Net Loss per Share - Summary of Reconciliation of Denominator Used in Calculation of Basic and Diluted Net Loss Per Share (Detail) - 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
Earnings Per Share Basic And Diluted [Abstract]
Net loss	$ (10,515)	$ (13,552)	$ (31,733)	$ (35,802)
Weighted-average common shares outstanding — basic	35,393	33,819	35,038	32,901
Weighted-average common shares, outstanding — diluted	35,393	33,819	35,038	32,901
Net loss per share, basic and diluted	$ (0.30)	$ (0.40)	$ (0.91)	$ (1.09)