Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property Plant And Equipment [Abstract]
Depreciation	$ 2,008	$ 1,151	$ 238
Property and equipment disposals	0	2,700	200
Gain (Loss) on sale of property and equipment	$ 0	$ (2,300)	$ (100)