Loss Per Share - Schedule of Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net loss	$ (21,940)	$ (21,356)
Weighted average shares outstanding, basic and diluted	45,234,326	42,042,586
Net loss per share, basic and diluted	$ (0.49)	$ (0.51)