Fixed Assets - Schedule of Components of Fixed Assets (Details) - Consolidated Entity Excluding Consolidated Funds - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Property, Plant and Equipment [Line Items]
Fixed assets, at cost	$ 162.3	$ 154.6
Accumulated depreciation and amortization	(131.3)	(118.9)
Fixed assets, net	31.0	35.7
Leasehold improvements
Property, Plant and Equipment [Line Items]
Fixed assets, at cost	28.8	28.5
Office equipment
Property, Plant and Equipment [Line Items]
Fixed assets, at cost	9.3	8.7
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Fixed assets, at cost	6.4	6.3
Software and web development
Property, Plant and Equipment [Line Items]
Fixed assets, at cost	$ 117.8	$ 111.1