Segment Information and Information about Geographic Areas - Property and Equipment, Net By Geographic Area (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment, net	$ 9,238	$ 8,589	$ 8,589
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment, net	7,876		7,182
Other [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment, net	$ 1,362		$ 1,407