Business and Significant Accounting Policies - Property, Equipment and Leasehold Improvements, Less Accumulated Depreciation and Amortization (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property, equipment and leasehold improvements, gross	$ 654,887	$ 676,368
Less — accumulated depreciation and amortization	(381,325)	(339,603)
Property, equipment and leasehold improvements, net	273,562	336,765
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property, equipment and leasehold improvements, gross	$ 304,386	277,973
Computer equipment and software | Minimum
Property, Plant and Equipment [Line Items]
Useful Life	2 years
Computer equipment and software | Maximum
Property, Plant and Equipment [Line Items]
Useful Life	7 years
Furniture and equipment
Property, Plant and Equipment [Line Items]
Property, equipment and leasehold improvements, gross	$ 97,050	114,622
Furniture and equipment | Minimum
Property, Plant and Equipment [Line Items]
Useful Life	3 years
Furniture and equipment | Maximum
Property, Plant and Equipment [Line Items]
Useful Life	8 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, equipment and leasehold improvements, gross	$ 253,451	$ 283,773
Leasehold improvements | Minimum
Property, Plant and Equipment [Line Items]
Useful Life	2 years
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Useful Life	15 years