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Fair Value Measurements - Balance Sheet Grouping (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	$ 22.2	$ 22.5
Unfunded Commitments	0.1	0.0
Reported Value Measurement
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	102.6	91.3
Unfunded Commitments	0.1	0.0
Unfunded Commitments	245.4	221.9
Mezzanine Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	36.2	40.8
Unfunded Commitments	69.8	67.0
Real Estate Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	0.1	0.0
Senior Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	64.1	48.2
Unfunded Commitments	6.7	8.4
Leveraged Buyout
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	0.6	0.6
Unfunded Commitments	42.7	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	5.8	8.0
Other Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	0.0	0.1
Unfunded Commitments	0.2	0.2
Real Estate
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded Commitments	0.2	0.0
Measured at Net Asset Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	1.8	1.8
Measured at Net Asset Value | Reported Value Measurement
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	174.9	186.3
Fair Value Using NAV	204.0	183.6
Unfunded Commitments	142.7	130.6
Fair Value Using NAV	1.8	1.8
Fair Value Using NAV	380.7	371.7
Measured at Net Asset Value | Mezzanine Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	115.2	116.7
Fair Value Using NAV	115.9	116.9
Measured at Net Asset Value | Real Estate Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	24.3	27.3
Measured at Net Asset Value | Senior Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	19.5	19.1
Fair Value Using NAV	26.5	26.3
Measured at Net Asset Value | Leveraged Buyout
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	6.5	7.5
Fair Value Using NAV	34.5	19.2
Measured at Net Asset Value | Secondary Transactions
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	2.7	5.5
Fair Value Using NAV	1.6	2.4
Measured at Net Asset Value | Distressed Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	1.4	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	10.4	7.0
Measured at Net Asset Value | Other Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	5.3	5.8
Fair Value Using NAV	3.9	0.1
Measured at Net Asset Value | Real Estate
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Using NAV	$ 0.1	$ 0.0

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