Net Loss per Share - Computation of Basic and Diluted Net Loss per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net loss	$ (16,509)	$ (25,068)	$ (28,922)	$ (32,842)	$ (22,960)	$ (21,960)	$ (70,499)	$ (77,762)
Weighted-average common shares outstanding:
Basic and Diluted	46,885,424			44,517,134			46,803,659	41,314,044
Net loss per share, Basic and Diluted	$ (0.35)			$ (0.74)			$ (1.51)	$ (1.88)