
Other long-term assets	389	359
Total assets	81,791	44,091
Liabilities, convertible preferred stock, and stockholders' equity (deficit)	'	'
Accounts payable	348	557
Accrued personnel-related expenses	2,957	2,250
Other accrued liabilities	2,056	2,216
Preferred stock warrant liability	'	563
Deferred revenue, current portion	7,913	7,498
Deferred rent, current portion	549	'
Total current liabilities	13,823	13,084
Deferred revenue, long-term portion	7,123	7,258
Deferred rent, long-term portion	2,146	2,448
Other long-term liabilities	673	897
Commitments	'	'
Common stock	17	1
Preferred stock	'	'
Additional paid-in capital	209,580	6,816
Accumulated other comprehensive income	3	7
Accumulated deficit	-151,574	-122,702
Total stockholders' equity (deficit)	58,026	-115,878
Total liabilities, convertible preferred stock, and stockholders' equity (deficit)	81,791	44,091
Series A convertible preferred stock [Member]	'	'
Liabilities, convertible preferred stock, and stockholders' equity (deficit)	'	'
Preferred stock	'	84,600
Series A-1 convertible preferred stock [Member]	'	'
Liabilities, convertible preferred stock, and stockholders' equity (deficit)	'	'
Preferred stock	'	11,000
Series A-2 convertible preferred stock [Member]	'	'
Liabilities, convertible preferred stock, and stockholders' equity (deficit)	'	'
Preferred stock	'	33,863
Series A-3 convertible preferred stock [Member]	'	'
Liabilities, convertible preferred stock, and stockholders' equity (deficit)	'	'
Preferred stock	'	$6,819

Balance_Sheets_Parenthetical

Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, except Share data, unless otherwise specified
Common stock, par value	$0.00	$0.00
Common stock, shares authorized	100,000,000	193,000,000
Common stock, shares issued	16,842,134	1,225,989
Common stock, shares outstanding	16,842,134	1,225,989
Preferred stock, par value	$0.00	$0.00
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Series A convertible preferred stock [Member]	'	'
Preferred stock, par value	$0.00	$0.00
Preferred stock, shares authorized	0	85,676,349
Preferred stock, shares issued	0	6,878,001
Preferred stock, shares outstanding	0	6,878,001
Preferred stock, aggregate liquidation preference	$0	$84,600
Series A-1 convertible preferred stock [Member]	'	'
Preferred stock, par value	$0.00	$0.00
Preferred stock, shares authorized	0	7,006,369
Preferred stock, shares issued	0	569,623
Preferred stock, shares outstanding	0	569,623
Preferred stock, aggregate liquidation preference	0	11,000
Series A-2 convertible preferred stock [Member]	'	'
Preferred stock, par value	$0.00	$0.00
Preferred stock, shares authorized	0	25,828,254
Preferred stock, shares issued	0	2,099,842
Preferred stock, shares outstanding	0	2,099,842
Preferred stock, aggregate liquidation preference	0	47,782
Series A-3 convertible preferred stock [Member]	'	'
Preferred stock, par value	$0.00	$0.00
Preferred stock, shares authorized	0	4,694,836
Preferred stock, shares issued	0	381,693
Preferred stock, shares outstanding	0	381,693
Preferred stock, aggregate liquidation preference	$0	$10,000

Statements_of_Operations

Statements of Operations (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Statement [Abstract]	'	'	'
Collaboration revenue, including revenues from related party of $7,150 for 2011	$13,791	$9,983	$64,916
Operating expenses:	'	'	'
Research and development	32,785	28,778	34,039
General and administrative	10,427	9,009	11,216
Total operating expenses	43,212	37,787	45,255
(Loss) income from operations	-29,421	-27,804	19,661
Interest income	62	88	114
Other income (expense), net	487	121	-65
Net (loss) income	-28,872	-27,595	19,710
Net income attributable to participating securities	'	'	18,823
Net (loss) income attributable to common stockholders	($28,872)	($27,595)	$887
Net (loss) income per share attributable to common stockholders	'	'	'
Basic	($5.23)	($23.05)	$0.77
Diluted	($5.23)	($23.05)	$0.72
Weighted-average shares used to compute net (loss) income per share attributable to common stockholders:	'	'	'
Basic	5,523	1,197	1,152
Diluted	5,523	1,197	1,904

Statements_of_Operations_Paren

Statements of Operations (Parenthetical) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2011
Income Statement [Abstract]	'
Revenues from related party	$7,150

Statements_of_Comprehensive_Lo

Statements of Comprehensive (Loss) Income (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement Of Income And Comprehensive Income [Abstract]	'	'	'
Net (loss) income	($28,872)	($27,595)	$19,710
Other comprehensive income (loss):	'	'	'
Net unrealized (loss) gain on marketable securities	-4	-3	10
Comprehensive (loss) income	($28,876)	($27,598)	$19,720

Statement_of_Convertible_Prefe

Statement of Convertible Preferred Stock and Stockholders' Deficit (USD $)

Total

Initial Public Offering [Member]

Underwriters [Member]

Convertible preferred stock [Member]

Convertible preferred stock [Member]

Common Stock [Member]

Common Stock [Member]

Common Stock [Member]

Additional Paid-in Capital [Member]

Additional Paid-in Capital [Member]

Additional Paid-in Capital [Member]

Accumulated Other Comprehensive Income [Member]

Accumulated Deficit [Member]

In Thousands, except Share data

Series A3 Convertible Preferred Stock [Member]

Initial Public Offering [Member]

Underwriters [Member]

Initial Public Offering [Member]

Underwriters [Member]

Beginning Balance at Dec. 31, 2010

($112,792)

'

'

$129,463

'

$1

'

'

$2,024

'

'

'

($114,817)

Beginning Balance, Shares at Dec. 31, 2010

'

'

'

9,547,466

'

1,135,629

'

'

'

'

'

'

'

Stock option exercises, net

39

'

'

'

'

'

'

'

39

'

'

'

'

Stock option exercises, Shares

26,152

'

'

'

'

26,152

'

'

'

'

'

'

'

Stock-based compensation expense related to employee and director option grants

2,850

'

'

'

'

'

'

'

2,850

'

'

'

'

Nonemployee stock-based compensation expense

77

'

'

'

'

'

'

'

77

'

'

'

'

Other comprehensive income

10

'

'

'

'

'

'

'

'

'

'

10

'

Net income (loss)

19,710

'

'

'

'

'

'

'

'

'

'

'

19,710

Ending Balance at Dec. 31, 2011

-90,106

'

'

129,463

'

1

'

'

4,990

'

'

10

-95,107

Ending Balance, Shares at Dec. 31, 2011

'

'

'

9,547,466

'

1,161,781

'

'

'

'

'

'

'

Issuance of stock, net of issuance costs

'

'

'

'

6,819

'

'

'

'

'

'

'

'

Issuance of stock, Shares

'

'

'

'

381,693

'

'

'

'

'

'

'

'

Stock option exercises, net

105

'

'

'

'

'

'

'

105

'

'

'

'

Stock option exercises, Shares

64,208

'

'

'

'

64,208

'

'

'

'

'

'

'

Stock-based compensation expense related to employee and director option grants

1,655

'

'

'

'

'

'

'

1,655

'

'

'

'

Nonemployee stock-based compensation expense

66

'

'

'

'

'

'

'

66

'

'

'

'

Other comprehensive income

-3

'

'

'

'

'

'

'

'

'

'

-3

'

Net income (loss)

-27,595

'

'

'

'

'

'

'

'

'

'

'

-27,595

Ending Balance at Dec. 31, 2012

-115,878

'

'

136,282

'

1

'

'

6,816

'

'

7

-122,702

Ending Balance, Shares at Dec. 31, 2012

'

'

'

9,929,159

'

1,225,989

'

'

'

'

'

'

'

Conversion of preferred stock to common stock

136,282

'

'

-136,282

'

10

'

'

136,272

'

'

'

'

Conversion of preferred stock to common stock, Shares

'

'

'

-9,929,159

'

9,929,159

'

'

'

'

'

'

'

Issuance of stock, net of issuance costs

'

55,144

8,705

'

'

'

5

1

'

55,139

8,704

'

'

Issuance of stock, Shares

'

'

'

'

'

'

4,800,000

720,000

'

'

'

'

'

Stock option exercises, net

440

'

'

'

'

'

'

'

440

'

'

'

'

Stock option exercises, Shares

168,359

'

'

'

'

162,610

'

'

'

'

'

'

'

Reclassification of warrant liability to additional paid-in capital upon conversion of warrant to purchase Series A convertible preferred stock to warrant to purchase common stock

6

'

'

'

'

'

'

'

6

'

'

'

'

Issuance of common stock upon automatic net exercise of warrant

57

'

'

'

'

'

'

'

57

'

'

'

'

Issuance of common stock upon automatic net exercise of warrants, Shares

'

'

'

'

'

4,376

'

'

'

'

'

'

'

Stock-based compensation expense related to employee and director option grants

2,067

'

'

'

'

'

'

'

2,067

'

'

'

'

Nonemployee stock-based compensation expense

79

'

'

'

'

'

'

'

79

'

'

'

'

Other comprehensive income

-4

'

'

'

'

'

'

'

'

'

'

-4

'

Net income (loss)

-28,872

'

'

'

'

'

'

'

'

'

'

'

-28,872

Ending Balance at Dec. 31, 2013

$58,026

'

'

'

'

$17

'

'

$209,580

'

'

$3

($151,574)

Ending Balance, Shares at Dec. 31, 2013

'

'

'

'

'

16,842,134

'

'

'

'

'

'

'

Statement_of_Convertible_Prefe1

Statement of Convertible Preferred Stock and Stockholders' Deficit (Parenthetical) (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2012
Statement Of Stockholders Equity [Abstract]	'
Convertible preferred stock issued, price per share	$26.20
Convertible preferred stock issued, issuance costs	$35
Convertible preferred stock issued, fair value adjustment	$3,146

Statements_of_Cash_Flows

Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating activities	'	'	'
Net (loss) income	($28,872)	($27,595)	$19,710
Adjustments to reconcile net (loss) income to net cash provided by (used in) operating activities:	'	'	'
Depreciation and amortization	1,694	1,643	1,631
(Gain) loss on disposal of property and equipment	'	-5	2
Stock-based compensation expense	2,146	1,721	2,927
Amortization of premium on marketable securities	432	538	892
Revaluation of preferred stock warrant liability	-500	-119	60
Changes in operating assets and liabilities:	'	'	'
Receivable from collaborative partners	101	449	-846
Prepaid, other current assets, and other long-term assets	-981	372	-313
Accounts payable	-209	196	-729
Accrued personnel-related expenses	707	-19	656
Payable to collaborative partner	'	-3,000	3,000
Deferred revenue	280	7,379	-5,188
Deferred rent	247	457	696
Other accrued liabilities and other long-term liabilities	-375	-414	789
Net cash provided by (used in) operating activities	-25,330	-18,397	23,287
Investing activities	'	'	'
Purchases of marketable securities	-79,776	-45,419	-71,773
Maturities of marketable securities	38,403	64,636	45,738
Purchases of property and equipment	-807	-737	-970
Change in restricted cash	'	38	'
Net cash provided by (used in) investing activities	-42,180	18,518	-27,005
Financing activities	'	'	'
Proceeds from issuances of common stock	63,849	'	'
Proceeds from issuances of convertible preferred stock (net of issuance costs)	'	6,819	'
Proceeds from issuances of exercise of stock options	440	105	39
Payments under capital lease obligation	-9	-15	-13
Net cash provided by financing activities	64,280	6,909	26
Net increase (decrease) in cash and cash equivalents	-3,230	7,030	-3,692
Cash and cash equivalents at beginning of year	11,391	4,361	8,053
Cash and cash equivalents at end of year	$8,161	$11,391	$4,361

Organization_and_Summary_of_Si

Organization and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
Organization and Summary of Significant Accounting Policies	'
	1. Organization and Summary of Significant Accounting Policies
	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.
	Initial Public Offering
	In September 2013, we completed our initial public offering of shares of our common stock, or IPO, pursuant to which we issued 5,520,000 shares of common stock, which includes shares we issued pursuant to our underwriters’ exercise of their over-allotment option, and received net proceeds of $63.8 million, after underwriting discounts, commissions and offering expenses. In addition, in connection with the completion of our IPO, all convertible preferred stock converted into common stock.
	Use of Estimates
	The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ materially from those estimates.
	Reverse Stock Split
	On September 4, 2013, the Company effected a 1-for-12.3 reverse stock split. All information in this report relating to the number of shares, price per share and per share amounts of stock gives retroactive effect to the 1-for-12.3 reverse stock split of the Company’s stock.
	Reclassifications
	Certain prior period amounts have been reclassified 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 the balance sheets, and made related conforming reclassifications on the statement of cash flows.
	Cash and Cash Equivalents
	We consider all highly liquid investments purchased with original maturities of three months or less at the date of purchase to be cash equivalents. Cash equivalents are stated at fair value.
	Marketable Securities
	All marketable securities have been classified as “available for sale” and are carried at fair value, based upon quoted market prices. We consider our available-for-sale portfolio as available for use in current operations. Accordingly, we may classify certain investments as short-term marketable securities, even though the stated maturity date may be one year or more beyond the current balance sheet date. Unrealized gains and losses, net of any related tax effects, are excluded from earnings and are included in other comprehensive income and reported as a separate component of stockholders’ deficit until realized. Realized gains and losses and declines in value judged to be other than temporary, if any, on available-for-sale securities are included in other income (expense), net. The cost of securities sold is based on the specific-identification method. The amortized cost of securities is adjusted for amortization of premiums and accretion of discounts to maturity. Interest on short-term investments is included in interest income. In accordance with our investment policy, management invests to diversify credit risk and only invests in debt securities with high credit quality, including U.S. government securities, and does not invest in mortgage-backed securities or mortgage loans.
	We periodically evaluate whether declines in the fair value of our investments below their cost are other than temporary. The evaluation includes consideration of the cause of the impairment, including the creditworthiness of the security issuers, the number of securities in an unrealized loss position, the severity and duration of the unrealized losses, whether we have the intent to sell the securities, and whether it is more likely than not that we will be required to sell the securities before the recovery of their amortized cost basis. If we determine that the decline in fair value of an investment is below its accounting basis and this decline is other than temporary, we would reduce the carrying value of the security we hold and record a loss for the amount of such decline. We have not recorded any realized losses or declines in value judged to be other than temporary on our investments in debt securities.
	Restricted Cash
	We had a certificate of deposit that served as collateral under a revolving credit agreement. Amounts related to the certificate of deposit were reported as short-term restricted cash and totaled $38,000 at December 31, 2011. In March 2012, we terminated this revolving credit agreement, and the certificate of deposit was refunded to us in 2012.
	Concentrations of Credit Risk
	Financial instruments that potentially subject us to significant concentrations of credit risk consist primarily of cash and cash equivalents and marketable securities. Cash and cash equivalents and marketable securities are invested through banks and other financial institutions in the United States. Such deposits in the United States may be in excess of insured limits.
	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. For our marketable securities, we review trading activity and pricing as of the measurement date. When sufficient quoted pricing for identical securities is not available, we use market pricing and other observable market inputs for similar securities obtained from various third-party data providers. These inputs either represent quoted prices for similar assets in active markets or have been derived from observable market data; 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.
	Level 1 securities consist of highly liquid money market funds and U.S. Treasury securities. The fair value of Level 1 assets has been determined using quoted prices in active markets for identical assets. Level 2 securities consist of U.S. government agency securities and were measured at fair value using Level 2 inputs. We review trading activity and pricing for these 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, were derived from observable market data, or, if not directly observable, were derived from or corroborated by other observable market data. There were no transfers between Level 1 and Level 2 securities in the periods presented.
	In certain cases where there is limited activity or less transparency around inputs to valuation, securities are classified as Level 3 within the valuation hierarchy. As of December 31, 2012, our Level 3 liability consisted of a preferred stock warrant liability that we measured at estimated fair value. Prior to our IPO in September 2013, we had outstanding warrants which were classified as a liability and remeasured to fair value each reporting period. We measured the estimated fair value of the preferred stock warrant liability using the Black-Scholes option-pricing model. Inputs used to determine estimated fair value include the estimated fair value of the underlying stock at the valuation measurement date, the remaining contractual term of the warrants, risk-free interest rates, expected dividends, and the expected volatility of the price of the underlying stock. In connection with the completion of the Company’s IPO in September 2013, substantially all of the warrants were automatically net exercised for a total of 4,376 shares, pursuant to the terms of the warrants. As a result of the net exercises, we recorded an $83,000 gain related to the change in fair value as part of other income, net on our statement of operations and reclassified the fair value of $57,000 to permanent equity. These warrants were remeasured using the intrinsic value of the warrant and the net settlement value based on the $13.00 per share IPO price. The remaining outstanding warrant to purchase Series A convertible preferred stock converted into a warrant to purchase 2,304 shares of common stock at $12.30 per share. We remeasured the fair value of these remaining warrants through the date of the conversion to a common stock warrant and we recorded a $3,000 loss related to the change in fair value as part of other income, net on our statement of operations and reclassified the fair value of $6,000 to permanent equity. The common stock warrant was automatically net exercised for a total of 768 shares on January 26, 2014. The Level 3 liability that is measured at estimated fair value on a recurring basis consists of the preferred stock warrant liability. The estimated fair value of the outstanding preferred stock warrant liability is measured using the Black-Scholes option-pricing model. Inputs used to determine estimated fair value include the estimated fair value of the underlying stock at the valuation measurement date, the remaining contractual term of the warrants, risk-free interest rates, expected dividends, and the expected volatility of the price of the underlying stock.
	The following table summarizes, for assets and the liability recorded at fair value, the respective fair value and the classification by level of input within the fair value hierarchy defined above (in thousands):
			DECEMBER 31, 2013
						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		$	—
			DECEMBER 31, 2012
						BASIS OF FAIR VALUE MEASUREMENTS
			TOTAL			LEVEL 1			LEVEL 2			LEVEL 3
	Assets
	Money market funds		$	6,910		$	6,910		$	—		$	—
	U.S. Treasury securities			3,577			3,577			—			—
	U.S. government agency securities			23,047			—			23,047			—
	Total cash equivalents and marketable securities		$	33,534		$	10,487		$	23,047		$	—
	Liability
	Preferred stock warrant liability		$	563		$	—		$	—		$	563
	The change in the estimated fair value of the preferred stock warrant liability is summarized below (in thousands):
			YEARS ENDED DECEMBER 31
			2013			2012			2011
	Balance, beginning of year		$	563		$	682		$	622
	Change in fair value recorded in other income (expense), net			(500	)		(119	)		60
	Exercises			(57	)		—			—
	Conversion of preferred stock warrant to common stock warrant and reclassification to permanent equity			(6	)		—			—
	Balance, end of year		$	—		$	563		$	682
	The fair value of the above warrants was determined using the Black-Scholes valuation model with the following assumptions:
			DECEMBER 31
			2012			2011
	Risk-free interest rate			0.2%—0.3%			0.1%—0.4%
	Remaining contractual term (years)			2.1			3
	Volatility			85.00%			85.00%
	Property and Equipment
	Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful lives of the assets, ranging from three to five years. Leasehold improvements are amortized over the shorter of their estimated useful lives or the related lease term.
	Impairment of Long-Lived Assets
	Long-lived assets include property and equipment. The carrying value of long-lived assets is reviewed for impairment whenever events or changes in circumstances indicate that the assets may not be recoverable. An impairment loss is recognized when the total estimated future cash flows expected to result from the use of the asset and its eventual disposition are less than the carrying amount. Through December 31, 2013, there have been no such impairment losses.
Preferred Stock Warrant Liability
Freestanding warrants for shares that are either putable or redeemable are classified as liabilities on the balance sheet at fair value. Therefore, the freestanding warrants that give the holders the right to purchase our convertible preferred stock are liabilities that are recorded at estimated fair value. At the end of each reporting period, changes in fair value during the period are recorded as a component of other income (expense), net.
We adjusted the liability for changes in the estimated fair value of the warrants until the earlier of the exercise or expiration of the warrants to purchase shares of convertible preferred stock or the completion of a liquidation event, including the completion of an initial public offering, at which time the liabilities were reclassified to stockholders’ deficit.
Revenue Recognition
We recognize revenue when all of the following criteria are met: persuasive evidence of an arrangement exists; transfer of technology has been completed or services have been rendered; our price to the customer is fixed or determinable and collectability is reasonably assured.
The terms of our collaborative research and development agreements include nonrefundable upfront and license fees, research funding, milestone and other contingent payments to us for the achievement of defined collaboration objectives and certain preclinical, clinical, regulatory and sales-based events, as well as royalties on sales of any commercialized products.
Multiple-Element Revenue Arrangements. Our collaborations primarily represent multiple-element revenue arrangements. To account for these transactions, we determine the elements, or deliverables, included in the arrangement and determine which deliverables are separable for accounting purposes. We consider delivered items to be separable if the delivered items have stand-alone value to the customer. If the delivered items are separable, we allocate arrangement consideration to the various elements based on each element’s relative selling price. The identification of individual elements in a multiple-element arrangement and the estimation of the selling price of each element involve significant judgment, including consideration as to whether each delivered element has standalone value to the customer. We determine the estimated selling price for deliverables within each agreement using vendor-specific objective evidence (VSOE) of selling price, if available, or third party evidence of selling price if VSOE is not available, or our best estimate of selling price, if neither VSOE nor third party evidence is available. Determining the best estimate of selling price for a deliverable requires significant judgment. We use our best estimate of selling price to estimate the selling price for licenses to our proprietary technology, since we do not have VSOE or third party evidence of selling price for these deliverables.
We recognize consideration allocated to an individual element when all other revenue recognition criteria are met for that element. Our multiple-element revenue arrangements generally include the following:
	•		Exclusive Licenses. The deliverables under our collaboration agreements generally include exclusive licenses to discover, develop, manufacture and commercialize compounds with respect to one or more specified targets. To account for this element of the arrangement, we evaluate whether the exclusive license has standalone value apart from the undelivered elements to the collaboration partner based on the consideration of the relevant facts and circumstances of each arrangement, including the research and development capabilities of the collaboration partner and other market participants. We recognize arrangement consideration allocated to licenses upon delivery of the license, if facts and circumstances indicate that the license has standalone value apart from the undelivered elements, which generally include research and development services. If facts and circumstances indicate that the delivered license does not have standalone value from the undelivered elements, we recognize the revenue as a combined unit of accounting.
We have determined that some of our exclusive licenses lack standalone value apart from the related research and development services. In those circumstances we recognize collaboration revenue from non-refundable exclusive license fees in the same manner as the undelivered item(s), which is generally the period over which we provide the research and development services.
	•		Research and Development Services. The deliverables under our collaboration and license agreements generally include deliverables related to research and development services we perform on behalf of the collaboration partner. As the provision of research and development services is a part of our central operations and we are principally responsible for the performance of these services under the agreements, we recognize revenue on a gross basis for research and development services as we perform those services. Additionally, we recognize research funding related to collaborative research and development efforts as revenue as we perform or deliver the related services in accordance with contract terms as long as we will receive payment for such services upon standard payment terms.
Milestone Revenue. Our collaboration and license agreements generally include contingent payments and milestone payments related to specified research, development and regulatory milestones and sales-based milestones. Research, development and regulatory contingent payments and milestone payments are typically payable under our collaborations when our collaborator claims or selects a target, or initiates or advances a covered product candidate in preclinical or clinical development, upon submission for marketing approval of a covered product with regulatory authorities, upon receipt of actual marketing approvals of a covered product or for additional indications, or upon the first commercial sale of a covered product. Sales-based milestones are typically payable when annual sales of a covered product reach specified levels.
At the inception of each arrangement that includes milestone payments, we evaluate whether each milestone is substantive and at risk to both parties on the basis of the contingent nature of the milestone. We evaluate factors such as the scientific, regulatory, commercial and other risks that we must overcome to achieve the respective milestone, the level of effort and investment required to achieve the respective milestone and whether the milestone consideration is reasonable relative to all deliverables and payment terms in the arrangement in making this assessment.
We have elected to adopt the Financial Accounting Standards Board Accounting Standards Update 2010-17, Revenue Recognition—Milestone Method, such that we recognize any payment that is contingent upon the achievement of a substantive milestone entirely in the period in which the milestone is achieved. A milestone is defined as an event that can only be achieved based in whole or in part on either our performance or the occurrence of a specific outcome resulting from our performance for which there is substantive uncertainty at the date the arrangement is entered into that the event will be achieved. Therefore, a milestone does not include events for which occurrence is contingent solely on the performance of a collaborative partner. To be substantive, a milestone must meet all the following criteria: the consideration receivable upon the achievement of the milestone is commensurate with either our performance to achieve the milestone or the enhancement of value of delivered items as a result of a specific outcome resulting from our performance to achieve the milestone, the consideration relates solely to past performance, and the consideration is reasonable relative to all of the deliverables and payment terms in the arrangement.
Research and Development Expenses
Research and development expenses consist of costs we incur for our own and for sponsored and collaborative research and development activities. Expenses we incur related to collaborative research and development agreements approximate the revenue recognized under these agreements. Research and development costs are expensed as incurred. Research and development costs consist of salaries and benefits, including associated stock-based compensation, laboratory supplies and facility costs, as well as fees paid to other entities that conduct certain research and development activities on our behalf. We estimate preclinical study and clinical trial expenses based on the services performed pursuant to contracts with research institutions and clinical research organizations that conduct and manage preclinical studies and clinical trials on our behalf based on actual time and expenses incurred by them. Further, we accrue expenses related to clinical trials based on the level of patient enrollment and activity according to the related agreement. We monitor patient enrollment levels and related activity to the extent reasonably possible and adjust estimates accordingly.
We expense payments for the acquisition and development of technology as research and development costs if, at the time of payment: the technology is under development; is not approved by the U.S. Food and Drug Administration or other regulatory agencies for marketing; has not reached technical feasibility; or otherwise has no foreseeable alternative future use.
Stock-Based Compensation
We recognize compensation expense using a fair-value-based method for costs related to all share-based payments, including stock options. Stock-based compensation cost related to employees and directors is measured at the grant date, based on the fair-value-based measurement of the award estimated using the Black-Scholes option-pricing model, and is recognized as expense over the requisite service period on a straight-line basis. We are required to estimate forfeitures at the time of grant and revise those estimates in subsequent periods if actual forfeitures differ from those estimates. We use historical data to estimate prevesting option forfeitures and record stock-based compensation expense only for those awards that are expected to vest. We recorded stock-based compensation expense for stock-based awards to employees and directors of approximately $2,067,000, $1,655,000 and $2,850,000 for the years ended December 31, 2013, 2012 and 2011, respectively.
Options granted to individual service providers who are not employees or directors are accounted for at estimated fair value using the Black-Scholes option-pricing model and are subject to periodic remeasurement over the period during which the services are rendered. Stock-based compensation expense related to options granted to individual service providers who are not employees or directors was approximately $79,000, $66,000 and $77,000 for the years ended December 31, 2013, 2012 and 2011, respectively.
Income Taxes
We account for income taxes using the liability method, under which deferred tax assets and liabilities are determined based on differences between financial reporting and tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. Valuation allowances are provided when the expected realization of the deferred tax assets does not meet the more-likely-than-not criteria. We are required to determine whether it is more likely than not that a tax position will be sustained upon examination by the appropriate taxing authorities before any part of the benefit can be recorded in the financial statements. It is our practice to recognize interest and penalties related to unrecognized tax benefits, if any, as a component of income tax expense.
Net (Loss) Income Per Share
We compute net (loss) income per share of common stock using the two-class method required for participating securities. We consider all series of our convertible preferred stock to be participating securities. In accordance with the two-class method, earnings allocated to these participating securities, which include participation rights in undistributed earnings, are subtracted from net income to determine total undistributed earnings to be allocated to common stockholders.
Basic net (loss) income per common share is computed by dividing net (loss) income attributable to common stockholders by the weighted-average number of common shares outstanding during the period. All participating securities are excluded from basic weighted-average common shares outstanding. In computing diluted net (loss) income attributable to common stockholders, undistributed earnings are re-allocated to reflect the potential impact of dilutive securities, including stock options and warrants. Diluted net (loss) income per share attributable to common stockholders is computed by dividing net (loss) income attributable to common stockholders by the weighted-average number of common equivalent shares outstanding for the period. Diluted net (loss) income per share attributable to common stockholders includes any dilutive effect from outstanding stock options and warrants using the treasury stock method.
The following common stock issuable upon the conversion or exercise of dilutive securities has been excluded from the diluted net (loss) income per share attributable to common stockholders calculation because their effect would have been antidilutive for the periods presented:
(Shares in thousands)		YEARS ENDED
		DECEMBER 31,
		2013			2012			2011
Convertible preferred stock			7,209			9,824			—
Options to purchase common stock			2,338			2,347			551
Warrants to purchase convertible preferred stock			61			87			88
Warrants to purchase common stock			1			—			—
			9,609			12,258			639
		YEARS ENDED DECEMBER 31,
(in thousands, except per share data)		2013			2012			2011
Basic
Numerator:
Net (loss) income		$	(28,872	)	$	(27,595	)	$	19,710
Net income attributable to participating securities			—			—			(18,823	)
Net (loss) income attributable to common stockholders for basic net (loss) income per share		$	(28,872	)	$	(27,595	)	$	887
Denominator:
Weighted-average common shares outstanding			5,523			1,197			1,152
Basic net (loss) income per common share		$	(5.23	)	$	(23.05	)	$	0.77
Diluted
Numerator:
Net (loss) income attributable to common stockholders for basic net (loss) income per share		$	(28,872	)	$	(27,595	)	$	887
Reallocation of net income attributable to participating securities			—			—			483
Net (loss) income attributable to common stockholders for diluted net (loss) income per share		$	(28,872	)	$	(27,595	)	$	1,370
Denominator:
Weighted-average number of common shares outstanding used in computing basic net (loss) income per common share			5,523			1,197			1,152
Dilutive effect of:
Stock options			—			—			752
Weighted-average number of common shares outstanding used in computing diluted net (loss) income per common share			5,523			1,197			1,904
Diluted net (loss) income per common share		$	(5.23	)	$	(23.05	)	$	0.72

Cash_Equivalents_and_Marketabl

Cash Equivalents and Marketable Securities	12 Months Ended
	Dec. 31, 2013
Cash And Cash Equivalents [Abstract]	'
Cash Equivalents and Marketable Securities	'
	2. Cash Equivalents and Marketable Securities
	The following is a summary of our cash equivalents and marketable securities at December 31, 2013 and 2012:
	(in thousands)	DECEMBER 31, 2013
		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
	(in thousands)	DECEMBER 31, 2012
		AMORTIZED			UNREALIZED		UNREALIZED			ESTIMATED
		COST BASIS			GAINS		LOSSES			FAIR VALUE
	Money market funds	$	6,910		$	—	$	—		$	6,910
	U.S. Treasury securities		3,576			1		—			3,577
	U.S. government agency securities		23,041			6		—			23,047
			33,527			7		—			33,534
	Less: cash equivalents		(6,910	)		—		—			(6,910	)
	Total marketable securities	$	26,617		$	7	$	—		$	26,624
	As of December 31, 2013, 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
	Debt securities maturing:
	In one year or less	$	66,459		$	66,461
	In one to two years		7,554			7,556
	Total marketable securities	$	74,013		$	74,017
	We determined that the gross unrealized losses of $3,000 on our marketable securities as of December 31, 2013 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 December 31, 2013. There were no sales of available-for-sale securities in any of the periods presented.

Property_and_Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2013
Property Plant And Equipment [Abstract]	'
Property and Equipment	'
	3. Property and Equipment
	Property and equipment consist of the following:
	(in thousands)	DECEMBER 31
		2013			2012
	Computer equipment and software	$	1,097		$	1,145
	Furniture and fixtures		694			690
	Laboratory equipment		9,596			9,112
	Leasehold improvements		2,173			2,135
			13,560			13,082
	Less: accumulated depreciation and amortization		(9,816	)		(8,451	)
	Property and equipment, net	$	3,744		$	4,631

Preferred_Stock_and_Common_Sto

Preferred Stock and Common Stock Warrant	12 Months Ended
	Dec. 31, 2013
Text Block [Abstract]	'
Preferred Stock and Common Stock Warrant	'
	4. Preferred Stock and Common Stock Warrant
	In December 2002, pursuant to the terms of an equipment loan and security agreement, we issued a fully exercisable warrant to the lender for the purchase of 3,902 shares of Series A convertible preferred stock at an exercise price of $12.30 per share. The warrant was exercisable through December 2012, subject to certain conditions. The warrant expired unexercised in December 2012.
	In June 2004, pursuant to the terms of an equipment loan and security agreement, we issued a fully exercisable warrant to the lender for the purchase of 2,304 shares of Series A convertible preferred stock at an exercise price of $12.30 per share. In connection with the completion of the Company’s IPO in September 2013, the warrant converted into a warrant to purchase 2,304 shares of common stock at $12.30 per share. We remeasured the fair value of these remaining warrants through the date of the conversion to a common stock warrant and we recorded a $3,000 loss related to the change in fair value as part of other income, net on our statement of operations and reclassified the fair value of $6,000 to permanent equity. The warrant was automatically net exercised for a total of 768 shares on January 26, 2014.
	In connection with the issuance of Series A convertible preferred stock in January and February 2005, we issued a warrant to purchase 81,300 shares of Series A convertible preferred stock at $12.30 per share to our preferred stock placement agent. During 2007, the warrant was canceled and replaced by the issuance of two warrants for 44,715 and 36,585 shares; all other terms remained unchanged. In connection with the completion of the Company’s IPO in September 2013, the warrants were automatically net exercised for a total of 4,376 shares, pursuant to the terms of the warrants. As a result of the net exercises, we recorded an $83,000 gain related to the change in fair value as part of other income, net on our statement of operations and reclassified the fair value of $57,000 to permanent equity. These warrants were remeasured using the intrinsic value of the warrant and the net settlement value based on the $13.00 per share IPO price.

Commitments

Commitments	12 Months Ended
	Dec. 31, 2013
Commitments And Contingencies Disclosure [Abstract]	'
Commitments	'
	5. Commitments
	In March 2010, we entered into office and laboratory facility lease agreements for a facility located in South San Francisco, California. These leases enable us to utilize the facility through December 31, 2017, with an option to extend the term for an additional three years. The leases require us to pay rent as well as additional amounts for operating expenses and maintenance.
	The minimum annual rent under the leases is subject to increases based on stated rental adjustment terms. For financial reporting purposes, rent expense is recognized on a straight-line basis over the term of the leases. Accordingly, rent expense recognized in excess of rent paid is reflected as deferred rent. Deferred rent totaled $2.7 million and $2.4 million at December 31, 2013 and 2012, respectively. In addition, the leases contain a $1.7 million incentive in the form of reimbursement or payments from the landlord for a portion of the costs of leasehold improvements we make to the facility. We made these improvements and received the benefit of the $1.7 million incentive in 2010. The assets purchased with the incentive are included in property and equipment, net in the accompanying balance sheets as of December 31, 2013 and 2012, respectively. The incentive is being recognized as a reduction of rental expense on a straight-line basis over the term of the underlying leases. The unamortized leasehold improvement incentive totaled $0.9 million and $1.1 million as of December 31, 2013 and 2012, respectively, of which $0.7 million and $0.9 million is included in other long-term liabilities in the accompanying balance sheets as of December 31, 2013 and 2012, respectively.
	Rent expense for each of the years ended December 31, 2013, 2012 and 2011 was $1.9 million. The estimated future minimum commitments under these noncancelable operating leases are as follows:
	(in thousands)
	Year ending December 31:
	2014		2,710
	2015		2,794
	2016		2,877
	2017		2,960
	Total estimated minimum payments	$	11,341

Convertible_Preferred_Stock

Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2013
Equity [Abstract]	'
Convertible Preferred Stock	'
	6. Convertible Preferred Stock
	In connection with the completion of the Company’s IPO in September 2013, all outstanding shares of convertible preferred stock converted into 9,929,159 shares of common stock.

Stockholders_Equity_Deficit

Stockholders' Equity (Deficit)	12 Months Ended
	Dec. 31, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'
Stockholders' Equity (Deficit)	'
	7. Stockholders’ Equity (Deficit)
	Stock Option Plans
	Our Board of Directors, or Board, and stockholders previously approved the 2002 Equity Incentive Plan, or the 2002 Plan, and the 2010 Equity Incentive Plan, or the 2010 Plan, and collectively with the 2002 Plan, the Prior Plans. The 2002 Plan terminated in March 2012. In September 2013, our stockholders approved the 2013 Omnibus Incentive Plan, or the 2013 Plan. As of September 23, 2013, the effective date of the 2013 Plan, we suspended the 2010 Plan and no additional awards may be granted under the 2010 Plan. Any shares of common stock covered by awards granted under the Prior Plans that terminate after September 23, 2013 by expiration, forfeiture, cancellation or other means without the issuance of such shares, will be added to the 2013 Plan reserve.
	The initial number of shares of common stock available for issuance under the 2013 Plan was 3,500,000, which includes the 1,069,985 shares of common stock that were available for issuance under the Prior Plans as of the effective date of the 2013 Plan. Unless our Board provides otherwise, beginning on January 1, 2014 and continuing until the expiration of the 2013 Plan, the total number of shares of common stock available for issuance under the 2013 Plan will automatically increase annually on January 1 by 4% of the total number of issued and outstanding shares of common stock as of December 31 of the immediately preceding year.
	Incentive stock options may be granted with an exercise price of not less than estimated fair value, and nonstatutory stock options may be granted with an exercise price of not less than 85% of the estimated fair value of the common stock on the date of grant. Stock options granted to a stockholder owning more than 10% of our voting stock must have an exercise price of not less than 110% of the estimated fair value of the common stock on the date of grant. For all stock options granted prior to our IPO, our Board determined the estimated fair value of our common stock. For all stock options granted after the completion of our IPO in September 2013, the fair value for our underlying common stock is determined using the closing price as reported on The NASDAQ Global Market or The NASDAQ Global Select Market, as applicable, on the date of grant. Stock options are granted with terms of up to ten years and generally vest over a period of four years.
	In September 2013, our stockholders approved the 2013 Employee Stock Purchase Plan, or the ESPP, which became effective as of September 23, 2013. We have initially reserved a total of 250,000 shares of common stock for issuance under the ESPP. Unless our Board provides otherwise, beginning on January 1, 2014 and continuing until the expiration of the ESPP, the total number of shares of common stock available for issuance under the ESPP will automatically increase annually on January 1 by the lesser of (i) 1% of the total number of issued and outstanding shares of common stock as of December 31 of the immediately preceding year, or (ii) 300,000 shares of common stock.
	The following table summarizes option activity under our stock plans and related information:
		OPTIONS OUTSTANDING
		NUMBER			WEIGHTED-
		OF SHARES			AVERAGE
					EXERCISE PRICE
					PER SHARE
	Balance at December 31, 2010		1,996,513		$	4.06
	Options granted		448,443		$	8.36
	Options exercised		(26,152	)	$	1.48
	Options forfeited		(206,157	)	$	5.04
	Options expired		(21,264	)	$	3.57
	Balance at December 31, 2011		2,191,383		$	4.92
	Options granted		526,134		$	5.78
	Options exercised		(64,208	)	$	1.6
	Options forfeited		(32,611	)	$	6.89
	Options expired		(75,467	)	$	3.2
	Balance at December 31, 2012		2,545,231		$	5.17
	Options granted		584,529		$	7.08
	Options exercised		(168,359	)	$	3.07
	Options forfeited		(53,246	)	$	6.87
	Options expired		(671,158	)	$	4.12
	Balance at December 31, 2013		2,236,997		$	6.09
	Options exercisable		1,287,357		$	5.48
	As of December 31, 2013, there were 3,466,450 shares available for future issuance under the 2013 Plan.
	As of December 31, 2013, options to purchase 2,182,957 shares of common stock were outstanding that are fully vested or expected to vest with a weighted-average exercise price of $6.07 per share and a weighted-average remaining contractual term of 7.3 years. As of December 31, 2013, the weighted-average remaining contractual term for options exercisable was 6.3 years. The aggregate intrinsic value of options outstanding was $23.9 million. The aggregate intrinsic value of options exercisable was $14.6 million. The aggregate intrinsic value of options expected to vest was $23.4 million. The aggregate intrinsic value was calculated as the difference between the exercise price of the options and the closing price of common stock of $16.79 per share as of December 31, 2013.
	Restricted Stock Awards
	During 2013, we issued an award of 1,000 restricted shares of common stock under our 2013 Plan at a grant date fair value of $15.64. Restricted stock awards are share awards that entitle the holder to receive freely tradable shares of our common stock upon vesting. This restricted stock award will fully vest and become unforfeitable in March 2014. In accordance with ASC718, the fair value of the restricted stock award was based upon the closing sales price of our common stock on the grant date.
	Employee Stock Purchase Plan
	Under our ESPP, employees can purchase shares of our common stock based on a percentage of their compensation subject to certain limits. The purchase price per share is equal to the lower of 85% of the fair market value of our common stock on the offering date or the purchase date with a six-month look-back feature. ESPP purchases are settled with common stock from the ESPP’s previously authorized and available pool of shares. No shares were issued under the ESPP in 2013. A total of 250,000 shares of common stock have been reserved and available for issuance under the ESPP as of December 31, 2013.
	The compensation expense related to the ESPP during 2013 was $42,000. As of December 31, 2013, there was $0.1 million of unrecognized compensation cost related to the ESPP, which is expected to be recognized over 4.5 months.
	Stock-Based Compensation
	Effective March 2011, we amended the vesting conditions for two outstanding stock options with performance-based vesting criteria (the performance-based options). The original terms of the performance-based options provided that the options to two employees would partially vest in the event we enter into a definitive agreement for a strategic alliance or partnership with an upfront payment over $50 million. As amended, the terms of the performance-based options provide that the options would partially vest in the event we enter into one or more definitive agreements for strategic alliances or partnerships within a 12-month period with aggregate upfront payments over $50 million. As a result of the amendment, 80,649 unvested shares subject to the performance-based options vested and the modification resulted in total incremental stock-based compensation expense of $0.6 million that was recorded in 2011.
	In August 2011, we entered into a separation agreement with our former President and Chief Executive Officer (former CEO) pursuant to which (i) we accelerated the vesting of 50% of certain outstanding nonvested options held by the former CEO upon separation, which resulted in stock-based compensation of $0.5 million, and (ii) the post-termination exercise period for all of the former CEO’s outstanding vested options were extended upon separation from 3 months to 18 months, which resulted in additional incremental stock-based compensation of $0.5 million.
	In February 2013, we amended stock options held by our former CEO to extend the post-termination exercise period for the former CEO’s outstanding vested options from 18 months to 20 months, which resulted in additional incremental stock-based compensation of $157,000 in the first quarter of 2013.
	Employee stock-based compensation expense recognized was calculated based on awards ultimately expected to vest and has been reduced for estimated forfeitures. Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. Total stock-based compensation expense recognized was as follows:
	(in thousands)	YEARS ENDED DECEMBER 31
		2013			2012			2011
	Research and development	$	968		$	705		$	668
	General and administrative		1,178			1,016			2,259
	Total	$	2,146		$	1,721		$	2,927
	The fair value of each stock option was estimated using the Black-Scholes option-pricing model based on the date of grant of such stock option with the following assumptions:
		Options									ESPP
		Year Ended December 31,									Year Ended December 31,
		2013			2012			2011			2013			2012		2011
	Expected term (years)		5.0-6.1			5.0-6.1			5.3-6.1			0.5			—		—
	Expected volatility		85	%		85	%		85	%		62	%		—		—
	Risk-free interest rate		0.8-2.0	%		0.6-1.1	%		1.3-2.6	%		0.1	%		—		—
	Expected dividend yield		0	%		0	%		0	%		0	%		—		—
	The expected term of options granted represents the period of time that options granted are expected to be outstanding and was determined by calculating the midpoint between the date of vesting and the contractual life of each option. The expected term of the ESPP rights equals to the six-month look-back period. Volatility is based on the average historical volatility of a peer group of public companies over the expected term. The peer group was selected on the basis of operational and economic similarity with our principal business operations. The risk-free interest rate for the expected term of the options is based on the U.S. Treasury yield curve with a maturity equal to the expected term in effect at the time of grant. We have not paid, and do not anticipate paying, cash dividends on our shares of common stock; therefore, the expected dividend yield is zero.
	The weighted-average grant-date fair value per share of stock options granted during the years ended December 31, 2013, 2012 and 2011, was $5.05, $4.06 and $6.03 per share, respectively. The total intrinsic value of options exercised during the years ended December 31, 2013, 2012 and 2011, was $1.1 million, $0.3 million and $0.2 million, respectively. As of December 31, 2013, there was $4.3 million of total unrecognized compensation expense related to nonvested employee and director stock options that is expected to be recognized over a weighted-average period of 2.7 years.

Employee_Benefit_Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2013
Postemployment Benefits [Abstract]	'
Employee Benefit Plans	'
	8. Employee Benefit Plans
	We sponsor a 401(k) plan that stipulates that eligible employees can elect to contribute to the 401(k) plan, subject to certain limitations, up to the lesser of the statutory maximum or 100% of eligible compensation on a pre-tax basis. Through December 2013, we have not elected to match employee contributions as permitted by the plan. We pay the administrative costs for the plan.

Collaborative_Research_and_Dev

Collaborative Research and Development Agreements	12 Months Ended
	Dec. 31, 2013
Organization Consolidation And Presentation Of Financial Statements [Abstract]	'
Collaborative Research and Development Agreements	'
	9. Collaborative Research and Development Agreements
	Pfizer Inc.
	In May 2008, we entered into a discovery research collaboration and license agreement with Pfizer Inc. (Pfizer). Under the terms of the agreement, we received an upfront technology access payment of $7.5 million in May 2008 and received a $7.5 million milestone payment in August 2008. In addition, Pfizer provided for research funding over the research program term, and we received $3.8 million of such research funding in the year ended December 31, 2011.
	The $7.5 million upfront technology access payment was recorded as deferred revenue and was recognized over the three-year research period under the agreement. The $7.5 million milestone payment was determined to not represent a substantive, at-risk milestone at the time we entered into the collaboration and, therefore, was recognized over the three-year research period under the agreement.
	In connection with the agreement, Pfizer purchased 1,538,123 shares of our Series A-2 convertible preferred stock at a price of $22.76 per share, resulting in net cash proceeds to us of $35.0 million. As a result of the purchase of shares of our Series A-2 convertible preferred stock, in May 2008, Pfizer became a related party to us. We determined that the purchase price of $22.76 per share exceeded the estimated fair value of the Series A-2 convertible preferred stock by $10.9 million and, therefore, recorded the $10.9 million as revenue over the three-year research period.
	The agreement expired at the end of the research term in 2011. Total revenue recognized under this arrangement was $7.2 million for the year ended December 31, 2011.
	Fast Forward LLC
	In May 2010, we entered into a sponsored research agreement with Fast Forward LLC (Fast Forward), pursuant to which Fast Forward will fund the development of our preclinical-stage therapeutic candidate for treatment of multiple sclerosis. Under the agreement and subject to advancement of the therapeutic candidate, Fast Forward is obligated to pay us an aggregate amount of up to $1.0 million, of which $0.6 million was received in June 2010. Revenue will be recognized based on expenses incurred by us in the conduct of the research set forth in the agreement. Revenues attributable to research and development activities performed under the agreement were $0.1 million for each of the years ended December 31, 2013, 2012 and 2011. As of December 31, 2013 and 2012, we had deferred revenue relating to this research agreement of $0.1 million and $0.3 million, respectively. In addition, we are obligated to make certain contingent payments to Fast Forward, dependent solely on the results of the research and development having future economic benefit. Future contingent payments to Fast Forward consist of a $0.2 million milestone payment upon the administration of a certain compound to the first patient in a Phase III trial in multiple sclerosis and double-digit royalties, up to $2.8 million in the aggregate, based on net sales after commercialization in certain jurisdictions, if any, of such compounds.
	The agreement will terminate upon the expiration of the royalty terms of any products that result from the collaboration. In addition, Fast Forward may terminate this agreement for certain scientific or commercial reasons with advance written notice, and either party may terminate this agreement for the other party’s uncured material breach or bankruptcy.
	GlaxoSmithKline
	Muscle Disorders Discovery Collaboration
	In July 2010, we entered into a research collaboration and license agreement with GlaxoSmithKline LLC (GSK US) to identify potential drug targets and drug candidates to treat skeletal muscle diseases. Under the terms of the agreement, we received an upfront technology access payment of $7.0 million in August 2010. The $7.0 million upfront technology access payment was recorded as deferred revenue and was being recognized over the initial three-year research period under the agreement. In addition, GSK US provides for research funding over the research program term.
	In May 2011, we amended the agreement to expand the research plan in scope and duration to include an additional cell-based screen and an in vivo screen using our RIPPS technology. Under the amendment, GSK US agreed to provide an additional $6.3 million of research funding over a three-year research program term beginning on the date of the expansion. We received $1.5 million, $4.2 million and $3.6 million of research funding in the years ended December 31, 2013, 2012 and 2011, respectively, related to all research being performed under the GSK US collaboration. Due to this amendment, in May 2011 we revised our estimate of our substantive performance period under this collaboration to extend through the end of this additional research term and began recognizing the remaining unamortized portion of the upfront payment over this revised period into May 2014.
	We are eligible to receive certain option and selection payments related to targets identified in the collaboration, payments for the achievement of certain development activities, and royalties on the sales of products related to targets GSK US selects for exclusive development, if any.
	We are eligible to receive up to $1.8 million of preclinical milestone payments for each screening assay when a target is claimed or selected for further development. Substantive uncertainty exists as to whether any of these milestones will be achieved because of the numerous variables that may affect our ability to identify targets that GSK US would be interested in further evaluating or with respect to which GSK US would develop products. In accordance with ASU No. 2010-17, we concluded that these milestones under the agreement with GSK are substantive and will be accounted for under the milestone method of revenue recognition.
	In accordance with ASU No. 2010-17, we determined that the remaining contingent payments under the agreement with GSK US 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 agreement with GSK US do not meet the definition of a milestone under ASU 2010-17 because the achievement of these events is solely dependent on GSK US’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 this arrangement. If there are no remaining performance obligations under the arrangement at the time the contingent payment is triggered, the contingent payment would be recognized as revenue in full upon the triggering event.
	In connection with the agreement, GSK US purchased 329,597 shares of our Series A-2 convertible preferred stock at a price of $22.76 per share, resulting in net cash proceeds to us of $7.5 million. We determined that the purchase price of $22.76 per share exceeded the estimated fair value of the Series A-2 convertible preferred stock by $3.0 million and, therefore, recorded the $3.0 million as revenue in the same manner as the upfront technology access payment.
	In December 2012, GSK US selected a protein therapeutic target for further evaluation. The related milestone payment of $0.3 million was received in 2013 and was recorded as accounts receivable as of December 31, 2012. In September 2013, we and GSK US entered into an agreement to extend the evaluation period for this protein therapeutic target by approximately eight months. In connection with the extension of the evaluation period, GSK US paid a $0.2 million extension fee. We are recognizing the $0.2 million extension fee over the eight-month extension period.
	In October 2013, GSK US exercised its right to reserve for further evaluation several protein therapeutic targets for muscle diseases that we discovered in this agreement with GSK US. In connection with reserving these targets for further evaluation, GSK US paid us a selection fee of $0.3 million in 2013.
	Total revenue recognized under this arrangement was $5.8 million, $5.8 million and $5.2 million for the years ended December 31, 2013, 2012 and 2011, respectively. As of December 31, 2013 and 2012, we had deferred revenue relating to this collaboration agreement of $1.9 million and $5.7 million, respectively.
	The agreement will terminate upon the expiration of the royalty terms of any products that incorporate or target a protein exclusively licensed under the collaboration. In addition, GSK US may terminate this agreement at any time with advance written notice, and either party may terminate this agreement with written notice for the other party’s material breach if such party fails to cure the breach or upon certain insolvency events.
	Respiratory Diseases Discovery Collaboration
	In April 2012, we entered into a research collaboration and license agreement with Glaxo Group Limited (GSK UK) to identify new therapeutic approaches to treat refractory asthma and chronic obstructive pulmonary disease (COPD) function with a particular focus on identifying novel protein therapeutics and antibody targets. We plan to conduct up to six customized cell-based screens of our protein library under this agreement. The four-year research term will end in April 2016. Under the terms of the agreement, GSK UK paid us an upfront technology access payment of $7.5 million in April 2012.
	We applied ASU No. 2009-13, Multiple-Deliverable Revenue Arrangements, in evaluating the appropriate accounting for this agreement. In accordance with this guidance, we concluded that the arrangement should be accounted for as a single unit of accounting and that the arrangement consideration should be recognized in the same manner as the final deliverable, which is the research service. The $7.5 million upfront technology access payment was recorded as deferred revenue and is being recognized over the initial four-year research period under the agreement. In addition, GSK UK agreed to pay us $10.5 million of research funding over the research program term. We received $3.4 million and 1.3 million of research funding in the years ended December 31, 2013 and 2012, respectively, related to all research being performed under the GSK UK discovery collaboration.
	We are eligible to receive certain option and selection payments, payments for the achievement of certain development activities, and royalties on the sales of products related to targets GSK UK selects for exclusive development, if any.
	We are eligible to receive up to $1.8 million of preclinical milestone payments for each screen assay when a target is claimed or selected for further development. In addition, prior to the time GSK UK exercises its right to obtain an exclusive worldwide license to a protein target, we and GSK UK will discuss and agree on Track 1 Targets, which GSK UK will have sole responsibility for the further development and commercialization of products that incorporate or target the protein targets, and Track 2 Targets, which we will develop biologics that incorporate or target the protein targets through to clinical proof of mechanism in either a Phase 1 clinical trial or Phase 2 clinical trial. We and GSK UK will take into consideration each party’s available resources and capabilities at the time in deciding which protein targets will be Track 1 Targets or Track 2 Targets, but subject to each party’s general right to alternate in such selection with GSK UK have the right to first select. For each Track 2 Target, we are eligible to receive a $4.0 million milestone payment upon initiation of the first GLP toxicology study, a $6.5 million milestone payment upon the initiation of Phase 1 clinical trial and a $11.0 million milestone payment upon the initiation of Phase 2 clinical trial. We are also eligible to receive a $14.0 million option exercise milestone if GSK UK exercises its option to develop the Track 2 Target prior to the initiation of Phase 2 clinical trial or a $23.0 million option exercise milestone if GSK UK exercises after the initiation of Phase 2 clinical trial for the Track 2 Targets. Substantive uncertainty exists at the inception of the agreement as to whether any of these milestones will be achieved because of the numerous variables that may affect our ability to identify targets that GSK UK would be interested in further evaluating or with respect to which GSK UK would develop products. In accordance with ASU No. 2010-17, we concluded that these milestones under the agreement with GSK UK are substantive and will be accounted for under the milestone method of revenue recognition.
	In accordance with ASU No. 2010-17, we determined that the remaining contingent payments under the agreement with GSK UK 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 agreement with GSK UK do not meet the definition of a milestone under ASU 2010-17 because the achievement of these events is solely dependent on GSK UK’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 this arrangement. If there are no remaining performance obligations under the arrangement at the time the contingent payment is triggered, the contingent payment would be recognized as revenue in full upon the triggering event.
	In connection with the agreement, GSK UK purchased 381,693 shares of our Series A-3 convertible preferred stock at a price of $26.20 per share, resulting in net cash proceeds to us of $10.0 million. We determined that the purchase price of $26.20 per share exceeded the estimated fair value of the Series A-3 convertible preferred stock by $3.1 million and, therefore, recorded the $3.1 million as deferred revenue to be recognized initially over the four-year research period.
	Total revenue recognized under this arrangement was $5.6 million and $3.2 million for the years ended December 31, 2013 and 2012, respectively. As of December 31, 2013 and 2012, we had deferred revenue relating to this collaboration agreement of $6.8 million and $8.8 million, respectively. Additionally, GSK UK is obligated to reimburse us for certain specialized research and development costs associated with the screens under the agreement. As of December 31, 2013 and 2012, the receivable from GSK UK under the agreement related to such costs was $0.1 million and zero, respectively.
	The agreement will terminate upon the expiration of the royalty terms of any products that incorporate or target a protein exclusively licensed under the collaboration. In addition, GSK UK may terminate this agreement at any time with advance written notice, and either party may terminate this agreement with written notice for the other party’s material breach if such party fails to cure the breach or immediately in the case of failure to comply with certain anti-bribery and anti-corruption policies or upon certain insolvency events.
	Human Genome Sciences, Inc.
	In March 2011, we entered into a license and collaboration agreement with Human Genome Sciences, Inc. (HGS), which was acquired by GlaxoSmithKline (GSK) in 2012 and we refer to HGS as GSK-HGS. Pursuant to the agreement we granted GSK-HGS an exclusive license to develop and commercialize our FP-1039 product and other FGFR1 fusion proteins for multiple cancers in the United States, the European Union and Canada. Under the terms of the agreement, GSK-HGS paid us an upfront license fee of $50 million. We received full payment of the $50 million upfront license fee in March 2011. The agreement also calls for tiered double-digit percentage royalty payments on net sales. GSK-HGS has exclusive rights to develop and commercialize FP-1039 for all indications in the United States, the European Union and Canada. We have an option to co-promote FP-1039 in the United States, and retain development and commercialization rights in territories outside the United States, the European Union and Canada.
	We applied ASU No. 2009-13, Multiple-Deliverable Revenue Arrangements, in evaluating the appropriate accounting for this agreement. In accordance with this guidance, we identified the initial license, associated technology transfer and services for the conduct of the then-concluding FP-1039 Phase 1 clinical trial as substantive deliverables under this agreement. However, since all of the deliverables were fully delivered by December 31, 2011, the $50 million upfront license fee associated with the deliverables was entirely recognized as revenue in 2011.
	Additionally, GSK-HGS is obligated to reimburse us for all future research and development costs associated with FP-1039 incurred by us in the conduct of research and development activities on behalf of GSK-HGS. At the time we entered into the FP-1039 license, we agreed to perform services for the conduct of the then-concluding Phase 1 clinical trial. We also elected to conduct a Phase 2 clinical trial of FP-1039 in endometrial cancer for which we were reimbursed by GSK-HGS. The Phase 2 clinical trial was terminated in January 2012 and we are no longer conducting any activities with respect to this trial. Additionally, GSK-HGS is obligated to pay us for the costs of other FP-1039 related research and development activities we elect to undertake on behalf of GSK-HGS. Revenue from GSK-HGS related to these development costs associated with FP-1039 is recognized as we incur these costs. For the years ended December 31, 2013, 2012 and 2011, we recognized $0.1 million, $0.9 million and $2.4 million, respectively, in revenue from GSK-HGS related to development costs associated with FP-1039. As of December 31, 2013 and 2012, the receivable from GSK-HGS under the agreement related to such costs was zero and $0.1 million, respectively.
	GSK-HGS is obligated to pay us certain amounts contingent upon the achievement of pre-specified development, regulatory and commercial criteria, which could total approximately $435 million. We determined that these contingent payments will not be accounted for under the milestone method of revenue recognition as the events that trigger these payments under the agreement with GSK-HGS do not meet the definition of a milestone under ASU 2010-17 because the achievement of these milestones is solely dependent on GSK-HGS’s performance. Revenue from these contingent payments will be recognized if and when such payments become due, subject to satisfaction of all the criteria necessary to recognize revenue at that time, because we do not have any outstanding performance obligations under this arrangement.
	The agreement will terminate upon the expiration of the royalty terms of any products that result from the collaboration. In addition, GSK-HGS may terminate this agreement at any time with advance written notice, and either party may terminate this agreement for the other party’s material breach if such party fails to cure the breach or upon certain insolvency events.
	UCB Pharma S.A.
	In March 2013, we and UCB Pharma, S.A. (UCB) entered into a research collaboration and license agreement to identify potential biologics targets and therapeutics in the areas of fibrosis-related inflammatory diseases and central nervous system disorders. We plan to conduct five customized cell-based and in vivo screens of our protein library under this agreement. We currently expect to complete our initial research activities under this agreement by March 2016. Upon the completion of those research activities, UCB has up to a two-year evaluation period during which we may be obligated to perform additional services at the request of UCB.
	We applied ASU No. 2009-13, Multiple-Deliverable Revenue Arrangements, in evaluating the appropriate accounting for this agreement. In accordance with this guidance, we concluded that we should account for the arrangement as a single unit of accounting and recognize the arrangement consideration in the same manner as the final deliverable, which is research service.
	Under the terms of the agreement, UCB paid us an upfront payment of $6.0 million in March 2013. In addition, we received $2.2 million of a $6.6 million technology access fee in March 2013. The remaining $4.4 million technology access fee is due in two equal installments on the first and second anniversaries of this agreement. UCB also agreed to pay us $2.0 million of research funding during the second and the third years of the research program term. We recorded the $6.0 million upfront payment and $2.2 million technology access payment as deferred revenue, which we will recognize over the initial five-year research period under the agreement.
	We are eligible to receive certain evaluation and selection fees and contingent payments with respect to each protein target that UCB elects to obtain an exclusive license, and royalties on the sales of products related to such targets, if any.
	We are eligible to receive up to $0.4 million of target evaluation and selection fees with respect to each target we offer to UCB in the collaboration. Substantive uncertainty exists at the inception of the agreement as to whether any of these fees will be received because of the numerous variables that may affect our ability to identify targets that UCB would be interested in further evaluating or with respect to which UCB would develop products. In accordance with ASU No. 2010-17, we concluded that these fees under the agreement with UCB are substantive and will be accounted for under the milestone method of revenue recognition.
	In accordance with ASU No. 2010-17, we determined that the remaining contingent payments under the agreement with UCB 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 agreement with UCB do not meet the definition of a milestone under ASU 2010-17 because the achievement of these events solely depends on UCB’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 this arrangement. If we have no remaining performance obligations under the arrangement at the time the contingent payment is triggered, we would recognize the contingent payment as revenue in full upon the triggering event.
	For the year ended December 31, 2013, we recognized $2.2 million of revenue under this arrangement. As of December 31, 2013, we have deferred revenue relating to this collaboration agreement of $6.2 million. Additionally, UCB is obligated to reimburse us for certain specialized research and development costs associated with the screens under the agreement. As of December 31, 2013, the receivable from UCB under the agreement related to such costs was $0.2 million.
	The agreement will terminate upon the expiration of the royalty terms of any products that incorporate or target a protein exclusively licensed under the collaboration. In addition, UCB may terminate this agreement at any time with advance written notice, and either party may terminate the agreement with written notice for the other party’s material breach if such party fails to cure the breach or upon certain insolvency events.

Acquired_Technologies

Acquired Technologies	12 Months Ended
	Dec. 31, 2013
Research And Development [Abstract]	'
Acquired Technologies	'
	10. Acquired Technologies
	Galaxy Biotech, LLC
	In December 2011, we entered into an exclusive license agreement with Galaxy Biotech, LLC (Galaxy) for the development, manufacturing, and commercialization of certain anti-FGFR2b (fibroblast growth factor receptor 2) monoclonal antibodies. Under the terms of the agreement, we agreed to pay Galaxy an upfront license payment of $3.0 million. The upfront payment was paid in two equal installments in January 2012 and July 2012. As we had full access to the technology and materials upon execution of the agreement, the lead compound is in an early stage of development, and the underlying technology has no alternative future uses, the entire upfront payment was recorded to research and development expenses in our statement of operations for the year ended December 31, 2011. We are also required to make additional payments based upon the achievement of certain intellectual property, development, regulatory, and commercial milestones, as well as royalties on future net sales of products resulting from development of this purchased technology, if any.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2013
Income Tax Disclosure [Abstract]	'
Income Taxes	'
	11. Income Taxes
	No income tax benefit or expense was recorded for the years ended December 31, 2013, 2012 and 2011.
	A reconciliation of the federal statutory income tax rate to our effective income tax rate is as follows:
	(in thousands)	YEARS ENDED DECEMBER 31,
		2013			2012			2011
	Federal statutory income tax rate	$	(10,105	)	$	(9,658	)	$	6,899
	Nondeductible stock compensation		455			386			414
	Nontaxable equity premiums		(532	)		(452	)		(825	)
	Deferred tax assets (utilized) not benefitted		10,338			9,750			(6,527	)
	Other permanent items		(156	)		(26	)		39
	(Benefit) from income taxes	$	—		$	—		$	—
	The tax effects of temporary differences and carryforwards that give rise to significant portions of the deferred tax assets consist of the following (in thousands):
		YEARS ENDED DECEMBER 31,
		2013			2012			2011
	Net operating loss carryforwards	$	59,552		$	48,613		$	37,905
	Research and development credit		6,564			5,372			5,218
	Reserves and accruals		5,936			6,020			5,204
	Total deferred tax assets		72,052			60,005			48,327
	Deferred tax liability		—			—			—
	Net deferred tax asset		72,052			60,005			48,327
	Less: valuation allowance		(72,052	)		(60,005	)		(48,327	)
	Net deferred tax assets	$	—		$	—		$	—
	Realization of deferred tax assets is dependent upon future taxable income, if any, the amount and timing of which are uncertain. Accordingly, net deferred tax assets have been fully offset by a valuation allowance. Our valuation allowance increased by approximately $12.1 million, increased by $11.7 million and decreased by $7.2 million during 2013, 2012 and 2011 respectively. We have established a full valuation allowance against our deferred tax assets due to the uncertainty surrounding the realization of such assets. We evaluate on a periodic basis the recoverability of deferred tax assets and the need for a valuation allowance. At such time that it is determined that it is more likely than not that the deferred tax assets are realizable, the valuation allowance will be reduced.
	At December 31, 2013, we had approximately $142.5 million and $168.3 million of federal and state net operating loss carryforwards, respectively, available to offset future taxable income. The net operating loss carryforwards begin to expire in 2024 for federal and 2015 for state purposes. We also had approximately $5.4 million and $4.0 million of federal and state tax credits, respectively, available to offset future tax. These credits begin to expire in 2023 for federal purposes, and state research and development tax credits can be carried forward indefinitely.
	Utilization of the net operating loss and credit carryforwards may be subject to substantial annual limitation due to ownership change provisions of the Internal Revenue Code of 1986 and similar state provisions. The annual limitation may result in the expiration of net operating losses and credits before utilization. To the extent net operating loss carryforwards, when realized, relate to non-qualified stock option deductions, the resulting benefits will be credited to stockholders’ equity.
	As of December 31, 2013 and 2012, we had no accrued interest or penalties related to income taxes, and no such interest and penalties have been incurred through December 31, 2013. As of December 31, 2013, no significant increases or decreases are expected to our uncertain tax positions within the next 12 months. A reconciliation of our unrecognized tax benefits for the years ended December 31, 2013, 2012 and 2011, is as follows:
	(in thousands)	UNRECOGNIZED
		INCOME TAX
		BENEFITS
	Balance as of January 1, 2011	$	1,313
	Additions for current year tax positions		144
	Balance as of December 31, 2011		1,457
	Additions for current year tax positions		78
	Balance as of December 31, 2012		1,535
	Deductions for prior year tax positions		27
	Additions for current year tax positions		219
	Balance as of December 31, 2013	$	1,781
	We file U.S. and state income tax returns with varying statutes of limitations. The tax years from inception in 2001 forward remain open to examination due to the carryover of unused net operating losses and tax credits. We have no ongoing tax examinations by tax authorities at this time.

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2013
Commitments And Contingencies Disclosure [Abstract]	'
Commitments and Contingencies	'
	12. Commitments and Contingencies
	Indemnifications
	As permitted under Delaware law and in accordance with our bylaws, we have agreed to indemnify our officers and directors for certain events or occurrences, subject to certain limits, while the officer or director is or was serving at the our request in such capacity. The term of the indemnification period is equal to the officer’s or director’s lifetime.
	The maximum amount of potential future indemnification is unlimited; however, we currently hold director and officer liability insurance. This insurance limits our exposure and may enable us to recover a portion of any future amounts paid. We believe that the fair value of these indemnification obligations is minimal. Accordingly, we have not recognized any liabilities relating to these obligations for any period presented.
	We have certain agreements with service providers and other parties with which we do business that contain indemnification provisions pursuant to which we have agreed to indemnify the party against certain types of third-party claims. We accrue for known indemnification issues when a loss is probable and can be reasonably estimated. We would also accrue for estimated incurred but unidentified indemnification issues based on historical activity. As we have not incurred any indemnification losses to date, there were no accruals for or expenses related to indemnification issues for any period presented.

Selected_Quarterly_Financial_I

Selected Quarterly Financial Information	12 Months Ended
	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]	'
Selected Quarterly Financial Information	'
	13. Selected Quarterly Financial Information (Unaudited)
	The following amounts are in thousands, except per share amounts:
		Quarter Ended
	Quarterly Results of Operations	March 31,			June 30,			September 30,			December 31,
		2013			2013			2013			2013
		(Unaudited)
		(In thousands, except per share amounts)
	Revenue	$	2,975		$	3,549		$	3,482		$	3,785
	Net loss		(7,047	)		(7,274	)		(7,234	)		(7,317	)
	Basic and diluted net loss per share		(5.73	)		(5.82	)		(2.74	)		(0.43	)
		Quarter Ended
	Quarterly Results of Operations	March 31,			June 30,			September 30,			December 31,
		2012			2012			2012			2012
		(Unaudited)
		(In thousands, except per share amounts)
	Revenue	$	2,014		$	2,183		$	2,862		$	2,924
	Net loss		(8,081	)		(6,843	)		(5,858	)		(6,813	)
	Basic and diluted net loss per share		(6.92	)		(5.72	)		(4.85	)		(5.59	)
	Basic and diluted net loss per share is computed independently for each of the quarters presented. Therefore, the sum of quarterly basic and diluted per share amounts may not equal annual basic and diluted net loss per share amounts.

Subsequent_Events

Subsequent Events	12 Months Ended
	Dec. 31, 2013
Subsequent Events [Abstract]	'
Subsequent Events	'
	14. Subsequent Events
	Financing
	In February 2014, we completed a public offering of 3,450,000 shares of our common stock, which includes shares we issued pursuant to our underwriters’ exercise of their over-allotment option, and received net proceeds of $40.0 million, after underwriting discounts, commissions and estimated offering expenses.
	Bristol-Myers Squibb Company Research Collaboration and License Agreement
	On March 14, 2014, we entered into a research collaboration and license agreement 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 agreement, we granted BMS an exclusive, worldwide license to research, develop and commercialize products directed towards targets in two undisclosed immune checkpoint pathways. BMS will have an option to take exclusive licenses to additional interactive proteins we may identify in these checkpoint pathways during the course of our collaboration.
	We are entitled to receive an upfront payment of $20 million from BMS in connection with our entry into the agreement and will receive $9.5 million in research funding over the course of the three-year research term. BMS may extend the research term for two additional one-year periods on a year-by-year basis. We will be eligible to receive up to $240 million per collaboration target in specified developmental, regulatory and commercialization contingent payments and up to $60 million in sales-based contingent payments per collaboration product. We are also entitled to tiered mid-single digit to low double-digit percentage royalty payments on net sales of each collaboration product, subject to reduction in certain circumstances. In connection with the agreement, 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.

Organization_and_Summary_of_Si1

Organization and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
Initial Public Offering	'
	Initial Public Offering
	In September 2013, we completed our initial public offering of shares of our common stock, or IPO, pursuant to which we issued 5,520,000 shares of common stock, which includes shares we issued pursuant to our underwriters’ exercise of their over-allotment option, and received net proceeds of $63.8 million, after underwriting discounts, commissions and offering expenses. In addition, in connection with the completion of our IPO, all convertible preferred stock converted into common stock.
Use of Estimates	'
	Use of Estimates
	The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ materially from those estimates.
Reverse Stock Split	'
	Reverse Stock Split
	On September 4, 2013, the Company effected a 1-for-12.3 reverse stock split. All information in this report relating to the number of shares, price per share and per share amounts of stock gives retroactive effect to the 1-for-12.3 reverse stock split of the Company’s stock.
Reclassifications	'
	Reclassifications
	Certain prior period amounts have been reclassified 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 the balance sheets, and made related conforming reclassifications on the statement of cash flows.
Cash and Cash Equivalents	'
	Cash and Cash Equivalents
	We consider all highly liquid investments purchased with original maturities of three months or less at the date of purchase to be cash equivalents. Cash equivalents are stated at fair value.
Marketable Securities	'
	Marketable Securities
	All marketable securities have been classified as “available for sale” and are carried at fair value, based upon quoted market prices. We consider our available-for-sale portfolio as available for use in current operations. Accordingly, we may classify certain investments as short-term marketable securities, even though the stated maturity date may be one year or more beyond the current balance sheet date. Unrealized gains and losses, net of any related tax effects, are excluded from earnings and are included in other comprehensive income and reported as a separate component of stockholders’ deficit until realized. Realized gains and losses and declines in value judged to be other than temporary, if any, on available-for-sale securities are included in other income (expense), net. The cost of securities sold is based on the specific-identification method. The amortized cost of securities is adjusted for amortization of premiums and accretion of discounts to maturity. Interest on short-term investments is included in interest income. In accordance with our investment policy, management invests to diversify credit risk and only invests in debt securities with high credit quality, including U.S. government securities, and does not invest in mortgage-backed securities or mortgage loans.
	We periodically evaluate whether declines in the fair value of our investments below their cost are other than temporary. The evaluation includes consideration of the cause of the impairment, including the creditworthiness of the security issuers, the number of securities in an unrealized loss position, the severity and duration of the unrealized losses, whether we have the intent to sell the securities, and whether it is more likely than not that we will be required to sell the securities before the recovery of their amortized cost basis. If we determine that the decline in fair value of an investment is below its accounting basis and this decline is other than temporary, we would reduce the carrying value of the security we hold and record a loss for the amount of such decline. We have not recorded any realized losses or declines in value judged to be other than temporary on our investments in debt securities.
Restricted Cash	'
	Restricted Cash
	We had a certificate of deposit that served as collateral under a revolving credit agreement. Amounts related to the certificate of deposit were reported as short-term restricted cash and totaled $38,000 at December 31, 2011. In March 2012, we terminated this revolving credit agreement, and the certificate of deposit was refunded to us in 2012.
Concentrations of Credit Risk	'
	Concentrations of Credit Risk
	Financial instruments that potentially subject us to significant concentrations of credit risk consist primarily of cash and cash equivalents and marketable securities. Cash and cash equivalents and marketable securities are invested through banks and other financial institutions in the United States. Such deposits in the United States may be in excess of insured limits.
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. For our marketable securities, we review trading activity and pricing as of the measurement date. When sufficient quoted pricing for identical securities is not available, we use market pricing and other observable market inputs for similar securities obtained from various third-party data providers. These inputs either represent quoted prices for similar assets in active markets or have been derived from observable market data; 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.
	Level 1 securities consist of highly liquid money market funds and U.S. Treasury securities. The fair value of Level 1 assets has been determined using quoted prices in active markets for identical assets. Level 2 securities consist of U.S. government agency securities and were measured at fair value using Level 2 inputs. We review trading activity and pricing for these 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, were derived from observable market data, or, if not directly observable, were derived from or corroborated by other observable market data. There were no transfers between Level 1 and Level 2 securities in the periods presented.
	In certain cases where there is limited activity or less transparency around inputs to valuation, securities are classified as Level 3 within the valuation hierarchy. As of December 31, 2012, our Level 3 liability consisted of a preferred stock warrant liability that we measured at estimated fair value. Prior to our IPO in September 2013, we had outstanding warrants which were classified as a liability and remeasured to fair value each reporting period. We measured the estimated fair value of the preferred stock warrant liability using the Black-Scholes option-pricing model. Inputs used to determine estimated fair value include the estimated fair value of the underlying stock at the valuation measurement date, the remaining contractual term of the warrants, risk-free interest rates, expected dividends, and the expected volatility of the price of the underlying stock. In connection with the completion of the Company’s IPO in September 2013, substantially all of the warrants were automatically net exercised for a total of 4,376 shares, pursuant to the terms of the warrants. As a result of the net exercises, we recorded an $83,000 gain related to the change in fair value as part of other income, net on our statement of operations and reclassified the fair value of $57,000 to permanent equity. These warrants were remeasured using the intrinsic value of the warrant and the net settlement value based on the $13.00 per share IPO price. The remaining outstanding warrant to purchase Series A convertible preferred stock converted into a warrant to purchase 2,304 shares of common stock at $12.30 per share. We remeasured the fair value of these remaining warrants through the date of the conversion to a common stock warrant and we recorded a $3,000 loss related to the change in fair value as part of other income, net on our statement of operations and reclassified the fair value of $6,000 to permanent equity. The common stock warrant was automatically net exercised for a total of 768 shares on January 26, 2014. The Level 3 liability that is measured at estimated fair value on a recurring basis consists of the preferred stock warrant liability. The estimated fair value of the outstanding preferred stock warrant liability is measured using the Black-Scholes option-pricing model. Inputs used to determine estimated fair value include the estimated fair value of the underlying stock at the valuation measurement date, the remaining contractual term of the warrants, risk-free interest rates, expected dividends, and the expected volatility of the price of the underlying stock.
	The following table summarizes, for assets and the liability recorded at fair value, the respective fair value and the classification by level of input within the fair value hierarchy defined above (in thousands):
			DECEMBER 31, 2013
						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		$	—
			DECEMBER 31, 2012
						BASIS OF FAIR VALUE MEASUREMENTS
			TOTAL			LEVEL 1			LEVEL 2			LEVEL 3
	Assets
	Money market funds		$	6,910		$	6,910		$	—		$	—
	U.S. Treasury securities			3,577			3,577			—			—
	U.S. government agency securities			23,047			—			23,047			—
	Total cash equivalents and marketable securities		$	33,534		$	10,487		$	23,047		$	—
	Liability
	Preferred stock warrant liability		$	563		$	—		$	—		$	563
	The change in the estimated fair value of the preferred stock warrant liability is summarized below (in thousands):
			YEARS ENDED DECEMBER 31
			2013			2012			2011
	Balance, beginning of year		$	563		$	682		$	622
	Change in fair value recorded in other income (expense), net			(500	)		(119	)		60
	Exercises			(57	)		—			—
	Conversion of preferred stock warrant to common stock warrant and reclassification to permanent equity			(6	)		—			—
	Balance, end of year		$	—		$	563		$	682
	The fair value of the above warrants was determined using the Black-Scholes valuation model with the following assumptions:
			DECEMBER 31
			2012			2011
	Risk-free interest rate			0.2%—0.3%			0.1%—0.4%
	Remaining contractual term (years)			2.1			3
	Volatility			85.00%			85.00%
Property and Equipment	'
	Property and Equipment
	Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful lives of the assets, ranging from three to five years. Leasehold improvements are amortized over the shorter of their estimated useful lives or the related lease term.
Impairment of Long-Lived Assets	'
	Impairment of Long-Lived Assets
	Long-lived assets include property and equipment. The carrying value of long-lived assets is reviewed for impairment whenever events or changes in circumstances indicate that the assets may not be recoverable. An impairment loss is recognized when the total estimated future cash flows expected to result from the use of the asset and its eventual disposition are less than the carrying amount. Through December 31, 2013, there have been no such impairment losses.
Preferred Stock Warrant Liability	'
	Preferred Stock Warrant Liability
	Freestanding warrants for shares that are either putable or redeemable are classified as liabilities on the balance sheet at fair value. Therefore, the freestanding warrants that give the holders the right to purchase our convertible preferred stock are liabilities that are recorded at estimated fair value. At the end of each reporting period, changes in fair value during the period are recorded as a component of other income (expense), net.
	We adjusted the liability for changes in the estimated fair value of the warrants until the earlier of the exercise or expiration of the warrants to purchase shares of convertible preferred stock or the completion of a liquidation event, including the completion of an initial public offering, at which time the liabilities were reclassified to stockholders’ deficit.
Revenue Recognition	'
	Revenue Recognition
	We recognize revenue when all of the following criteria are met: persuasive evidence of an arrangement exists; transfer of technology has been completed or services have been rendered; our price to the customer is fixed or determinable and collectability is reasonably assured.
	The terms of our collaborative research and development agreements include nonrefundable upfront and license fees, research funding, milestone and other contingent payments to us for the achievement of defined collaboration objectives and certain preclinical, clinical, regulatory and sales-based events, as well as royalties on sales of any commercialized products.
	Multiple-Element Revenue Arrangements. Our collaborations primarily represent multiple-element revenue arrangements. To account for these transactions, we determine the elements, or deliverables, included in the arrangement and determine which deliverables are separable for accounting purposes. We consider delivered items to be separable if the delivered items have stand-alone value to the customer. If the delivered items are separable, we allocate arrangement consideration to the various elements based on each element’s relative selling price. The identification of individual elements in a multiple-element arrangement and the estimation of the selling price of each element involve significant judgment, including consideration as to whether each delivered element has standalone value to the customer. We determine the estimated selling price for deliverables within each agreement using vendor-specific objective evidence (VSOE) of selling price, if available, or third party evidence of selling price if VSOE is not available, or our best estimate of selling price, if neither VSOE nor third party evidence is available. Determining the best estimate of selling price for a deliverable requires significant judgment. We use our best estimate of selling price to estimate the selling price for licenses to our proprietary technology, since we do not have VSOE or third party evidence of selling price for these deliverables.
	We recognize consideration allocated to an individual element when all other revenue recognition criteria are met for that element. Our multiple-element revenue arrangements generally include the following:
		•		Exclusive Licenses. The deliverables under our collaboration agreements generally include exclusive licenses to discover, develop, manufacture and commercialize compounds with respect to one or more specified targets. To account for this element of the arrangement, we evaluate whether the exclusive license has standalone value apart from the undelivered elements to the collaboration partner based on the consideration of the relevant facts and circumstances of each arrangement, including the research and development capabilities of the collaboration partner and other market participants. We recognize arrangement consideration allocated to licenses upon delivery of the license, if facts and circumstances indicate that the license has standalone value apart from the undelivered elements, which generally include research and development services. If facts and circumstances indicate that the delivered license does not have standalone value from the undelivered elements, we recognize the revenue as a combined unit of accounting.
	We have determined that some of our exclusive licenses lack standalone value apart from the related research and development services. In those circumstances we recognize collaboration revenue from non-refundable exclusive license fees in the same manner as the undelivered item(s), which is generally the period over which we provide the research and development services.
		•		Research and Development Services. The deliverables under our collaboration and license agreements generally include deliverables related to research and development services we perform on behalf of the collaboration partner. As the provision of research and development services is a part of our central operations and we are principally responsible for the performance of these services under the agreements, we recognize revenue on a gross basis for research and development services as we perform those services. Additionally, we recognize research funding related to collaborative research and development efforts as revenue as we perform or deliver the related services in accordance with contract terms as long as we will receive payment for such services upon standard payment terms.
	Milestone Revenue. Our collaboration and license agreements generally include contingent payments and milestone payments related to specified research, development and regulatory milestones and sales-based milestones. Research, development and regulatory contingent payments and milestone payments are typically payable under our collaborations when our collaborator claims or selects a target, or initiates or advances a covered product candidate in preclinical or clinical development, upon submission for marketing approval of a covered product with regulatory authorities, upon receipt of actual marketing approvals of a covered product or for additional indications, or upon the first commercial sale of a covered product. Sales-based milestones are typically payable when annual sales of a covered product reach specified levels.
	At the inception of each arrangement that includes milestone payments, we evaluate whether each milestone is substantive and at risk to both parties on the basis of the contingent nature of the milestone. We evaluate factors such as the scientific, regulatory, commercial and other risks that we must overcome to achieve the respective milestone, the level of effort and investment required to achieve the respective milestone and whether the milestone consideration is reasonable relative to all deliverables and payment terms in the arrangement in making this assessment.
	We have elected to adopt the Financial Accounting Standards Board Accounting Standards Update 2010-17, Revenue Recognition—Milestone Method, such that we recognize any payment that is contingent upon the achievement of a substantive milestone entirely in the period in which the milestone is achieved. A milestone is defined as an event that can only be achieved based in whole or in part on either our performance or the occurrence of a specific outcome resulting from our performance for which there is substantive uncertainty at the date the arrangement is entered into that the event will be achieved. Therefore, a milestone does not include events for which occurrence is contingent solely on the performance of a collaborative partner. To be substantive, a milestone must meet all the following criteria: the consideration receivable upon the achievement of the milestone is commensurate with either our performance to achieve the milestone or the enhancement of value of delivered items as a result of a specific outcome resulting from our performance to achieve the milestone, the consideration relates solely to past performance, and the consideration is reasonable relative to all of the deliverables and payment terms in the arrangement.
Research and Development Expenses	'
	Research and Development Expenses
	Research and development expenses consist of costs we incur for our own and for sponsored and collaborative research and development activities. Expenses we incur related to collaborative research and development agreements approximate the revenue recognized under these agreements. Research and development costs are expensed as incurred. Research and development costs consist of salaries and benefits, including associated stock-based compensation, laboratory supplies and facility costs, as well as fees paid to other entities that conduct certain research and development activities on our behalf. We estimate preclinical study and clinical trial expenses based on the services performed pursuant to contracts with research institutions and clinical research organizations that conduct and manage preclinical studies and clinical trials on our behalf based on actual time and expenses incurred by them. Further, we accrue expenses related to clinical trials based on the level of patient enrollment and activity according to the related agreement. We monitor patient enrollment levels and related activity to the extent reasonably possible and adjust estimates accordingly.
	We expense payments for the acquisition and development of technology as research and development costs if, at the time of payment: the technology is under development; is not approved by the U.S. Food and Drug Administration or other regulatory agencies for marketing; has not reached technical feasibility; or otherwise has no foreseeable alternative future use.
Stock-Based Compensation	'
	Stock-Based Compensation
	We recognize compensation expense using a fair-value-based method for costs related to all share-based payments, including stock options. Stock-based compensation cost related to employees and directors is measured at the grant date, based on the fair-value-based measurement of the award estimated using the Black-Scholes option-pricing model, and is recognized as expense over the requisite service period on a straight-line basis. We are required to estimate forfeitures at the time of grant and revise those estimates in subsequent periods if actual forfeitures differ from those estimates. We use historical data to estimate prevesting option forfeitures and record stock-based compensation expense only for those awards that are expected to vest. We recorded stock-based compensation expense for stock-based awards to employees and directors of approximately $2,067,000, $1,655,000 and $2,850,000 for the years ended December 31, 2013, 2012 and 2011, respectively.
	Options granted to individual service providers who are not employees or directors are accounted for at estimated fair value using the Black-Scholes option-pricing model and are subject to periodic remeasurement over the period during which the services are rendered. Stock-based compensation expense related to options granted to individual service providers who are not employees or directors was approximately $79,000, $66,000 and $77,000 for the years ended December 31, 2013, 2012 and 2011, respectively.
Income Taxes	'
	Income Taxes
	We account for income taxes using the liability method, under which deferred tax assets and liabilities are determined based on differences between financial reporting and tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. Valuation allowances are provided when the expected realization of the deferred tax assets does not meet the more-likely-than-not criteria. We are required to determine whether it is more likely than not that a tax position will be sustained upon examination by the appropriate taxing authorities before any part of the benefit can be recorded in the financial statements. It is our practice to recognize interest and penalties related to unrecognized tax benefits, if any, as a component of income tax expense.
Net (Loss) Income Per Share	'
	Net (Loss) Income Per Share
	We compute net (loss) income per share of common stock using the two-class method required for participating securities. We consider all series of our convertible preferred stock to be participating securities. In accordance with the two-class method, earnings allocated to these participating securities, which include participation rights in undistributed earnings, are subtracted from net income to determine total undistributed earnings to be allocated to common stockholders.
	Basic net (loss) income per common share is computed by dividing net (loss) income attributable to common stockholders by the weighted-average number of common shares outstanding during the period. All participating securities are excluded from basic weighted-average common shares outstanding. In computing diluted net (loss) income attributable to common stockholders, undistributed earnings are re-allocated to reflect the potential impact of dilutive securities, including stock options and warrants. Diluted net (loss) income per share attributable to common stockholders is computed by dividing net (loss) income attributable to common stockholders by the weighted-average number of common equivalent shares outstanding for the period. Diluted net (loss) income per share attributable to common stockholders includes any dilutive effect from outstanding stock options and warrants using the treasury stock method.
	The following common stock issuable upon the conversion or exercise of dilutive securities has been excluded from the diluted net (loss) income per share attributable to common stockholders calculation because their effect would have been antidilutive for the periods presented:
	(Shares in thousands)		YEARS ENDED
			DECEMBER 31,
			2013			2012			2011
	Convertible preferred stock			7,209			9,824			—
	Options to purchase common stock			2,338			2,347			551
	Warrants to purchase convertible preferred stock			61			87			88
	Warrants to purchase common stock			1			—			—
				9,609			12,258			639
			YEARS ENDED DECEMBER 31,
	(in thousands, except per share data)		2013			2012			2011
	Basic
	Numerator:
	Net (loss) income		$	(28,872	)	$	(27,595	)	$	19,710
	Net income attributable to participating securities			—			—			(18,823	)
	Net (loss) income attributable to common stockholders for basic net (loss) income per share		$	(28,872	)	$	(27,595	)	$	887
	Denominator:
	Weighted-average common shares outstanding			5,523			1,197			1,152
	Basic net (loss) income per common share		$	(5.23	)	$	(23.05	)	$	0.77
	Diluted
	Numerator:
	Net (loss) income attributable to common stockholders for basic net (loss) income per share		$	(28,872	)	$	(27,595	)	$	887
	Reallocation of net income attributable to participating securities			—			—			483
	Net (loss) income attributable to common stockholders for diluted net (loss) income per share		$	(28,872	)	$	(27,595	)	$	1,370
	Denominator:
	Weighted-average number of common shares outstanding used in computing basic net (loss) income per common share			5,523			1,197			1,152
	Dilutive effect of:
	Stock options			—			—			752
	Weighted-average number of common shares outstanding used in computing diluted net (loss) income per common share			5,523			1,197			1,904
	Diluted net (loss) income per common share		$	(5.23	)	$	(23.05	)	$	0.72

Organization_and_Summary_of_Si2

Organization and Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
Summary of Assets and Liabilities Recorded at Fair Value	'
	The following table summarizes, for assets and the liability recorded at fair value, the respective fair value and the classification by level of input within the fair value hierarchy defined above (in thousands):
		DECEMBER 31, 2013
					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		$	—
		DECEMBER 31, 2012
					BASIS OF FAIR VALUE MEASUREMENTS
		TOTAL			LEVEL 1			LEVEL 2			LEVEL 3
	Assets
	Money market funds	$	6,910		$	6,910		$	—		$	—
	U.S. Treasury securities		3,577			3,577			—			—
	U.S. government agency securities		23,047			—			23,047			—
	Total cash equivalents and marketable securities	$	33,534		$	10,487		$	23,047		$	—
	Liability
	Preferred stock warrant liability	$	563		$	—		$	—		$	563
Change in Estimated Fair Value of Preferred Stock Warrant Liability	'
	The change in the estimated fair value of the preferred stock warrant liability is summarized below (in thousands):
		YEARS ENDED DECEMBER 31
		2013			2012			2011
	Balance, beginning of year	$	563		$	682		$	622
	Change in fair value recorded in other income (expense), net		(500	)		(119	)		60
	Exercises		(57	)		—			—
	Conversion of preferred stock warrant to common stock warrant and reclassification to permanent equity		(6	)		—			—
	Balance, end of year	$	—		$	563		$	682
Fair Value of Warrants Assumptions	'
	The fair value of the above warrants was determined using the Black-Scholes valuation model with the following assumptions:
		DECEMBER 31
		2012			2011
	Risk-free interest rate		0.2%—0.3%			0.1%—0.4%
	Remaining contractual term (years)		2.1			3
	Volatility		85.00%			85.00%
Securities Excluded from Calculation of Diluted Net (Loss) Income Per share	'
	The following common stock issuable upon the conversion or exercise of dilutive securities has been excluded from the diluted net (loss) income per share attributable to common stockholders calculation because their effect would have been antidilutive for the periods presented:
	(Shares in thousands)	YEARS ENDED
		DECEMBER 31,
		2013			2012			2011
	Convertible preferred stock		7,209			9,824			—
	Options to purchase common stock		2,338			2,347			551
	Warrants to purchase convertible preferred stock		61			87			88
	Warrants to purchase common stock		1			—			—
			9,609			12,258			639
Schedule of Basic and Diluted (Loss) Income Per Share	'
		YEARS ENDED DECEMBER 31,
	(in thousands, except per share data)	2013			2012			2011
	Basic
	Numerator:
	Net (loss) income	$	(28,872	)	$	(27,595	)	$	19,710
	Net income attributable to participating securities		—			—			(18,823	)
	Net (loss) income attributable to common stockholders for basic net (loss) income per share	$	(28,872	)	$	(27,595	)	$	887
	Denominator:
	Weighted-average common shares outstanding		5,523			1,197			1,152
	Basic net (loss) income per common share	$	(5.23	)	$	(23.05	)	$	0.77
	Diluted
	Numerator:
	Net (loss) income attributable to common stockholders for basic net (loss) income per share	$	(28,872	)	$	(27,595	)	$	887
	Reallocation of net income attributable to participating securities		—			—			483
	Net (loss) income attributable to common stockholders for diluted net (loss) income per share	$	(28,872	)	$	(27,595	)	$	1,370
	Denominator:
	Weighted-average number of common shares outstanding used in computing basic net (loss) income per common share		5,523			1,197			1,152
	Dilutive effect of:
	Stock options		—			—			752
	Weighted-average number of common shares outstanding used in computing diluted net (loss) income per common share		5,523			1,197			1,904
	Diluted net (loss) income per common share	$	(5.23	)	$	(23.05	)	$	0.72

Cash_Equivalents_and_Marketabl1

Cash Equivalents and Marketable Securities (Tables)	12 Months Ended
	Dec. 31, 2013
Cash And Cash Equivalents [Abstract]	'
Summary of Cash Equivalents and Marketable Securities	'
	The following is a summary of our cash equivalents and marketable securities at December 31, 2013 and 2012:
	(in thousands)	DECEMBER 31, 2013
		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
	(in thousands)	DECEMBER 31, 2012
		AMORTIZED			UNREALIZED		UNREALIZED			ESTIMATED
		COST BASIS			GAINS		LOSSES			FAIR VALUE
	Money market funds	$	6,910		$	—	$	—		$	6,910
	U.S. Treasury securities		3,576			1		—			3,577
	U.S. government agency securities		23,041			6		—			23,047
			33,527			7		—			33,534
	Less: cash equivalents		(6,910	)		—		—			(6,910	)
	Total marketable securities	$	26,617		$	7	$	—		$	26,624
Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale Securities by Contractual Maturity	'
	As of December 31, 2013, 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
	Debt securities maturing:
	In one year or less	$	66,459		$	66,461
	In one to two years		7,554			7,556
	Total marketable securities	$	74,013		$	74,017

Property_and_Equipment_Tables

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2013
Property Plant And Equipment [Abstract]	'
Components of Property and Equipment	'
	Property and equipment consist of the following:
	(in thousands)	DECEMBER 31
		2013			2012
	Computer equipment and software	$	1,097		$	1,145
	Furniture and fixtures		694			690
	Laboratory equipment		9,596			9,112
	Leasehold improvements		2,173			2,135
			13,560			13,082
	Less: accumulated depreciation and amortization		(9,816	)		(8,451	)
	Property and equipment, net	$	3,744		$	4,631

Commitments_Tables

Commitments (Tables)	12 Months Ended
	Dec. 31, 2013
Commitments And Contingencies Disclosure [Abstract]	'
Schedule of Estimated Future Minimum Commitments for Operating Leases	'
	The estimated future minimum commitments under these noncancelable operating leases are as follows:
	(in thousands)
	Year ending December 31:
	2014		2,710
	2015		2,794
	2016		2,877
	2017		2,960
	Total estimated minimum payments	$	11,341

Stockholders_Equity_Deficit_Ta

Stockholders' Equity (Deficit) (Tables)	12 Months Ended
	Dec. 31, 2013
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
		NUMBER			WEIGHTED-
		OF SHARES			AVERAGE
					EXERCISE PRICE
					PER SHARE
	Balance at December 31, 2010		1,996,513		$	4.06
	Options granted		448,443		$	8.36
	Options exercised		(26,152	)	$	1.48
	Options forfeited		(206,157	)	$	5.04
	Options expired		(21,264	)	$	3.57
	Balance at December 31, 2011		2,191,383		$	4.92
	Options granted		526,134		$	5.78
	Options exercised		(64,208	)	$	1.6
	Options forfeited		(32,611	)	$	6.89
	Options expired		(75,467	)	$	3.2
	Balance at December 31, 2012		2,545,231		$	5.17
	Options granted		584,529		$	7.08
	Options exercised		(168,359	)	$	3.07
	Options forfeited		(53,246	)	$	6.87
	Options expired		(671,158	)	$	4.12
	Balance at December 31, 2013		2,236,997		$	6.09
	Options exercisable		1,287,357		$	5.48
Schedule of Stock-Based Compensation Expenses Recognized	'
	Total stock-based compensation expense recognized was as follows:
	(in thousands)	YEARS ENDED DECEMBER 31
		2013			2012			2011
	Research and development	$	968		$	705		$	668
	General and administrative		1,178			1,016			2,259
	Total	$	2,146		$	1,721		$	2,927
Schedule of Stock Option Weighted-Average Assumptions	'
	The fair value of each stock option was estimated using the Black-Scholes option-pricing model based on the date of grant of such stock option with the following assumptions:
		Options									ESPP
		Year Ended December 31,									Year Ended December 31,
		2013			2012			2011			2013			2012		2011
	Expected term (years)		5.0-6.1			5.0-6.1			5.3-6.1			0.5			—		—
	Expected volatility		85	%		85	%		85	%		62	%		—		—
	Risk-free interest rate		0.8-2.0	%		0.6-1.1	%		1.3-2.6	%		0.1	%		—		—
	Expected dividend yield		0	%		0	%		0	%		0	%		—		—

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2013
Income Tax Disclosure [Abstract]	'
Schedule of Reconciliation of Federal Statutory Income Tax Rate	'
	A reconciliation of the federal statutory income tax rate to our effective income tax rate is as follows:
	(in thousands)	YEARS ENDED DECEMBER 31,
		2013			2012			2011
	Federal statutory income tax rate	$	(10,105	)	$	(9,658	)	$	6,899
	Nondeductible stock compensation		455			386			414
	Nontaxable equity premiums		(532	)		(452	)		(825	)
	Deferred tax assets (utilized) not benefitted		10,338			9,750			(6,527	)
	Other permanent items		(156	)		(26	)		39
	(Benefit) from income taxes	$	—		$	—		$	—
Schedule of Deferred Tax Assets and Liabilities	'
	The tax effects of temporary differences and carryforwards that give rise to significant portions of the deferred tax assets consist of the following (in thousands):
		YEARS ENDED DECEMBER 31,
		2013			2012			2011
	Net operating loss carryforwards	$	59,552		$	48,613		$	37,905
	Research and development credit		6,564			5,372			5,218
	Reserves and accruals		5,936			6,020			5,204
	Total deferred tax assets		72,052			60,005			48,327
	Deferred tax liability		—			—			—
	Net deferred tax asset		72,052			60,005			48,327
	Less: valuation allowance		(72,052	)		(60,005	)		(48,327	)
	Net deferred tax assets	$	—		$	—		$	—
Schedule of Reconciliation of Unrecognized Tax Benefits	'
	A reconciliation of our unrecognized tax benefits for the years ended December 31, 2013, 2012 and 2011, is as follows:
	(in thousands)	UNRECOGNIZED
		INCOME TAX
		BENEFITS
	Balance as of January 1, 2011	$	1,313
	Additions for current year tax positions		144
	Balance as of December 31, 2011		1,457
	Additions for current year tax positions		78
	Balance as of December 31, 2012		1,535
	Deductions for prior year tax positions		27
	Additions for current year tax positions		219
	Balance as of December 31, 2013	$	1,781

Selected_Quarterly_Financial_I1

Selected Quarterly Financial Information (Tables)	12 Months Ended
	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]	'
Summary of Quarterly Financial Information	'
	The following amounts are in thousands, except per share amounts:
		Quarter Ended
	Quarterly Results of Operations	March 31,			June 30,			September 30,			December 31,
		2013			2013			2013			2013
		(Unaudited)
		(In thousands, except per share amounts)
	Revenue	$	2,975		$	3,549		$	3,482		$	3,785
	Net loss		(7,047	)		(7,274	)		(7,234	)		(7,317	)
	Basic and diluted net loss per share		(5.73	)		(5.82	)		(2.74	)		(0.43	)
		Quarter Ended
	Quarterly Results of Operations	March 31,			June 30,			September 30,			December 31,
		2012			2012			2012			2012
		(Unaudited)
		(In thousands, except per share amounts)
	Revenue	$	2,014		$	2,183		$	2,862		$	2,924
	Net loss		(8,081	)		(6,843	)		(5,858	)		(6,813	)
	Basic and diluted net loss per share		(6.92	)		(5.72	)		(4.85	)		(5.59	)

Organization_and_Summary_of_Si3

Organization and Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)

0 Months Ended

1 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

Sep. 04, 2013

Sep. 30, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Sep. 30, 2013

Feb. 28, 2005

Jun. 30, 2004

Dec. 31, 2002

Jan. 26, 2014

Dec. 31, 2013

Dec. 31, 2013

Segment

Employees and directors [Member]

Employees and directors [Member]

Employees and directors [Member]

Non employee options [Member]

Non employee options [Member]

Non employee options [Member]

Series A convertible preferred stock [Member]

Series A convertible preferred stock [Member]

Series A convertible preferred stock [Member]

Series A convertible preferred stock [Member]

Subsequent Event [Member]

Minimum [Member]

Maximum [Member]

Business And Summary Of Significant Accounting Policies [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of operating segments

'

'

1

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of common stock issued through IPO

'

5,520,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net proceeds after underwriting discounts, commissions and offering expenses

'

$63,800,000

$63,849,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Reverse stock split

'1-for-12.3

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Short-term restricted cash

'

'

'

'

38,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Net number of warrants exercised

'

4,376

'

'

'

'

'

'

'

'

'

'

'

'

'

768

'

'

Gain (Loss) related the change in fair value of other income

'

83,000

'

'

'

'

'

'

'

'

'

-3,000

'

'

'

'

'

'

Reclassification of warrant liability to permanent equity

'

57,000

57,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Fair value price of warrants, per share

'

$13

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Outstanding warrant converted into a warrant to purchase, number of shares

'

2,304

'

'

'

'

'

'

'

'

'

2,304

81,300

2,304

3,902

'

'

'

Outstanding warrant converted into a warrant to purchase, per share

'

12.3

'

'

'

'

'

'

'

'

'

12.3

12.3

12.3

12.3

'

'

'

Reclassification of warrant liability to equity

'

6,000

6,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Property and equipment estimated useful lives

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'3 years

'5 years

Stock-based compensation expense

'

'

$2,146,000

$1,721,000

$2,927,000

$2,067,000

$1,655,000

$2,850,000

$79,000

$66,000

$77,000

'

'

'

'

'

'

'

Organization_and_Summary_of_Si4

Organization and Summary of Significant Accounting Policies - Summary of Assets and Liabilities Recorded at Fair Value (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Preferred stock warrant liability [Member]	'	'
Liability	'	'
Liability	'	$563
Money market funds [Member]	'	'
Assets	'	'
Assets	6,456	6,910
U.S. Treasury securities [Member]	'	'
Assets	'	'
Assets	18,852	3,577
U.S. government agency securities [Member]	'	'
Assets	'	'
Assets	48,709	23,047
Total cash equivalents and marketable securities [Member]	'	'
Assets	'	'
Assets	74,017	33,534
Level 1 [Member] | Preferred stock warrant liability [Member]	'	'
Liability	'	'
Liability	'	'
Level 1 [Member] | Money market funds [Member]	'	'
Assets	'	'
Assets	6,456	6,910
Level 1 [Member] | U.S. Treasury securities [Member]	'	'
Assets	'	'
Assets	18,852	3,577
Level 1 [Member] | U.S. government agency securities [Member]	'	'
Assets	'	'
Assets	'	'
Level 1 [Member] | Total cash equivalents and marketable securities [Member]	'	'
Assets	'	'
Assets	25,308	10,487
Level 2 [Member] | Preferred stock warrant liability [Member]	'	'
Liability	'	'
Liability	'	'
Level 2 [Member] | Money market funds [Member]	'	'
Assets	'	'
Assets	'	'
Level 2 [Member] | U.S. Treasury securities [Member]	'	'
Assets	'	'
Assets	'	'
Level 2 [Member] | U.S. government agency securities [Member]	'	'
Assets	'	'
Assets	48,709	23,047
Level 2 [Member] | Total cash equivalents and marketable securities [Member]	'	'
Assets	'	'
Assets	48,709	23,047
Level 3 [Member] | Preferred stock warrant liability [Member]	'	'
Liability	'	'
Liability	'	563
Level 3 [Member] | Money market funds [Member]	'	'
Assets	'	'
Assets	'	'
Level 3 [Member] | U.S. Treasury securities [Member]	'	'
Assets	'	'
Assets	'	'
Level 3 [Member] | U.S. government agency securities [Member]	'	'
Assets	'	'
Assets	'	'
Level 3 [Member] | Total cash equivalents and marketable securities [Member]	'	'
Assets	'	'
Assets	'	'

Organization_and_Summary_of_Si5

Organization and Summary of Significant Accounting Policies - Change in Estimated Fair Value of Preferred Stock Warrant Liability (Detail) (USD $)	1 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Fair Value Disclosures [Abstract]	'	'	'	'
Balance, beginning of year	'	$563	$682	$622
Change in fair value recorded in other income (expense), net	'	-500	-119	60
Exercises	-57	-57	'	'
Conversion of preferred stock warrant to common stock warrant and reclassification to permanent equity	-6	-6	'	'
Balance, end of year	'	'	$563	$682

Organization_and_Summary_of_Si6

Organization and Summary of Significant Accounting Policies - Fair Value of Warrants Assumptions (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]	'	'
Remaining contractual term (years)	'2 years 1 month 6 days	'3 years
Volatility	85.00%	85.00%
Minimum [Member]	'	'
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]	'	'
Risk-free interest rate	0.20%	0.10%
Maximum [Member]	'	'
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]	'	'
Risk-free interest rate	0.30%	0.40%

Organization_and_Summary_of_Si7

Organization and Summary of Significant Accounting Policies - Securities Excluded from Calculation of Diluted Net (Loss) Income Per Share (Detail)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Dilutive Securities Included And Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'
Securities excluded from calculation of diluted net (loss) income per share	9,609	12,258	639
Convertible preferred stock [Member]	'	'	'
Dilutive Securities Included And Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'
Securities excluded from calculation of diluted net (loss) income per share	7,209	9,824	'
Options to purchase common stock [Member]	'	'	'
Dilutive Securities Included And Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'
Securities excluded from calculation of diluted net (loss) income per share	2,338	2,347	551
Warrants to purchase convertible preferred stock [Member]	'	'	'
Dilutive Securities Included And Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'
Securities excluded from calculation of diluted net (loss) income per share	61	87	88
Warrants to purchase common stock [Member]	'	'	'
Dilutive Securities Included And Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'
Securities excluded from calculation of diluted net (loss) income per share	1	'	'

Organization_and_Summary_of_Si8

Organization and Summary of Significant Accounting Policies - Schedule of Basic and Diluted (Loss) Income Per Share (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Numerator:	'	'	'	'	'	'	'	'	'	'	'
Net (loss) income	'	'	'	'	'	'	'	'	($28,872)	($27,595)	$19,710
Net income attributable to participating securities	'	'	'	'	'	'	'	'	'	'	-18,823
Net (loss) income attributable to common stockholders for basic net (loss) income per share	-7,317	-7,234	-7,274	-7,047	-6,813	-5,858	-6,843	-8,081	-28,872	-27,595	887
Denominator:	'	'	'	'	'	'	'	'	'	'	'
Weighted-average common shares outstanding, basic	'	'	'	'	'	'	'	'	5,523	1,197	1,152
Basic net (loss) income per common share	'	'	'	'	'	'	'	'	($5.23)	($23.05)	$0.77
Numerator:	'	'	'	'	'	'	'	'	'	'	'
Net (loss) income attributable to common stockholders for basic net (loss) income per share	'	'	'	'	'	'	'	'	-28,872	-27,595	887
Reallocation of net income attributable to participating securities	'	'	'	'	'	'	'	'	'	'	483
Net (loss) income attributable to common stockholders for diluted net (loss) income per share	'	'	'	'	'	'	'	'	($28,872)	($27,595)	$1,370
Denominator:	'	'	'	'	'	'	'	'	'	'	'
Weighted-average common shares outstanding, basic	'	'	'	'	'	'	'	'	5,523	1,197	1,152
Dilutive effect of:	'	'	'	'	'	'	'	'	'	'	'
Stock options	'	'	'	'	'	'	'	'	'	'	752
Weighted-average number of common shares outstanding used in computing diluted net (loss) income per common share	'	'	'	'	'	'	'	'	5,523	1,197	1,904
Diluted net (loss) income per common share	'	'	'	'	'	'	'	'	($5.23)	($23.05)	$0.72

Cash_Equivalents_and_Marketabl2

Cash Equivalents and Marketable Securities - Summary of Cash Equivalents and Marketable Securities (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]	'	'
AMORTIZED COST BASIS	$67,557	$26,617
UNREALIZED GAINS	7	7
UNREALIZED LOSSES	-3	'
ESTIMATED FAIR VALUE	67,561	26,624
Money market funds [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
AMORTIZED COST BASIS	6,456	6,910
UNREALIZED GAINS	'	'
UNREALIZED LOSSES	'	'
ESTIMATED FAIR VALUE	6,456	6,910
U.S. Treasury securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
AMORTIZED COST BASIS	18,848	3,576
UNREALIZED GAINS	4	1
UNREALIZED LOSSES	'	'
ESTIMATED FAIR VALUE	18,852	3,577
U.S. government agency securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
AMORTIZED COST BASIS	48,709	23,041
UNREALIZED GAINS	3	6
UNREALIZED LOSSES	-3	'
ESTIMATED FAIR VALUE	48,709	23,047
Marketable securities including cash equivalents [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
AMORTIZED COST BASIS	74,013	33,527
UNREALIZED GAINS	7	7
UNREALIZED LOSSES	-3	'
ESTIMATED FAIR VALUE	74,017	33,534
Cash equivalents [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
AMORTIZED COST BASIS	-6,456	-6,910
UNREALIZED GAINS	'	'
UNREALIZED LOSSES	'	'
ESTIMATED FAIR VALUE	($6,456)	($6,910)

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 $)	Dec. 31, 2013
In Thousands, unless otherwise specified
Debt securities maturing:	'
Amortized Cost, In one year or less	$66,459
Amortized Cost, In one to two years	7,554
Total marketable securities, Amortized Cost	74,013
Estimated Fair Value, In one year or less	66,461
Estimated Fair Value, In one to two years	7,556
Total marketable securities, Estimated Fair Value	$74,017

Cash_Equivalents_and_Marketabl4

Cash Equivalents and Marketable Securities - Additional Information (Detail) (Marketable securities [Member], USD $)	12 Months Ended
	Dec. 31, 2013
Marketable securities [Member]	'
Schedule of Available-for-sale Securities [Line Items]	'
Gross unrealized losses on marketable securities	$3,000
Sales of available-for-sale securities	$0

Property_and_Equipment_Compone

Property and Equipment - Components of Property and Equipment (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Property, Plant and Equipment [Line Items]	'	'
Property and equipment, gross	$13,560	$13,082
Less: accumulated depreciation and amortization	-9,816	-8,451
Property and equipment, net	3,744	4,631
Computer equipment and software [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment, gross	1,097	1,145
Furniture and fixtures [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment, gross	694	690
Laboratory equipment [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment, gross	9,596	9,112
Leasehold improvements [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment, gross	$2,173	$2,135

Preferred_Stock_and_Common_Sto1

Preferred Stock and Common Stock Warrant - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended					1 Months Ended
	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2007	Jan. 26, 2014	Dec. 31, 2007	Dec. 31, 2007	Sep. 30, 2013	Dec. 31, 2002	Feb. 28, 2005	Jun. 30, 2004
			Warrant	Subsequent Event [Member]	Warrants one [Member]	Warrants two [Member]	Series A convertible preferred stock [Member]	Series A convertible preferred stock [Member]	Series A convertible preferred stock [Member]	Series A convertible preferred stock [Member]
Class of Warrant or Right [Line Items]	'	'	'	'	'	'	'	'	'	'
Warrant to purchase preferred stock, number of shares	2,304	'	'	'	44,715	36,585	2,304	3,902	81,300	2,304
Warrant to purchase preferred stock, per share	12.3	'	'	'	'	'	12.3	12.3	12.3	12.3
Warrant to purchase preferred stock, expiration	'	'	'	'	'	'	'	'December 2012	'	'
Gain (Loss) related the change in fair value of other income	$83,000	'	'	'	'	'	($3,000)	'	'	'
Reclassification of warrant liability to equity	6,000	6,000	'	'	'	'	'	'	'	'
Net number of warrants exercised	4,376	'	'	768	'	'	'	'	'	'
Number of warrants	'	'	2	'	'	'	'	'	'	'
Reclassification of warrant liability to permanent equity	$57,000	$57,000	'	'	'	'	'	'	'	'
Fair value price of warrants, per share	$13	'	'	'	'	'	'	'	'	'

Commitments_Additional_Informa

Commitments - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Leases Operating [Abstract]	'	'	'
Lease option additional extend term	'3 years	'	'
Lease expiration	31-Dec-17	'	'
Deferred rent	$2,146,000	$2,448,000	'
Incentive to lessee	1,700,000	'	'
Unamortized leasehold improvement incentive total	900,000	1,100,000	'
Unamortized leasehold improvement incentive included in other long-term liabilities	700,000	900,000	'
Rent expense	$1,900,000	$1,900,000	$1,900,000

Commitments_Schedule_of_Estima

Commitments - Schedule of Estimated Future Minimum Commitments (Detail) (USD $)	Dec. 31, 2013
In Thousands, unless otherwise specified
Leases Operating [Abstract]	'
2014	$2,710
2015	2,794
2016	2,877
2017	2,960
Total estimated minimum payments	$11,341

Convertible_Preferred_Stock_Ad

Convertible Preferred Stock - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2013
Temporary Equity Disclosure [Abstract]	'
Preferred stock converted into common stock	9,929,159

Stockholders_Equity_Deficit_Ad

Stockholders' Equity (Deficit) - Additional Information (Detail) (USD $)

0 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

12 Months Ended

Sep. 23, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Feb. 28, 2013

Aug. 31, 2011

Mar. 31, 2011

Dec. 31, 2013

Feb. 28, 2013

Aug. 31, 2011

Feb. 28, 2013

Aug. 31, 2011

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Incremental stock-based compensation expenses [Member]

Incremental stock-based compensation expenses [Member]

Incremental stock-based compensation expenses [Member]

Incremental stock-based compensation expenses [Member]

Incremental stock-based compensation expenses [Member]

Incremental stock-based compensation expenses [Member]

Incremental stock-based compensation expenses [Member]

Incremental stock-based compensation expenses [Member]

2013 Omnibus Incentive Plan [Member]

Prior Plans [Member]

2013 Employee Stock Purchase Plan [Member]

2013 Employee Stock Purchase Plan [Member]

Employees

Minimum [Member]

Minimum [Member]

Maximum [Member]

Maximum [Member]

Restricted Stock Awards [Member]

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

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Additional awards granted

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Common stock available for issuance

'

'

'

'

'

'

'

'

'

'

'

'

3,500,000

1,069,985

'

'

Percent of annual increase in common stock available for issuance

'

'

'

'

'

'

'

'

'

'

'

'

4.00%

'

1.00%

'

Nonstatutory stock options granted, exercise price percentage

'

85.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Stock options granted to a stockholder owning more than 10%, exercise price percentage

'

110.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Stock options granted, expiration term

'

'10 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Options vesting period

'

'4 years

'

'

'

'

'

'

'18 months

'3 months

'20 months

'18 months

'

'

'

'

Number of shares of common stock reserved for future issuance

'

'

'

'

'

'

'

'

'

'

'

'

'

'

250,000

'

Maximum increase in shares reserved for issuance

'

'

'

'

'

'

'

'

'

'

'

'

'

'

300,000

'

Common stock available for issuance, description

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'Unless our Board provides otherwise, beginning on January 1, 2014, and continuing until the expiration of the ESPP, the total number of shares of common stock available for issuance under the ESPP will automatically increase annually on January 1 by the lesser of (i) 1% of the total number of issued and outstanding shares of common stock as of December 31 of the immediately preceding year, or (ii) 300,000 shares of common stock.

'

Shares available for future issuance

'

'

'

'

'

'

'

'

'

'

'

'

3,466,450

'

'

'

Number of options vested

'

2,182,957

'

'

'

'

80,649

'

'

'

'

'

'

'

'

'

Stock options to purchase common stock outstanding, weighted-average exercise price

'

$6.07

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Options outstanding, weighted-average remaining contractual term

'

'7 years 3 months 18 days

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Weighted-average remaining contractual term options exercisable

'

'6 years 3 months 18 days

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Aggregate intrinsic value of options outstanding

'

$23,900,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Aggregate intrinsic value of options exercisable

'

14,600,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Closing price of common stock

'

$16.79

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Aggregate intrinsic value of options expected to vest

'

23.4

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Award issued under restricted shares of common stock

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,000

Grand date fair value

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$15.64

Restricted stock award expiry date

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

31-Mar-14

Purchase price per share as a percentage of fair market value of our common stock

'

'

'

'

'

'

'

'

'

'

'

'

'

'

85.00%

'

Shares issued under ESPP

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0

'

Stock-based compensation expense

'

2,146,000

1,721,000

2,927,000

'

500,000

'

'

'

'

'

'

'

'

42,000

'

Total unrecognized compensation expense

'

4,300,000

'

'

'

'

'

'

'

'

'

'

'

'

100,000

'

Unrecognized compensation expense expected to recognize, weighted-average period

'

'2 years 8 months 12 days

'

'

'

'

'

'

'

'

'

'

'

'

'4 months 15 days

'

Number of options to which vesting conditions amended

'

'

'

'

'

'

2

'

'

'

'

'

'

'

'

'

Number of employees effected

'

'

'

'

'

'

2

'

'

'

'

'

'

'

'

'

Agreement term

'

'

'

'

'

'

'12 months

'

'

'

'

'

'

'

'

'

Upfront payment

'

'

'

'

'

'

50,000,000

'

'

'

'

'

'

'

'

'

Performance-based options, amendment description

'

'

'

'

'

'

'The original terms of the performance-based options provided that the options to two employees would partially vest in the event we enter into a definitive agreement for a strategic alliance or partnership with an upfront payment over $50 million. As amended, the terms of the performance-based options provide that the options would partially vest in the event we enter into one or more definitive agreements for strategic alliances or partnerships within a 12-month period with aggregate upfront payments over $50 million.

'

'

'

'

'

'

'

'

'

Incremental stock-based compensation expense

'

'

'

'

157,000

500,000

'

600,000

'

'

'

'

'

'

'

'

Acceleration of nonvested options held by former CEO upon separation

'

'

'

'

'

50.00%

'

'

'

'

'

'

'

'

'

'

Expected dividend yield

'

0.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Weighted-average grant-date fair value per share of stock options granted

'

$5.05

$4.06

$6.03

'

'

'

'

'

'

'

'

'

'

'

'

Total intrinsic value of options exercised

'

$1,100,000

$300,000

$200,000

'

'

'

'

'

'

'

'

'

'

'

'

Stockholders_Equity_Deficit_Sc

Stockholders' Equity (Deficit) - Schedule of Option Activity under Stock Plans and Related Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'	'	'
NUMBER OF SHARES, Beginning balance	2,545,231	2,191,383	1,996,513
NUMBER OF SHARES, Options granted	584,529	526,134	448,443
NUMBER OF SHARES, Options exercised	-168,359	-64,208	-26,152
NUMBER OF SHARES, Options forfeited	-53,246	-32,611	-206,157
NUMBER OF SHARES, Options expired	-671,158	-75,467	-21,264
NUMBER OF SHARES, Ending balance	2,236,997	2,545,231	2,191,383
NUMBER OF SHARES, Options exercisable	1,287,357	'	'
WEIGHTED-AVERAGE EXERCISE PRICE PER SHARE, Options beginning balance	$5.17	$4.92	$4.06
WEIGHTED-AVERAGE EXERCISE PRICE PER SHARE, Options granted	$7.08	$5.78	$8.36
WEIGHTED-AVERAGE EXERCISE PRICE PER SHARE, Options exercised	$3.07	$1.60	$1.48
WEIGHTED-AVERAGE EXERCISE PRICE PER SHARE, Options forfeited	$6.87	$6.89	$5.04
WEIGHTED-AVERAGE EXERCISE PRICE PER SHARE, Options expired	$4.12	$3.20	$3.57
WEIGHTED-AVERAGE EXERCISE PRICE PER SHARE, Options ending balance	$6.09	$5.17	$4.92
WEIGHTED-AVERAGE EXERCISE PRICE PER SHARE, Options exercisable	$5.48	'	'

Stockholders_Equity_Deficit_Sc1

Stockholders' Equity (Deficit) - Schedule of Stock-Based Compensation Expenses Recognized (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'	'
Stock-based compensation expense recognized	$2,146	$1,721	$2,927
Research and development [Member]	'	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'	'
Stock-based compensation expense recognized	968	705	668
General and administrative [Member]	'	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'	'
Stock-based compensation expense recognized	$1,178	$1,016	$2,259

Stockholders_Equity_Deficit_Sc2

Stockholders' Equity (Deficit) - Schedule of Stock Option Weighted-Average Assumptions (Detail)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Expected dividend yield	0.00%	'	'
Options [Member]	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Expected volatility	85.00%	85.00%	85.00%
Expected dividend yield	0.00%	0.00%	0.00%
Options [Member] | Minimum [Member]	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Expected term (years)	'5 years	'5 years	'5 years 3 months 18 days
Risk-free interest rate	0.80%	0.60%	1.30%
Options [Member] | Maximum [Member]	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Expected term (years)	'6 years 1 month 6 days	'6 years 1 month 6 days	'6 years 1 month 6 days
Risk-free interest rate	2.00%	1.10%	2.60%
ESPP [Member]	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Expected term (years)	'6 months	'	'
Expected volatility	'	'	'
Risk-free interest rate	0.10%	'	'
Expected dividend yield	0.00%	'	'

Employee_Benefit_Plans_Additio

Employee Benefit Plans - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2013
Compensation And Retirement Disclosure [Abstract]	'
Eligible employees contribution percentage	100.00%

Collaborative_Research_and_Dev1

Collaborative Research and Development Agreements - Additional Information (Detail) (USD $)

1 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

1 Months Ended

0 Months Ended

12 Months Ended

Mar. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Aug. 31, 2008

31-May-08

Dec. 31, 2011

31-May-08

31-May-08

31-May-08

Jun. 30, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

31-May-10

Dec. 31, 2013

Dec. 31, 2013

Series A-2 convertible preferred stock [Member]

Series A-2 convertible preferred stock [Member]

Pfizer Inc. [Member]

Pfizer Inc. [Member]

Pfizer Inc. [Member]

Pfizer Inc. [Member]

Pfizer Inc. [Member]

Pfizer Inc. [Member]

Fast Forward LLC [Member]

Fast Forward LLC [Member]

Fast Forward LLC [Member]

Fast Forward LLC [Member]

Fast Forward LLC [Member]

Fast Forward LLC [Member]

Fast Forward LLC [Member]

Series A-2 convertible preferred stock [Member]

Upfront technology [Member]

Milestone payment [Member]

Milestone payment [Member]

Royalties [Member]

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Upfront payment

$6,000,000

'

'

'

'

'

$7,500,000

'

'

'

'

'

'

'

'

'

'

'

Milestone payment received

'

'

'

'

'

7,500,000

'

'

'

'

'

'

'

'

'

'

'

'

Research funding received

'

'

'

'

'

'

'

3,800,000

'

'

'

'

'

'

'

'

'

'

Deferred revenue recognition research period

'5 years

'

'

'

'

'

'

'

'

'3 years

'3 years

'

'

'

'

'

'

'

Convertible preferred stock issued

'

0

0

0

2,099,842

'

'

'

1,538,123

'

'

'

'

'

'

'

'

'

Convertible preferred stock price per share

'

'

'

'

'

'

'

'

$22.76

'

'

'

'

'

'

'

'

'

Proceeds from issuance of preferred stock

'

'

6,819,000

'

'

'

'

'

35,000,000

'

'

'

'

'

'

'

'

'

Recognized revenue under collaboration arrangement

'

2,200,000

'

'

'

'

'

7,200,000

10,900,000

'

'

'

100,000

100,000

100,000

'

'

'

Revenue recognition research period

'

'

'

'

'

'

'

'

'3 years

'

'

'

'

'

'

'

'

'

Total research funding

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,000,000

'

'

Research agreement amount received

2,200,000

'

'

'

'

'

'

'

'

'

'

600,000

'

'

'

'

'

'

Deferred revenue recognized under collaboration arrangement

'

'

'

'

'

'

'

'

'

'

'

'

100,000

300,000

'

'

'

'

Collaboration arrangement, contingent payments

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$200,000

$2,800,000

Collaborative_Research_and_Dev2

Collaborative Research and Development Agreements - Additional Information 1 (Detail) (USD $)

1 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

12 Months Ended

Mar. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Oct. 31, 2013

Sep. 30, 2013

Aug. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

31-May-11

Dec. 31, 2013

Apr. 30, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Series A-2 convertible preferred stock [Member]

Series A-2 convertible preferred stock [Member]

Series A-3 convertible preferred stock [Member]

Series A-3 convertible preferred stock [Member]

Glaxo Smith Kline LLC [Member]

Glaxo Smith Kline LLC [Member]

Glaxo Smith Kline LLC [Member]

Glaxo Smith Kline LLC [Member]

Glaxo Smith Kline LLC [Member]

Glaxo Smith Kline LLC [Member]

Glaxo Smith Kline LLC [Member]

Glaxo Smith Kline LLC [Member]

Glaxo Smith Kline LLC [Member]

Glaxo Smith Kline LLC [Member]

Glaxo Smith Kline LLC [Member]

Glaxo Smith Kline LLC [Member]

Glaxo Smith Kline LLC [Member]

Glaxo Smith Kline LLC [Member]

Glaxo Smith Kline LLC [Member]

Glaxo Smith Kline LLC [Member]

Glaxo Smith Kline LLC [Member]

Glaxo Smith Kline LLC [Member]

Muscle Disorders Discovery Collaboration [Member]

Muscle Disorders Discovery Collaboration [Member]

Muscle Disorders Discovery Collaboration [Member]

Muscle Disorders Discovery Collaboration [Member]

Muscle Disorders Discovery Collaboration [Member]

Muscle Disorders Discovery Collaboration [Member]

Muscle Disorders Discovery Collaboration [Member]

Muscle Disorders Discovery Collaboration [Member]

Respiratory Diseases Discovery Collaboration [Member]

Respiratory Diseases Discovery Collaboration [Member]

Respiratory Diseases Discovery Collaboration [Member]

Respiratory Diseases Discovery Collaboration [Member]

Respiratory Diseases Discovery Collaboration [Member]

Respiratory Diseases Discovery Collaboration [Member]

Respiratory Diseases Discovery Collaboration [Member]

Respiratory Diseases Discovery Collaboration [Member]

Respiratory Diseases Discovery Collaboration [Member]

Respiratory Diseases Discovery Collaboration [Member]

Series A-2 convertible preferred stock [Member]

Phase 1 clinical trial [Member]

Phase 2 clinical trial [Member]

Track 2 Target [Member]

GLP Toxicology Study [Member]

Development costs [Member]

Development costs [Member]

Series A-3 convertible preferred stock [Member]

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Upfront payment

$6,000,000

'

'

'

'

'

'

'

'

$7,000,000

'

'

'

'

'

$7,500,000

'

'

'

'

'

'

'

'

'

Deferred revenue recognition research period

'5 years

'

'

'

'

'

'

'

'

'3 years

'

'

'

'

'

'4 years

'

'

'

'

'

'

'

'

'

Research funding

2,000,000

'

'

'

'

'

'

'

'

'

'

'

'

6,300,000

'

10,500,000

'

'

'

'

'

'

'

'

'

Research funding received

'

'

'

'

'

'

'

'

'

'

1,500,000

4,200,000

3,600,000

'

'

'

3,400,000

1,300,000

'

'

'

'

'

'

'

Preclinical milestone payments

'

'

'

'

'

'

'

'

'

'

1,800,000

'

'

'

'

'

1,800,000

'

'

'

'

'

'

'

'

Convertible preferred stock issued

'

0

0

0

2,099,842

0

381,693

'

'

'

'

'

'

'

329,597

'

'

'

'

'

'

'

'

'

381,693

Convertible preferred stock price per share

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$22.76

'

'

'

'

'

'

'

'

'

$26.20

Proceeds from issuance of preferred stock

'

'

6,819,000

'

'

'

'

'

'

'

'

'

'

'

7,500,000

'

'

'

'

'

'

'

'

'

10,000,000

Deferred revenue recognized under collaboration arrangement

'

'

'

'

'

'

'

'

'

'

1,900,000

5,700,000

'

'

3,000,000

'

6,800,000

8,800,000

'

'

'

'

'

'

3,100,000

Milestone payment received

'

'

'

'

'

'

'

300,000

'

'

'

300,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Extension fee

'

'

'

'

'

'

'

'

200,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Extended evaluation period

'

'

'

'

'

'

'

'

'8 months

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Recognized revenue under collaboration arrangement

'

2,200,000

'

'

'

'

'

'

'

'

5,800,000

5,800,000

5,200,000

'

'

'

5,600,000

3,200,000

'

'

'

'

'

'

'

Potential milestone payments

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

6,500,000

11,000,000

'

4,000,000

'

'

'

Eligible potential milestone payment

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

14,000,000

23,000,000

'

'

'

'

Collaboration receivable

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$100,000

$0

'

Collaborative_Research_and_Dev3

Collaborative Research and Development Agreements - Additional Information 2 (Detail) (USD $)	1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2013	Mar. 31, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013
	Installment		Human Genome Sciences, Inc. [Member]	Human Genome Sciences, Inc. [Member]	Human Genome Sciences, Inc. [Member]	Human Genome Sciences, Inc. [Member]	Human Genome Sciences, Inc. [Member]	Human Genome Sciences, Inc. [Member]	Human Genome Sciences, Inc. [Member]	UCB Pharma S.A. [Member]
							Development costs [Member]	Development costs [Member]	Multiple-Deliverable Revenue Arrangements [Member]	Development costs [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'	'	'	'	'	'	'	'	'	'
Upfront payment	$6	'	$50	'	'	'	'	'	'	'
Recognized revenue under collaboration arrangement	'	2.2	'	0.1	0.9	2.4	'	'	50	'
Collaboration receivable	'	'	'	'	'	'	0	0.1	'	0.2
Collaboration arrangement, contingent payments	'	'	'	435	'	'	'	'	'	'
Expected evaluation period to complete initial research activities	'2 years	'	'	'	'	'	'	'	'	'
Technology access fee received	2.2	'	'	'	'	'	'	'	'	'
Technology access fee	6.6	'	'	'	'	'	'	'	'	'
Contingent technology access fee	4.4	'	'	'	'	'	'	'	'	'
Research funding	2	'	'	'	'	'	'	'	'	'
Number of technology access fee installments	2	'	'	'	'	'	'	'	'	'
Deferred revenue recognition research period	'5 years	'	'	'	'	'	'	'	'	'
Eligible cash receipt for target evaluation and selection	'	0.4	'	'	'	'	'	'	'	'
Deferred revenue relating to collaboration agreement	'	$6.20	'	'	'	'	'	'	'	'

Acquired_Technologies_Addition

Acquired Technologies - Additional Information (Detail) (USD $)	1 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2011
	Installment	Galaxy Biotech, LLC [Member]
		Installment
Research and Development Arrangement, Contract to Perform for Others [Line Items]	'	'
Upfront license payment	'	$3
Number of installments	2	2

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Examination [Line Items]	'	'	'
Income tax expense or benefit	'	'	'
Increase (decrease) in valuation allowance	12,100,000	11,700,000	-7,200,000
Accrued interest or penalties	0	0	'
Incurred interest and penalties	0	'	'
Significant increase(decrease) to uncertain tax positions	0	'	'
Ongoing tax examinations by tax authorities	'We have no ongoing tax examinations by tax authorities at this time.	'	'
Federal tax authority [Member]	'	'	'
Income Tax Examination [Line Items]	'	'	'
Operating loss carryforwards	142,500,000	'	'
Tax credits available to offset future tax	5,400,000	'	'
Operating loss carryforwards, Expiration date	31-Dec-24	'	'
Tax credit carryforwards, Expiration date	31-Dec-23	'	'
State tax authority [Member]	'	'	'
Income Tax Examination [Line Items]	'	'	'
Operating loss carryforwards	168,300,000	'	'
Operating loss carryforwards, Expiration date	31-Dec-15	'	'
Research and development tax credits [Member] | State tax authority [Member]	'	'	'
Income Tax Examination [Line Items]	'	'	'
Tax credits available to offset future tax	$4,000,000	'	'

Income_Taxes_Schedule_of_Recon

Income Taxes - Schedule of Reconciliation of Federal Statutory Income Tax Rate (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]	'	'	'
Federal statutory income tax rate	($10,105)	($9,658)	$6,899
Nondeductible stock compensation	455	386	414
Nontaxable equity premiums	-532	-452	-825
Deferred tax assets (utilized) not benefitted	10,338	9,750	-6,527
Other permanent items	-156	-26	39
(Benefit) from income taxes	'	'	'

Income_Taxes_Schedule_of_Defer

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
Income Tax Disclosure [Abstract]	'	'	'
Net operating loss carryforwards	$59,552	$48,613	$37,905
Research and development credit	6,564	5,372	5,218
Reserves and accruals	5,936	6,020	5,204
Total deferred tax assets	72,052	60,005	48,327
Deferred tax liability	'	'	'
Net deferred tax asset	72,052	60,005	48,327
Less: valuation allowance	-72,052	-60,005	-48,327
Net deferred tax assets	'	'	'

Income_Taxes_Schedule_of_Recon1

Income Taxes - Schedule of Reconciliation of Unrecognized Tax Benefits (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]	'	'	'
Beginning Balance	$1,535	$1,457	$1,313
Deductions for prior year tax positions	27	'	'
Additions for current year tax positions	219	78	144
Ending Balance	$1,781	$1,535	$1,457

Selected_Quarterly_Financial_I2

Selected Quarterly Financial Information - Summary of Quarterly Financial Information (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Statement [Abstract]	'	'	'	'	'	'	'	'	'	'	'
Revenue	$3,785	$3,482	$3,549	$2,975	$2,924	$2,862	$2,183	$2,014	'	'	'
Net loss	($7,317)	($7,234)	($7,274)	($7,047)	($6,813)	($5,858)	($6,843)	($8,081)	($28,872)	($27,595)	$887
Basic and diluted net loss per share	($0.43)	($2.74)	($5.82)	($5.73)	($5.59)	($4.85)	($5.72)	($6.92)	'	'	'

Subsequent_Events_Additional_I

Subsequent Events - Additional Information (Detail) (USD $)	1 Months Ended		12 Months Ended	1 Months Ended	0 Months Ended
	Sep. 30, 2013	Mar. 31, 2013	Dec. 31, 2013	Feb. 28, 2014	Mar. 14, 2014
				Subsequent Event [Member]	Subsequent Event [Member]
					Bristol-Myers Squibb Company [Member]
Business And Summary Of Significant Accounting Policies [Line Items]	'	'	'	'	'
Number of common stock issued through public offering	5,520,000	'	'	3,450,000	994,352
Aggrigate purchase price	$63,800,000	'	$63,849,000	$40,000,000	$21,000,000
Upfront payment	'	6,000,000	'	'	20,000,000
Research funding received	'	'	'	'	9,500,000
Research agreement term	'	'	'	'	'3 years
Collaboration arrangement, contingent payments	'	'	'	'	60,000,000
Total research funding	'	'	'	'	$240,000,000
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.
Price per share	'	'	'	'	$21.16