Property and Equipment, Net - Components of Property and Equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, cost	$ 822,371	$ 809,371
Accumulated depreciation	(697,196)	(664,484)
Property and equipment, net	125,175	144,887
Computer hardware
Property, Plant and Equipment [Line Items]
Property and equipment, cost	173,082	171,515
Computer software
Property, Plant and Equipment [Line Items]
Property and equipment, cost	379,605	376,761
Furniture and equipment
Property, Plant and Equipment [Line Items]
Property and equipment, cost	105,123	102,424
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, cost	154,272	148,764
Other
Property, Plant and Equipment [Line Items]
Property and equipment, cost	$ 10,289	$ 9,907