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Fair Value of Financial Instruments (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Total investments at fair value $ 2,180.6 $ 2,502.4
Total investments at fair value, estimated fair value 2,180.6 2,502.4
Cash and cash equivalents 226.4 89.2
Cash and cash equivalents, estimated fair value 226.4 89.2
Restricted cash and cash equivalents $ 0.2 0.2
Fair value investments entities that calculate net asset value per share liquidating investment original expected lives increments 1 year  
Unfunded commitment, private investment fund $ 25.4 55.2
Minimum [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Liquidating Investment, Remaining Period 3 years  
Maximum [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Liquidating Investment, Remaining Period 12 years  
Estimate of Fair Value Measurement [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Restricted cash and cash equivalents $ 0.2 $ 0.2