Fixed Assets, Net - Components of Fixed Assets, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Property, Plant and Equipment
Total, cost	$ 360,884	$ 339,838
Accumulated depreciation and amortization	(187,611)	(161,803)
Total, net	173,273	178,035
Leasehold improvements, furniture and fixtures, and other fixed assets
Property, Plant and Equipment
Total, cost	258,089	245,262
Software, including software development costs
Property, Plant and Equipment
Total, cost	62,673	56,883
Computer and communications equipment
Property, Plant and Equipment
Total, cost	$ 40,122	$ 37,693