Net Loss Per Share - Summary of Basic and Diluted Net Loss Per Share of Common Stock (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Net loss	$ (11,637)	$ (13,452)	$ (22,182)	$ (29,032)
Weighted-average common shares outstanding, basic and diluted	42,681,287	41,063,613	42,395,450	40,805,641
Net loss per share, basic and diluted (in dollars per share)	$ (0.27)	$ (0.33)	$ (0.52)	$ (0.71)