Five Prime Therapeutics (FPRX) 10-Q 13 Nov 13 2013 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2013	Oct. 31, 2013
Document And Entity Information [Abstract]	'	'
Document Type	'10-Q	'
Amendment Flag	'false	'
Document Period End Date	30-Sep-13	'
Document Fiscal Year Focus	'2013	'
Document Fiscal Period Focus	'Q3	'
Trading Symbol	'FPRX	'
Entity Registrant Name	'FIVE PRIME THERAPEUTICS INC	'
Entity Central Index Key	'0001175505	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Non-accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	16,833,697

Condensed_Balance_Sheets

Condensed Balance Sheets (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Current assets:	'	'
Cash and cash equivalents	$77,648	$11,391
Marketable securities	8,989	26,624
Receivable from collaborative partners	383	397
Prepaid and other current assets	866	689
Total current assets	87,886	39,101
Property and equipment, net	3,976	4,631
Other long-term assets	184	359
Total assets	92,046	44,091
Liabilities, convertible preferred stock and stockholders' equity (deficit)	'	'
Accounts payable	3,760	2,470
Accrued personnel-related expenses	2,096	2,250
Other accrued liabilities	685	303
Preferred stock warrant liability	'	563
Deferred revenue, current portion	9,015	7,498
Deferred rent, current portion	354	'
Total current liabilities	15,910	13,084
Deferred revenue, long-term portion	8,418	7,258
Deferred rent, long-term portion	2,283	2,448
Other long-term liabilities	729	897
Commitments	'	'
Common stock	17	1
Preferred stock	'	'
Additional paid-in capital	208,945	6,816
Accumulated other comprehensive income	1	7
Accumulated deficit	-144,257	-122,702
Total stockholders' equity (deficit)	64,706	-115,878
Total liabilities, convertible preferred stock and stockholders' equity (deficit)	92,046	44,091
Convertible preferred stock [Member]	'	'
Liabilities, convertible preferred stock and stockholders' equity (deficit)	'	'
Preferred stock	'	$136,282

Condensed_Statements_of_Operat

Condensed Statements of Operations (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Statement [Abstract]	'	'	'	'
Collaboration revenue	$3,482	$2,862	$10,006	$7,059
Operating expenses:	'	'	'	'
Research and development	8,193	6,510	24,708	21,300
General and administrative	2,607	2,257	7,385	6,696
Total operating expenses	10,800	8,767	32,093	27,996
Loss from operations	-7,318	-5,905	-22,087	-20,937
Interest income	7	21	35	70
Other income, net	77	26	497	85
Net loss	($7,234)	($5,858)	($21,555)	($20,782)
Basic and diluted net loss per common share	($2.74)	($4.85)	($12.60)	($17.46)
Shares used to compute basic and diluted net loss per common share	2,637	1,207	1,711	1,190

Condensed_Statements_of_Compre

Condensed Statements of Comprehensive Loss (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement Of Income And Comprehensive Income [Abstract]	'	'	'	'
Net loss	($7,234)	($5,858)	($21,555)	($20,782)
Other comprehensive loss:	'	'	'	'
Net unrealized gain (loss) on marketable securities	'	9	-6	-6
Comprehensive loss	($7,234)	($5,849)	($21,561)	($20,788)

Condensed_Statement_of_Cash_Fl

Condensed Statement of Cash Flows (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Operating activities	'	'
Net loss	($21,555)	($20,782)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:	'	'
Depreciation and amortization	1,288	1,226
Gain on disposal of property and equipment	'	-5
Stock-based compensation expense	1,554	1,237
Amortization of premium on marketable securities	272	416
Revaluation of preferred stock warrant liability	-500	-82
Changes in operating assets and liabilities:	'	'
Receivable from collaborative partners	14	767
Prepaid, other current assets, and other long-term assets	-2	211
Accounts payable	467	-519
Accrued personnel-related expenses	-154	-431
Payable to collaborative partner	'	-3,000
Deferred revenue	2,677	8,193
Deferred rent	189	373
Other accrued liabilities and other long-term liabilities	18	-208
Net cash used in operating activities	-15,732	-12,604
Investing activities	'	'
Purchases of marketable securities	-12,078	-36,058
Maturities of marketable securities	29,435	48,636
Purchases of property and equipment	-633	-501
Restricted cash	'	38
Net cash provided by investing activities	16,724	12,115
Financing activities	'	'
Proceeds from issuances of common stock	64,887	'
Issuances of convertible preferred stock proceeds (net of issuance costs)	'	6,819
Proceeds from exercise of stock options	387	77
Payments under capital lease obligation	-9	-11
Net cash provided by financing activities	65,265	6,885
Net increase in cash and cash equivalents	66,257	6,396
Cash and cash equivalents at beginning of period	11,391	4,361
Cash and cash equivalents at end of period	77,648	10,757
Supplemental schedule of noncash financing activities	'	'
Accrued and deferred offering costs	$1,026	'

Description_of_Business

Description of Business	9 Months Ended
	Sep. 30, 2013
Accounting Policies [Abstract]	'
Description of Business	'
	1. Description of Business
	Five Prime Therapeutics, Inc. (we, us, our, or the Company) is a clinical-stage biotechnology company focused on discovering and developing novel protein therapeutics. Protein therapeutics are antibodies or drugs developed from extracellular proteins or protein fragments that block disease processes, including cancer and inflammatory diseases. We were incorporated in December 2001 in Delaware. Our operations are based in South San Francisco, California and we operate in one segment.
	Unaudited Interim Financial Information
	The accompanying financial information as of September 30, 2013 is unaudited. The Condensed Financial Statements included in this report reflect all adjustments (consisting only of normal recurring adjustments) that our management considers necessary for the fair statement of the results of operations for the interim periods covered and of the financial condition of the Company at the date of the interim balance sheet. The December 31, 2012 Condensed Balance Sheet was derived from audited financial statements, but does not include all disclosures required by generally accepted accounting principles in the United States of America, or GAAP. The results for interim periods are not necessarily indicative of the results for the entire year or any other interim period. The accompanying Condensed Financial Statements and related financial information should be read in conjunction with the audited financial statements and the related notes thereto for the year ended December 31, 2012 included in the Company’s prospectus filed pursuant to Rule 424(b)(4) on September 18, 2013 with the U.S. Securities and Exchange Commission.
	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 $63.9 million, after underwriting discounts, commissions and estimated offering expenses. In addition, in connection with the completion of our IPO, all convertible preferred stock converted into common stock.

Summary_of_Significant_Account

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2013
Accounting Policies [Abstract]	'
Summary of Significant Accounting Policies	'
	2. Summary of Significant Accounting Policies
	Use of Estimates
	The preparation of financial statements in conformity with 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.
	Fair Value of Financial Instruments
	We determine the fair value of financial and nonfinancial assets and liabilities using the fair value hierarchy, which describes three levels of inputs that may be used to measure fair value, as follows:
	Level 1—Quoted prices in active markets for identical assets or liabilities;
	Level 2—Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities, quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities; and
	Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.
	We determine the fair value of Level 1 assets using quoted prices in active markets for identical assets. We review trading activity and pricing for Level 2 investments as of each measurement date. Level 2 inputs, obtained from various third-party data providers, represent quoted prices for similar assets in active markets, were derived from observable market data, or, if not directly observable, were derived from or corroborated by other observable market data.
	In certain cases where there is limited activity or less transparency around inputs to valuation, we classify securities as Level 3 within the valuation hierarchy. As of December 31, 2012, our Level 3 liability consists of a preferred stock warrant liability that we measured at estimated 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):
		SEPTEMBER 30, 2013
					BASIS OF FAIR VALUE
					MEASUREMENTS
		TOTAL			LEVEL 1			LEVEL 2		LEVEL 3
	Assets
	Money market funds	$	75,463		$	75,463		$	—	$	—
	U.S. government agency securities		9,740			—			9,740		—
	Total cash equivalents and marketable securities	$	85,203		$	75,463		$	9,740	$	—
		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
	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 Condensed 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, expiring in January 2014. 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 Condensed Statement of Operations and reclassified the fair value of $6,000 to permanent equity.
	The change in the estimated fair value of the preferred stock warrant liability is summarized below (in thousands):
		NINE MONTHS ENDED
		SEPTEMBER 30,
		2013			2012
	Balance, beginning	$	563		$	682
	Change in fair value recorded in other income, net		(500	)		(82	)
	Exercises		(57	)		—
	Conversion of preferred stock warrant to common stock warrants and reclassification to permanent equity		(6	)		—
	Balance, ending	$	—		$	600
	As of September 30, 2012, the fair value of the above warrants was determined using the following assumptions:
	Risk-free interest rate		0.1-0.4	%
	Estimated term (years)		2.3
	Volatility		85	%
	Net Loss Per Share of Common Stock
	We compute basic net loss per common share dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period. We did not include potentially dilutive securities consisting of stock options, the preferred stock warrants, the common stock warrant and convertible preferred stock in the diluted net loss per common share calculations for all periods presented, because the inclusion of such shares would have had an antidilutive effect. The convertible preferred stock contains certain participation rights.
	For the three months and nine months ended September 30, 2013 and 2012, we excluded the following securities from the calculation of diluted net loss per share as the effect would have been antidilutive (in thousands):
		SEPTEMBER 30,
		2013			2012
	Convertible preferred stock		—			9,929
	Options to purchase common stock		2,235			2,526
	Warrants to purchase common stock		2			—
	Warrants to purchase convertible preferred stock		—			88
			2,237			12,543

Cash_Equivalents_and_Marketabl

Cash Equivalents and Marketable Securities	9 Months Ended
	Sep. 30, 2013
Cash And Cash Equivalents [Abstract]	'
Cash Equivalents and Marketable Securities	'
	3. Cash Equivalents and Marketable Securities
	The following is a summary of our cash equivalents and marketable securities (in thousands):
		SEPTEMBER 30, 2013
		AMORTIZED			UNREALIZED		UNREALIZED		ESTIMATED
		COST BASIS			GAINS		LOSSES		FAIR VALUE
		(unaudited)
	Money market funds	$	75,463		$	—	$	—	$	75,463
	U.S. government agency securities		9,739			1		—		9,740
			85,202			1		—		85,203
	Less: cash equivalents		(76,214	)		—		—		(76,214	)
	Total marketable securities	$	8,988		$	1	$	—	$	8,989
		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 September 30, 2013 and December 31, 2012, the contractual maturities of our marketable securities were less than one year. There were no sales of available-for-sale securities in any of the periods presented.

Conversion_of_Convertible_Pref

Conversion of Convertible Preferred Stock	9 Months Ended
	Sep. 30, 2013
Equity [Abstract]	'
Conversion of Convertible Preferred Stock	'
	4. Conversion of 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.

Equity_Incentive_Plans

Equity Incentive Plans	9 Months Ended
	Sep. 30, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'
Equity Incentive Plans	'
	5. Equity Incentive 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.
	As of September 30, 2013, the total 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. As of September 30, 2013, no shares of common stock were subject to outstanding awards under the 2013 Plan.
	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 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. As of September 30, 2013, we have not issued any shares of common stock under the ESPP.
	The following table summarizes option activity under our stock plans and related information:
					OPTIONS OUTSTANDING
		NUMBER			NUMBER			WEIGHTED-
		OF SHARES			OF SHARES			AVERAGE
		AVAILABLE						EXERCISE
		FOR GRANT						PRICE
								PER SHARE
	Balance at December 31, 2012		451,349			2,545,231		$	5.17
	Options authorized		2,876,226			—			—
	Options granted		(547,909	)		547,909		$	6.87
	Options exercised		—			(138,484	)	$	2.79
	Options forfeited		53,246			(53,246	)	$	6.87
	Options expired		667,088			(667,088	)	$	4.1
	Balance at September 30, 2013		3,500,000			2,234,322		$	6
	Options exercisable					1,196,206		$	5.34
	As of September 30, 2013, options to purchase 2,177,736 shares of common stock were outstanding that are vested and therefore exercisable with a weighted-average exercise price of $5.98 per share and a weighted-average remaining contractual term of 7.5 years. As of September 30, 2013, the weighted-average remaining contractual term for outstanding options that are vested and therefore exercisable was 6.3 years. The aggregate intrinsic value of options outstanding was $15.9 million. The aggregate intrinsic value of outstanding options that are exercisable was $9.3 million. We calculated the aggregate intrinsic value as the difference between the exercise price of the options and the closing price of common stock of $13.10 per share as of September 30, 2013.
	Stock Based Compensation
	We calculated employee stock-based compensation expense based on awards ultimately expected to vest reduced by estimated forfeitures. We estimate forfeitures at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. Total stock-based compensation expense recognized was as follows (in thousands):
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
		2013			2012			2013			2012
	Research and development	$	261		$	177		$	661		$	480
	General and administrative		258			315			893			757
	Total	$	519		$	492		$	1,554		$	1,237
	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.
	We estimated the fair value of each stock option using the Black-Scholes option-pricing model based on the date of grant of such stock option with the following weighted-average assumptions:
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
		2013			2012			2013			2012
	Expected term (years)		5.3-6.1			5.0-6.1			5.0-6.1			5.0-6.1
	Expected volatility		85	%		85	%		85	%		85	%
	Risk-free interest rate		1.4-1.6	%		0.6-0.8	%		0.8-1.6	%		0.6-1.1	%
	Expected dividend yield		0	%		0	%		0	%		0	%
	As of September 30, 2013, we had $4.6 million of total unrecognized compensation expense related to nonvested employee and director stock options that we expect to recognize over a weighted-average period of 2.9 years.

Collaborative_Research_and_Dev

Collaborative Research and Development Agreements	9 Months Ended
	Sep. 30, 2013
Organization Consolidation And Presentation Of Financial Statements [Abstract]	'
Collaborative Research and Development Agreements	'
	6. Collaborative Research and Development Agreements
	UCB Pharma S.A.
	In March 2013, we and UCB Pharma S.A., or 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 the Financial Accounting Standards Board Accounting Standards Update, or 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.
	During the three and nine months ended September 30, 2013, we recognized $0.6 million and $1.4 million, respectively, of revenue under this arrangement. As of September 30, 2013, we have deferred revenue relating to this collaboration agreement of $6.8 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.
	GlaxoSmithKline
	Muscle Diseases Discovery Collaboration
	In July 2010, we entered into a research collaboration and license agreement with GlaxoSmithKline LLC, or GSK US, to identify potential drug targets and drug candidates to treat skeletal muscle diseases. In December 2012, GSK US selected a protein target for further evaluation under the collaboration agreement. In September 2013, we and GSK US entered into an agreement to extend by approximately eight months the evaluation period for this protein target. In connection with the extension of the evaluation period, GSK US agreed to pay a $0.2 million extension fee. We are recognizing the $0.2 million extension fee over the eight-month extension period, which we recorded as accounts receivable as of September 30, 2013.

Subsequent_Events

Subsequent Events	9 Months Ended
	Sep. 30, 2013
Subsequent Events [Abstract]	'
Subsequent Events	'
	7. Subsequent Events
	In October 2013, GSK US exercised its right to reserve for further evaluation several protein therapeutic targets for muscle diseases that we discovered in our muscle diseases discovery collaboration with GSK US. In connection with reserving these targets for further evaluation, GSK US will pay us a selection fee of $0.3 million.

Description_of_Business_Polici

Description of Business (Policies)	9 Months Ended
	Sep. 30, 2013
Accounting Policies [Abstract]	'
Unaudited Interim Financial Information	'
	Unaudited Interim Financial Information
	The accompanying financial information as of September 30, 2013 is unaudited. The Condensed Financial Statements included in this report reflect all adjustments (consisting only of normal recurring adjustments) that our management considers necessary for the fair statement of the results of operations for the interim periods covered and of the financial condition of the Company at the date of the interim balance sheet. The December 31, 2012 Condensed Balance Sheet was derived from audited financial statements, but does not include all disclosures required by generally accepted accounting principles in the United States of America, or GAAP. The results for interim periods are not necessarily indicative of the results for the entire year or any other interim period. The accompanying Condensed Financial Statements and related financial information should be read in conjunction with the audited financial statements and the related notes thereto for the year ended December 31, 2012 included in the Company’s prospectus filed pursuant to Rule 424(b)(4) on September 18, 2013 with the U.S. Securities and Exchange Commission.
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 $63.9 million, after underwriting discounts, commissions and estimated 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.
Fair Value of Financial Instruments	'
	Fair Value of Financial Instruments
	We determine the fair value of financial and nonfinancial assets and liabilities using the fair value hierarchy, which describes three levels of inputs that may be used to measure fair value, as follows:
	Level 1—Quoted prices in active markets for identical assets or liabilities;
	Level 2—Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities, quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities; and
	Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.
	We determine the fair value of Level 1 assets using quoted prices in active markets for identical assets. We review trading activity and pricing for Level 2 investments as of each measurement date. Level 2 inputs, obtained from various third-party data providers, represent quoted prices for similar assets in active markets, were derived from observable market data, or, if not directly observable, were derived from or corroborated by other observable market data.
	In certain cases where there is limited activity or less transparency around inputs to valuation, we classify securities as Level 3 within the valuation hierarchy. As of December 31, 2012, our Level 3 liability consists of a preferred stock warrant liability that we measured at estimated 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):
		SEPTEMBER 30, 2013
					BASIS OF FAIR VALUE
					MEASUREMENTS
		TOTAL			LEVEL 1			LEVEL 2		LEVEL 3
	Assets
	Money market funds	$	75,463		$	75,463		$	—	$	—
	U.S. government agency securities		9,740			—			9,740		—
	Total cash equivalents and marketable securities	$	85,203		$	75,463		$	9,740	$	—
		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
	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 Condensed 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, expiring in January 2014. 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 Condensed Statement of Operations and reclassified the fair value of $6,000 to permanent equity.
	The change in the estimated fair value of the preferred stock warrant liability is summarized below (in thousands):
		NINE MONTHS ENDED
		SEPTEMBER 30,
		2013			2012
	Balance, beginning	$	563		$	682
	Change in fair value recorded in other income, net		(500	)		(82	)
	Exercises		(57	)		—
	Conversion of preferred stock warrant to common stock warrants and reclassification to permanent equity		(6	)		—
	Balance, ending	$	—		$	600
	As of September 30, 2012, the fair value of the above warrants was determined using the following assumptions:
	Risk-free interest rate		0.1-0.4	%
	Estimated term (years)		2.3
	Volatility		85	%
Net Loss Per Share of Common Stock	'
	Net Loss Per Share of Common Stock
	We compute basic net loss per common share dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period. We did not include potentially dilutive securities consisting of stock options, the preferred stock warrants, the common stock warrant and convertible preferred stock in the diluted net loss per common share calculations for all periods presented, because the inclusion of such shares would have had an antidilutive effect. The convertible preferred stock contains certain participation rights.
	For the three months and nine months ended September 30, 2013 and 2012, we excluded the following securities from the calculation of diluted net loss per share as the effect would have been antidilutive (in thousands):
		SEPTEMBER 30,
		2013			2012
	Convertible preferred stock		—			9,929
	Options to purchase common stock		2,235			2,526
	Warrants to purchase common stock		2			—
	Warrants to purchase convertible preferred stock		—			88
			2,237			12,543

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 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):
		SEPTEMBER 30, 2013
					BASIS OF FAIR VALUE
					MEASUREMENTS
		TOTAL			LEVEL 1			LEVEL 2		LEVEL 3
	Assets
	Money market funds	$	75,463		$	75,463		$	—	$	—
	U.S. government agency securities		9,740			—			9,740		—
	Total cash equivalents and marketable securities	$	85,203		$	75,463		$	9,740	$	—
		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):
		NINE MONTHS ENDED
		SEPTEMBER 30,
		2013			2012
	Balance, beginning	$	563		$	682
	Change in fair value recorded in other income, net		(500	)		(82	)
	Exercises		(57	)		—
	Conversion of preferred stock warrant to common stock warrants and reclassification to permanent equity		(6	)		—
	Balance, ending	$	—		$	600
Fair Value of Warrants Assumptions	'
	As of September 30, 2012, the fair value of the above warrants was determined using the following assumptions:
	Risk-free interest rate		0.1-0.4	%
	Estimated term (years)		2.3
	Volatility		85	%
Securities Excluded from Calculation of Diluted Net Loss Per Share	'
	For the three months and nine months ended September 30, 2013 and 2012, we excluded the following securities from the calculation of diluted net loss per share as the effect would have been antidilutive (in thousands):
		SEPTEMBER 30,
		2013			2012
	Convertible preferred stock		—			9,929
	Options to purchase common stock		2,235			2,526
	Warrants to purchase common stock		2			—
	Warrants to purchase convertible preferred stock		—			88
			2,237			12,543

Cash_Equivalents_and_Marketabl1

Cash Equivalents and Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 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 (in thousands):
		SEPTEMBER 30, 2013
		AMORTIZED			UNREALIZED		UNREALIZED		ESTIMATED
		COST BASIS			GAINS		LOSSES		FAIR VALUE
		(unaudited)
	Money market funds	$	75,463		$	—	$	—	$	75,463
	U.S. government agency securities		9,739			1		—		9,740
			85,202			1		—		85,203
	Less: cash equivalents		(76,214	)		—		—		(76,214	)
	Total marketable securities	$	8,988		$	1	$	—	$	8,989
		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

Equity_Incentive_Plans_Tables

Equity Incentive Plans (Tables)	9 Months Ended
	Sep. 30, 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			NUMBER			WEIGHTED-
		OF SHARES			OF SHARES			AVERAGE
		AVAILABLE						EXERCISE
		FOR GRANT						PRICE
								PER SHARE
	Balance at December 31, 2012		451,349			2,545,231		$	5.17
	Options authorized		2,876,226			—			—
	Options granted		(547,909	)		547,909		$	6.87
	Options exercised		—			(138,484	)	$	2.79
	Options forfeited		53,246			(53,246	)	$	6.87
	Options expired		667,088			(667,088	)	$	4.1
	Balance at September 30, 2013		3,500,000			2,234,322		$	6
	Options exercisable					1,196,206		$	5.34
Schedule of Stock-Based Compensation Expenses Recognized	'
	Total stock-based compensation expense recognized was as follows (in thousands):
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
		2013			2012			2013			2012
	Research and development	$	261		$	177		$	661		$	480
	General and administrative		258			315			893			757
	Total	$	519		$	492		$	1,554		$	1,237
Schedule of Stock Option Weighted-Average Assumptions	'
	We estimated the fair value of each stock option using the Black-Scholes option-pricing model based on the date of grant of such stock option with the following weighted-average assumptions:
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
		2013			2012			2013			2012
	Expected term (years)		5.3-6.1			5.0-6.1			5.0-6.1			5.0-6.1
	Expected volatility		85	%		85	%		85	%		85	%
	Risk-free interest rate		1.4-1.6	%		0.6-0.8	%		0.8-1.6	%		0.6-1.1	%
	Expected dividend yield		0	%		0	%		0	%		0	%

Description_of_Business_Additi

Description of Business - Additional Information (Detail) (USD $)	9 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013
	Segment
Organization Consolidation And Presentation Of Financial Statements [Abstract]	'
Number of operating segments	1
Number of common stock issued through IPO	5,520,000
Net proceeds after underwriting discounts, commissions and estimated offering expenses	$64,887

Summary_of_Significant_Account2

Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	1 Months Ended	9 Months Ended
	Sep. 04, 2013	Sep. 30, 2013
Temporary Equity [Line Items]	'	'
Reverse stock split	'1-for-12.3	'
Net number of warrants exercised	'	4,376
Gain (Loss) related the change in fair value of other income	'	$83,000
Reclassification of warrant liability to permanent equity	'	57,000
Outstanding warrant converted into a warrant to purchase, per share	'	13
Reclassification of warrant liability to equity	'	6,000
Series A convertible preferred stock [Member]	'	'
Temporary Equity [Line Items]	'	'
Gain (Loss) related the change in fair value of other income	'	($3,000)
Outstanding warrant converted into a warrant to purchase, per share	'	12.3
Outstanding warrant converted into a warrant to purchase, number of shares	'	2,304
Outstanding warrant converted into a warrant to purchase, expiration	'	'January 2014

Summary_of_Significant_Account3

Summary of Significant Accounting Policies - Summary of Assets and Liabilities Recorded at Fair Value (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Preferred stock warrant liability [Member]	'	'
Liability:	'	'
Liability	'	$563
Preferred stock warrant liability [Member] | Level 3 [Member]	'	'
Liability:	'	'
Liability	'	563
Money market funds [Member]	'	'
Assets:	'	'
Assets	75,463	6,910
Money market funds [Member] | Level 1 [Member]	'	'
Assets:	'	'
Assets	75,463	6,910
Money market funds [Member] | Level 2 [Member]	'	'
Assets:	'	'
Assets	'	'
Money market funds [Member] | Level 3 [Member]	'	'
Assets:	'	'
Assets	'	'
U.S. Treasury securities [Member]	'	'
Assets:	'	'
Assets	'	3,577
U.S. Treasury securities [Member] | Level 1 [Member]	'	'
Assets:	'	'
Assets	'	3,577
U.S. government agency securities [Member]	'	'
Assets:	'	'
Assets	9,740	23,047
U.S. government agency securities [Member] | Level 1 [Member]	'	'
Assets:	'	'
Assets	'	'
U.S. government agency securities [Member] | Level 2 [Member]	'	'
Assets:	'	'
Assets	9,740	23,047
U.S. government agency securities [Member] | Level 3 [Member]	'	'
Assets:	'	'
Assets	'	'
Total cash equivalents and marketable securities [Member]	'	'
Assets:	'	'
Assets	85,203	33,534
Total cash equivalents and marketable securities [Member] | Level 1 [Member]	'	'
Assets:	'	'
Assets	75,463	10,487
Total cash equivalents and marketable securities [Member] | Level 2 [Member]	'	'
Assets:	'	'
Assets	9,740	23,047
Total cash equivalents and marketable securities [Member] | Level 3 [Member]	'	'
Assets:	'	'
Assets	'	'

Summary_of_Significant_Account4

Summary of Significant Accounting Policies - Change in Estimated Fair Value of Preferred Stock Warrant Liability (Detail) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Fair Value Disclosures [Abstract]	'	'
Balance, beginning	$563	$682
Change in fair value recorded in other income, net	-500	-82
Exercises	-57	'
Conversion of preferred stock warrant to common stock warrants and reclassification to permanent equity	-6	'
Balance, ending	'	$600

Summary_of_Significant_Account5

Summary of Significant Accounting Policies - Fair Value of Warrants Assumptions (Detail)	9 Months Ended
	Sep. 30, 2013
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]	'
Estimated term (years)	'2 years 3 months 18 days
Volatility	85.00%
Minimum [Member]	'
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]	'
Risk-free interest rate	0.10%
Maximum [Member]	'
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]	'
Risk-free interest rate	0.40%

Summary_of_Significant_Account6

Summary of Significant Accounting Policies - Securities Excluded from Calculation of Diluted Net Loss Per Share (Detail)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Dilutive Securities Included And Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'
Securities excluded from calculation of diluted net loss per share	2,237	12,543
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 per share	'	9,929
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 per share	2,235	2,526
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 per share	2	'
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 per share	'	88

Cash_Equivalents_and_Marketabl2

Cash Equivalents and Marketable Securities - Summary of Cash Equivalents and Marketable Securities (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]	'	'
AMORTIZED COST BASIS	$8,988	$26,617
UNREALIZED GAINS	1	7
UNREALIZED LOSSES	'	'
ESTIMATED FAIR VALUE	8,989	26,624
Money market funds [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
AMORTIZED COST BASIS	75,463	6,910
UNREALIZED GAINS	'	'
UNREALIZED LOSSES	'	'
ESTIMATED FAIR VALUE	75,463	6,910
U.S. Treasury securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
AMORTIZED COST BASIS	'	3,576
UNREALIZED GAINS	'	1
UNREALIZED LOSSES	'	'
ESTIMATED FAIR VALUE	'	3,577
U.S. government agency securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
AMORTIZED COST BASIS	9,739	23,041
UNREALIZED GAINS	1	6
UNREALIZED LOSSES	'	'
ESTIMATED FAIR VALUE	9,740	23,047
Marketable securities including cash equivalents [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
AMORTIZED COST BASIS	85,202	33,527
UNREALIZED GAINS	1	7
UNREALIZED LOSSES	'	'
ESTIMATED FAIR VALUE	85,203	33,534
Cash equivalents [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
AMORTIZED COST BASIS	-76,214	-6,910
UNREALIZED GAINS	'	'
UNREALIZED LOSSES	'	'
ESTIMATED FAIR VALUE	($76,214)	($6,910)

Cash_Equivalents_and_Marketabl3

Cash Equivalents and Marketable Securities - Additional Information (Detail) (Marketable securities [Member])	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Marketable securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Maximum contractual maturity term	'1 year	'1 year

Conversion_of_Convertible_Pref1

Conversion of Convertible Preferred Stock - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2013
Temporary Equity Disclosure [Abstract]	'
Preferred stock converted into common stock	9,929,159

Equity_Incentive_Plans_Additio

Equity Incentive Plans - Additional Information (Detail) (USD $)	1 Months Ended	9 Months Ended		9 Months Ended		1 Months Ended		1 Months Ended
	Mar. 31, 2013	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013	Sep. 23, 2013	Feb. 28, 2013	Feb. 28, 2013
				2013 Omnibus Incentive Plan [Member]	Prior Plans [Member]	2013 Employee Stock Purchase Plan [Member]	2013 Employee Stock Purchase Plan [Member]	Minimum [Member]	Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'	'	'	'	'	'
Common stock available for issuance	'	3,500,000	451,349	3,500,000	1,069,985	'	'	'	'
Percent of annual increase in common stock available for issuance	'	'	'	4.00%	'	1.00%	'	'	'
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. As of September 30, 2013, we have not issued any shares of common stock under the ESPP.	'	'	'
Stock options to purchase common stock outstanding, vested	'	2,177,736	'	'	'	'	'	'	'
Stock options to purchase common stock outstanding, weighted-average exercise price	'	$5.98	'	'	'	'	'	'	'
Options outstanding, weighted-average remaining contractual term	'	'7 years 6 months	'	'	'	'	'	'	'
Weighted-average remaining contractual term options exercisable	'	'6 years 3 months 18 days	'	'	'	'	'	'	'
Aggregate intrinsic value of options outstanding	'	$15,900,000	'	'	'	'	'	'	'
Aggregate intrinsic value of options exercisable	'	9,300,000	'	'	'	'	'	'	'
Closing price of common stock	'	$13.10	'	'	'	'	'	'	'
Option vested period	'	'	'	'	'	'	'	'18 months	'20 months
Additional incremental stock-based compensation	157,000	'	'	'	'	'	'	'	'
Total unrecognized compensation expense related to nonvested employee and director stock options	'	$4,600,000	'	'	'	'	'	'	'
Unrecognized compensation expense expected to recognize, weighted-average period	'	'2 years 10 months 24 days	'	'	'	'	'	'	'

Equity_Incentive_Plans_Schedul

Equity Incentive Plans - Schedule of Option Activity under Stock Plans and Related Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'
NUMBER OF SHARES AVAILABLE FOR GRANT, Beginning balance	451,349
NUMBER OF SHARES AVAILABLE FOR GRANT, Options authorized	2,876,226
NUMBER OF SHARES AVAILABLE FOR GRANT, Options granted	-547,909
NUMBER OF SHARES AVAILABLE FOR GRANT, Options exercised	'
NUMBER OF SHARES AVAILABLE FOR GRANT, Options forfeited	53,246
NUMBER OF SHARES AVAILABLE FOR GRANT, Options expired	667,088
NUMBER OF SHARES AVAILABLE FOR GRANT, Ending balance	3,500,000
NUMBER OF SHARES, Beginning balance	2,545,231
NUMBER OF SHARES, Options granted	547,909
NUMBER OF SHARES, Options exercised	-138,484
NUMBER OF SHARES, Options forfeited	-53,246
NUMBER OF SHARES, Options expired	-667,088
NUMBER OF SHARES, Ending balance	2,234,322
NUMBER OF SHARES, Options exercisable	1,196,206
WEIGHTED-AVERAGE EXERCISE PRICE PER SHARE, Options beginning balance	$5.17
WEIGHTED-AVERAGE EXERCISE PRICE PER SHARE, Options granted	$6.87
WEIGHTED-AVERAGE EXERCISE PRICE PER SHARE, Options exercised	$2.79
WEIGHTED-AVERAGE EXERCISE PRICE PER SHARE, Options forfeited	$6.87
WEIGHTED-AVERAGE EXERCISE PRICE PER SHARE, Options expired	$4.10
WEIGHTED-AVERAGE EXERCISE PRICE PER SHARE, Options ending balance	$6
WEIGHTED-AVERAGE EXERCISE PRICE PER SHARE, Option exercisable	$5.34

Equity_Incentive_Plans_Schedul1

Equity Incentive Plans - Schedule of Stock-Based Compensation Expenses Recognized (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'	'	'
Stock-based compensation expense recognized	$519	$492	$1,554	$1,237
Research and development [Member]	'	'	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'	'	'
Stock-based compensation expense recognized	261	177	661	480
General and administrative [Member]	'	'	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'	'	'
Stock-based compensation expense recognized	$258	$315	$893	$757

Equity_Incentive_Plans_Schedul2

Equity Incentive Plans - Schedule of Stock Option Weighted-Average Assumptions (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'
Expected volatility	85.00%	85.00%	85.00%	85.00%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Minimum [Member]	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'
Expected term (years)	'5 years 3 months 18 days	'5 years	'5 years	'5 years
Risk-free interest rate	1.40%	0.60%	0.80%	0.60%
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	'6 years 1 month 6 days
Risk-free interest rate	1.60%	0.80%	1.60%	1.10%

Collaborative_Research_and_Dev1

Collaborative Research and Development Agreements - Additional Information (Detail) (USD $)	1 Months Ended			3 Months Ended	9 Months Ended
In Millions, unless otherwise specified	Oct. 31, 2013	Sep. 30, 2013	Mar. 31, 2013	Sep. 30, 2013	Sep. 30, 2013
			Installment
Organization Consolidation And Presentation Of Financial Statements [Abstract]	'	'	'	'	'
Upfront payment	'	'	$6	'	'
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	0.3	'	'	'	0.4
Recognized revenue under collaboration arrangement	'	'	'	0.6	1.4
Deferred revenue relating to collaboration agreement	'	6.8	'	6.8	6.8
Extended evaluation period	'	'8 months	'	'	'
Extension fee	'	'	'	'	$0.20

Subsequent_Events_Additional_I

Subsequent Events - Additional Information (Detail) (USD $)	1 Months Ended	9 Months Ended
In Millions, unless otherwise specified	Oct. 31, 2013	Sep. 30, 2013
Subsequent Events [Abstract]	'	'
Selection fee	$0.30	$0.40