Significant Accounting Policies - Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Significant Accounting Policies Line Items [Line Items]
Gross Carrying Amount	$ 247,375	$ 234,486
Accumulated Amortization / Depreciation	(172,289)	(154,029)
Net Carrying Amount	75,086	80,457
Internal-use software
Significant Accounting Policies Line Items [Line Items]
Gross Carrying Amount	145,248	136,033
Accumulated Amortization / Depreciation	(91,542)	(81,724)
Net Carrying Amount	53,706	54,309
Leasehold improvements
Significant Accounting Policies Line Items [Line Items]
Gross Carrying Amount	34,805	32,975
Accumulated Amortization / Depreciation	(18,108)	(15,608)
Net Carrying Amount	16,697	17,367
Furniture and equipment
Significant Accounting Policies Line Items [Line Items]
Gross Carrying Amount	67,322	65,478
Accumulated Amortization / Depreciation	(62,639)	(56,697)
Net Carrying Amount	$ 4,683	$ 8,781