Fair Value Measurements - Balance Sheet Grouping (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	$ 91.8	$ 91.3
Unfunded Commitments	129.9	130.6
Fair Value Using NAV	21.7	22.5
Unfunded Commitments	0.0	0.0
Unfunded Commitments	221.7	221.9
Mezzanine Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	41.9	40.8
Unfunded Commitments	66.2	67.0
Real Estate Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	0.0	0.0
Senior Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	47.6	48.2
Unfunded Commitments	7.7	8.4
Leveraged Buyout
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	0.6	0.6
Unfunded Commitments	31.3	30.4
Secondary Transactions
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	1.6	1.6
Unfunded Commitments	1.6	1.6
Distressed Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	0.0	0.0
Unfunded Commitments	15.7	15.0
Equity Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	7.2	8.0
Hedge Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	0.0	0.0
Other Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	0.1	0.1
Unfunded Commitments	0.2	0.2
Measured at Net Asset Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	185.1	186.3
Fair Value Using NAV	196.6	183.6
Fair Value Using NAV	1.8	1.8
Fair Value Using NAV	383.5	371.7
Measured at Net Asset Value | Mezzanine Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	115.1	116.7
Fair Value Using NAV	118.4	116.9
Measured at Net Asset Value | Real Estate Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	27.4	27.3
Measured at Net Asset Value | Senior Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	21.2	19.1
Fair Value Using NAV	26.3	26.3
Measured at Net Asset Value | Leveraged Buyout
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	7.4	7.5
Fair Value Using NAV	30.8	19.2
Measured at Net Asset Value | Secondary Transactions
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	5.1	5.5
Fair Value Using NAV	2.2	2.4
Measured at Net Asset Value | Distressed Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	3.6	4.4
Fair Value Using NAV	11.1	11.7
Measured at Net Asset Value | Equity Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	7.7	7.0
Measured at Net Asset Value | Hedge Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	0.1	0.1
Measured at Net Asset Value | Other Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	5.2	5.7
Fair Value Using NAV	$ 0.1	$ 0.1