Net Loss Per Share of Common Stock - Calculation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator:
Net loss attributable to common stockholders	$ (401)	$ (3,617)	$ (5,855)	$ (11,074)	$ (2,418)	$ (28,622)	$ (5,240)	$ (6,950)	$ (20,947)	$ (43,230)	$ (23,489)
Denominator:
Weighted-average number of shares of common stock outstanding for basic and diluted net loss per share attributable to common stockholders	51,644,295	52,473,601	52,633,054	52,372,857	52,186,221	51,875,785	51,445,613	51,217,220	52,279,738	51,684,397	50,637,541
Basic and diluted net loss per share (in dollars per share)	$ (0.01)	$ (0.07)	$ (0.11)	$ (0.21)	$ (0.05)	$ (0.55)	$ (0.10)	$ (0.14)	$ (0.40)	$ (0.84)	$ (0.46)