Significant Accounting Policies - Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Significant Accounting Policies Line Items [Line Items]
Gross Carrying Amount	$ 274,628	$ 263,335
Accumulated Amortization / Depreciation	(210,806)	(192,354)
Net Carrying Amount	63,822	70,981
Internal-use software
Significant Accounting Policies Line Items [Line Items]
Gross Carrying Amount	163,408	155,984
Accumulated Amortization / Depreciation	(110,845)	(100,734)
Net Carrying Amount	52,563	55,250
Leasehold improvements
Significant Accounting Policies Line Items [Line Items]
Gross Carrying Amount	39,339	39,134
Accumulated Amortization / Depreciation	(32,182)	(26,236)
Net Carrying Amount	7,157	12,898
Furniture and equipment
Significant Accounting Policies Line Items [Line Items]
Gross Carrying Amount	71,881	68,217
Accumulated Amortization / Depreciation	(67,779)	(65,384)
Net Carrying Amount	$ 4,102	$ 2,833