Property and Equipment, Net - Components of Property and Equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property and equipment, cost	$ 652,989	$ 665,684
Accumulated depreciation	(559,973)	(555,867)
Property and equipment, net	93,016	109,817
Computer hardware
Property, Plant and Equipment [Line Items]
Property and equipment, cost	153,781	159,180
Computer software
Property, Plant and Equipment [Line Items]
Property and equipment, cost	244,649	250,585
Furniture and equipment
Property, Plant and Equipment [Line Items]
Property and equipment, cost	91,358	91,112
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, cost	$ 163,201	$ 164,807