Annual report pursuant to Section 13 and 15(d)

FAIR VALUE HIERARCHY FOR INVESTMENTS???PORTFOLIO COMPOSITION - Schedule of Fair Value Hierarchy (Details)

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FAIR VALUE HIERARCHY FOR INVESTMENTS—PORTFOLIO COMPOSITION - Schedule of Fair Value Hierarchy (Details) - USD ($)
$ in Thousands
Dec. 31, 2023
Dec. 31, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value $ 4,286,271 [1] $ 4,102,177 [2]
Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 4,286,271 4,102,177
LMM portfolio investments | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 2,273,000 2,060,459
Private Loan portfolio investments | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 1,453,549 1,471,466
Middle Market portfolio investments | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 243,695 329,119
Other Portfolio investments | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 141,964 116,299
External Investment Manager | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 174,063 122,930
Short-term portfolio investments | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value   1,904
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 0 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | LMM portfolio investments | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 0 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Private Loan portfolio investments | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 0 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Middle Market portfolio investments | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 0 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Portfolio investments | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 0 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | External Investment Manager | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 0 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term portfolio investments | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value   0
Significant Other Observable Inputs (Level 2) | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 0 1,904
Significant Other Observable Inputs (Level 2) | LMM portfolio investments | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 0 0
Significant Other Observable Inputs (Level 2) | Private Loan portfolio investments | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 0 0
Significant Other Observable Inputs (Level 2) | Middle Market portfolio investments | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 0 0
Significant Other Observable Inputs (Level 2) | Other Portfolio investments | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 0 0
Significant Other Observable Inputs (Level 2) | External Investment Manager | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 0 0
Significant Other Observable Inputs (Level 2) | Short-term portfolio investments | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value   1,904
Significant Unobservable Inputs (Level 3)    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 4,286,271 4,100,273
Significant Unobservable Inputs (Level 3) | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 4,286,271 4,100,273
Significant Unobservable Inputs (Level 3) | LMM portfolio investments | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 2,273,000 2,060,459
Significant Unobservable Inputs (Level 3) | Private Loan portfolio investments | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 1,453,549 1,471,466
Significant Unobservable Inputs (Level 3) | Middle Market portfolio investments | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 243,695 329,119
Significant Unobservable Inputs (Level 3) | Other Portfolio investments | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value 141,964 116,299
Significant Unobservable Inputs (Level 3) | External Investment Manager | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value $ 174,063 122,930
Significant Unobservable Inputs (Level 3) | Short-term portfolio investments | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value   $ 0
[1] Investment fair value was determined using significant unobservable inputs, unless otherwise noted. See Note C — Fair Value Hierarchy for Investments — Portfolio Composition for further discussion. Negative fair value is the result of the capitalized discount on the loan or the unfunded commitment being valued below par.
[2] Investment fair value was determined using significant unobservable inputs, unless otherwise noted. See Note C — Fair Value Hierarchy for Investments — Portfolio Composition for further discussion. Negative fair value is the result of the capitalized discount on the loan or the unfunded commitment being valued below par.