Convertible Preferred Stock and Stockholders' Equity (Deficit) - Summary of Common Stock Reserved for Future Issuance (Detail) - shares	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Equity [Abstract]
Warrants exercisable, outstanding	149,704	149,704	149,704
Common stock options issued and outstanding	2,464,849	1,859,034
Common stock authorized for future option grants	593,531	403,859
Common stock authorized for the ESPP	432,086	300,000
Total	3,640,170	2,712,597