Background and Organization - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Net loss	$ (33,361)	$ (4,814)
Net cash used from operating activities	(23,653)	$ (37,454)
Cash and cash equivalents	$ 145,797		$ 167,432