Geographical Information - Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment, net	$ 266,589	$ 269,439	$ 273,221
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment, net	263,037	267,324	269,721
All Other Countries [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment, net	$ 3,552	$ 2,115	$ 3,500