Property and Equipment, Net - Components of Property and Equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Computer hardware	$ 172,231	$ 170,746
Computer software	375,447	374,490
Furniture and equipment	103,115	100,472
Leasehold improvements	144,591	133,541
Other	9,702	9,993
Property and equipment, cost	805,086	789,242
Accumulated depreciation	(658,479)	(627,733)
Property and equipment, net	$ 146,607	$ 161,509