Summary of Significant Accounting Policies - Reconciliation of the Numerator and Denominator used in Computing Basic and Diluted Net Income (Loss) Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator:
Net income (loss)	$ (1,673)	$ 900	$ 297
Less: Accretion of preferred stock	(6,258)	(11,301)	(11,301)
Net loss attributable to common stockholders	$ (7,931)	$ (10,401)	$ (11,004)
Denominator:
Weighted-average common shares outstanding	10,904	4,067	3,489
Weighted-average unvested shares of common stock subject to repurchase	(126)	(174)	(151)
Weighted-average shares used to compute net loss per share attributable to common stockholders—basic and diluted	10,778	3,893	3,338
Net loss per share attributable to common stockholders — basic and diluted	$ (0.74)	$ (2.67)	$ (3.30)