Net Income (Loss) Per Share Attributable to Common Stockholders - Reconciliation of the Numerator and Denominator used in Computing Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Numerator:
Net income (loss)	$ 808	$ 13	$ (1,776)	$ 82
Less: Accretion of preferred stock	(608)	(2,826)	(6,258)	(8,476)
Net income (loss) attributable to common stockholders — basic and diluted	$ 200	$ (2,813)	$ (8,034)	$ (8,394)
Weighted-average shares used to compute net income (loss) per share attributable to common stockholders:
Weighted-average common shares outstanding	15,460	4,065	8,117	3,997
Weighted-average unvested shares of common stock subject to repurchase	(142)	(161)	(126)	(184)
Weighted-average shares used to compute net income (loss) per share attributable to common stockholders — basic	15,318	3,904	7,991	3,813
Effects of potentially dilutive securities:
Weighted-average unvested shares of common stock subject to repurchase	141
Stock options	1,400
Weighted-average shares used to compute net income (loss) per share attributable to common stockholders — diluted	16,859	3,904	7,991	3,813
Net income (loss) per share attributable to common stockholders:
Basic	$ 0.01	$ (0.72)	$ (1.01)	$ (2.20)
Diluted	$ 0.01	$ (0.72)	$ (1.01)	$ (2.20)