Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (USD $) In Thousands, except Share data, unless otherwise specified	0 Months Ended		12 Months Ended															1 Months Ended			1 Months Ended	2 Months Ended
	Dec. 02, 2013	Nov. 04, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Common Stock	Dec. 31, 2012 Common Stock	Dec. 31, 2011 Common Stock	Dec. 31, 2013 Additional Paid-in Capital	Dec. 31, 2012 Additional Paid-in Capital	Dec. 31, 2011 Additional Paid-in Capital	Dec. 31, 2013 Accumulated Deficit	Dec. 31, 2012 Accumulated Deficit	Dec. 31, 2011 Accumulated Deficit	Dec. 31, 2013 Convertible Preferred Stock	Dec. 31, 2011 Convertible Preferred Stock	Dec. 31, 2010 Convertible Preferred Stock	Jul. 31, 2011 Series B	Feb. 28, 2011 Series B	Dec. 31, 2012 Series B	Jun. 30, 2013 Series C	Dec. 31, 2012 Series C
Increase (Decrease) in Convertible Preferred Stock and Stockholders' Equity (Deficit)
Balance			$ 63,372												$ 63,372	$ 49,296	$ 30,674
Balance (in shares)			53,084,507												53,084,507	45,147,999	30,249,334			22,748,000
Balance			(58,471)	(40,766)	(26,811)	1	1	1	1,597	653	163	(60,069)	(41,420)	(26,975)
Balance (in shares)						667,684	594,941	556,844
Issuance of convertible preferred stock, net of issuance costs and preferred stock liability																		9,311	9,311		12,997	14,076
Issuance of convertible preferred stock, net of issuance costs and preferred stock liability (in shares)																		7,449,330	7,449,335		6,904,761	7,936,508
Extinguishment of the preferred stock liability															2,653
Issuance of common stock on exercise of stock options			552	76	24				552	76	24
Issuance of common stock on exercise of stock options (in shares)			377,966	72,743		377,966	72,743	38,097
Issuance of common stock in initial public offering, net of discounts and commissions of $4,642 and issuance costs of $2,507			59,156			5			59,151
Issuance of common stock in initial public offering, net of discounts and commissions of $4,642 and issuance costs of $2,507 (in shares)	100,351	5,000,000				5,100,351
Conversion of preferred stock into common stock upon initial public offering			(79,022)												(79,022)
Conversion of preferred stock into common stock upon initial public offering (in shares)		(59,989,268)													(59,989,268)
Conversion of preferred stock into common stock upon initial public offering			79,022			15			79,007
Conversion of preferred stock into common stock upon initial public offering (in shares)		14,997,312				14,997,312
Reclassification of preferred stock warrant liability into additional paid-in capital upon initial public offering			261						261
Stock-based compensation expense (employee)			1,041	590	378				1,041	590	378
Stock-based compensation expense (non employee)			206	85	88				206	85	88
Equity-based compensation			259	193					259	193
Common stock subject to repurchase			(3)						(3)
Net loss and comprehensive loss			(25,580)	(18,649)	(14,445)							(25,580)	(18,649)	(14,445)
Balance				63,372												49,296	30,674
Balance (in shares)			0	53,084,507												45,147,999	30,249,334			22,748,000		7,936,508
Balance			$ 56,443	$ (58,471)	$ (40,766)	$ 21	$ 1	$ 1	$ 142,071	$ 1,597	$ 653	$ (85,649)	$ (60,069)	$ (41,420)
Balance (in shares)						21,143,313	667,684	594,941