Net Loss per Share - Computation of Basic and Diluted Net Loss per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net loss	$ (17,194)	$ (9,300)	$ (33,961)	$ (31,504)
Weighted-average common shares outstanding:
Basic and Diluted	33,315,809	32,239,877	33,000,487	29,783,424
Net loss per share, Basic and Diluted	$ (0.52)	$ (0.29)	$ (1.03)	$ (1.06)