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		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net loss	$ (22,219)	$ (15,593)	$ (43,575)	$ (28,224)
Weighted average shares outstanding, basic and diluted	42,836	34,916	42,441	34,820
Net loss per share, basic and diluted	$ (0.52)	$ (0.45)	$ (1.03)	$ (0.81)