Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, cost	$ 834,232	$ 809,371
Accumulated depreciation	(709,056)	(664,484)
Property and equipment, net	125,176	144,887	$ 161,509
Computer hardware
Property, Plant and Equipment [Line Items]
Property and equipment, cost	177,237	171,515
Computer software
Property, Plant and Equipment [Line Items]
Property and equipment, cost	378,734	376,761
Furniture and equipment
Property, Plant and Equipment [Line Items]
Property and equipment, cost	107,421	102,424
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, cost	160,521	148,764
Other
Property, Plant and Equipment [Line Items]
Property and equipment, cost	$ 10,319	$ 9,907