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, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net loss	$ (22,960)	$ (21,960)	$ (17,194)	$ (16,767)	$ (44,920)	$ (33,961)
Weighted-average common shares outstanding:
Basic and Diluted	39,818,162		33,315,809		39,685,954	33,000,487
Net loss per share, Basic and Diluted	$ (0.58)		$ (0.52)		$ (1.13)	$ (1.03)