Segment And Geographic Information - Schedule of Property and Equipment, Net, by Geographical Area (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Property and equipment, net	$ 34,442	$ 38,855	$ 3,748
U.S.
Segment Reporting Information [Line Items]
Property and equipment, net	32,862	36,891	3,219
Europe
Segment Reporting Information [Line Items]
Property and equipment, net	1,019	1,252	529
Asia and other
Segment Reporting Information [Line Items]
Property and equipment, net	$ 561	$ 712	$ 0