Loss Per Share - Schedule of Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Net loss	$ (28,276)	$ (23,634)	$ (25,683)	$ (21,940)	$ (19,066)	$ (22,702)	$ (22,219)	$ (21,356)	$ (99,533)	$ (85,343)	$ (67,543)
Weighted average shares outstanding, basic and diluted	49,350	48,554	45,814	45,234	44,215	43,161	42,836	42,043	47,247	43,069	36,006
Net loss per share, basic and diluted	$ (0.57)	$ (0.49)	$ (0.56)	$ (0.49)	$ (0.43)	$ (0.53)	$ (0.52)	$ (0.51)	$ (2.11)	$ (1.98)	$ (1.88)