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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net loss	$ (22,702)	$ (15,356)	$ (66,277)	$ (43,580)
Weighted average shares outstanding, basic and diluted	43,161	35,189	42,684	34,945
Net loss per share, basic and diluted	$ (0.53)	$ (0.44)	$ (1.55)	$ (1.25)