Net Loss per Share Attributable to Common Stockholders - Computation of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Numerator
Net loss	$ (9,231)	$ (5,462)	$ (27,411)	$ (15,037)
Cumulative dividends on redeemable convertible preferred stock		(1,900)		(4,530)
Accretion of redeemable convertible preferred stock to redemption value		(26)		(88)
Net loss attributable to common stockholders	$ (9,231)	$ (7,388)	$ (27,411)	$ (19,655)
Denominator
Weighted average shares outstanding	27,023,650	3,923,228	27,023,951	3,846,864
Less: weighted average shares subject to repurchase	(553,352)	(1,268,863)	(692,099)	(1,382,988)
Weighted average shares used to compute basic and diluted net loss per share	26,470,298	2,654,365	26,331,852	2,463,876
Net loss per share attributable to common stockholders:
Basic and diluted	$ (0.35)	$ (2.78)	$ (1.04)	$ (7.98)