Borrowings - Outstanding Loans Payable of Consolidated Funds (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value of liabilities	$ 6,353.0	$ 6,298.6
Revolving credit facilities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Borrowing Outstanding	182.8	177.9
Fair Value	$ 182.8	$ 177.9
Weighted Average Interest Rate	6.57%	6.46%
Weighted Average Remaining Maturity in Years	4 years 8 months 26 days	5 years 18 days
Loans Payable of Consolidated Funds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Borrowing Outstanding	$ 6,536.3	$ 6,523.3
Fair Value	6,535.1	6,486.5
Senior secured notes
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Borrowing Outstanding	6,133.0	6,171.9
Fair Value	$ 6,153.0	$ 6,097.9
Weighted Average Interest Rate	6.36%	6.32%
Weighted Average Remaining Maturity in Years	8 years 10 months 2 days	8 years 11 months 26 days
Fair value of liabilities		$ 7.8
Subordinated notes
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Borrowing Outstanding	$ 220.5	173.5
Fair Value	$ 199.3	$ 210.7
Weighted Average Remaining Maturity in Years	8 years 11 months 8 days	9 years 1 month 28 days
Fair value of liabilities		$ 2.2