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
	Mar. 31, 2016	Mar. 31, 2015
Numerator
Net loss	$ (8,420)	$ (4,500)
Cumulative dividend relating to redeemable convertible preferred stock		(952)
Accretion of redeemable convertible preferred stock to redemption value		(33)
Net loss attributable to common stockholders	$ (8,420)	$ (5,485)
Denominator
Weighted average shares outstanding	27,024,638	3,752,389
Less: weighted average shares subject to repurchase	(855,486)	(1,530,638)
Weighted average shares used to compute basic and diluted net loss per share	26,169,152	2,221,751
Net loss per share attributable to common stockholders:
Basic and diluted	$ (0.32)	$ (2.47)