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						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net loss	$ (23,634)	$ (25,683)	$ (21,940)	$ (22,702)	$ (22,219)	$ (21,356)	$ (71,257)	$ (66,277)
Weighted average shares outstanding, basic and diluted	48,554			43,161			46,547	42,684
Net loss per share, basic and diluted	$ (0.49)			$ (0.53)			$ (1.53)	$ (1.55)