Quarterly report pursuant to Section 13 or 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
Mar. 31, 2024
Dec. 31, 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value: $ 4,548,027 [1] $ 4,286,271 [2]
Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value: 4,548,027 4,286,271
Fair Value, Recurring | LMM portfolio investments    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value: 2,361,511 2,273,000
Fair Value, Recurring | Private Loan portfolio investments    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value: 1,519,538 1,453,549
Fair Value, Recurring | Middle Market portfolio investments    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value: 238,553 243,695
Fair Value, Recurring | Other Portfolio investments    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value: 139,782 141,964
Fair Value, Recurring | External Investment Manager    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value: 185,260 174,063
Fair Value, Recurring | Short-term portfolio investments    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value: 103,383  
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) | Fair Value, Recurring | LMM portfolio investments    
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) | Fair Value, Recurring | Private Loan portfolio investments    
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) | Fair Value, Recurring | Middle Market portfolio investments    
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) | Fair Value, Recurring | Other Portfolio investments    
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) | Fair Value, Recurring | External Investment Manager    
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) | Fair Value, Recurring | Short-term portfolio investments    
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: 103,383 0
Significant Other Observable Inputs (Level 2) | Fair Value, Recurring | LMM portfolio investments    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value: 0 0
Significant Other Observable Inputs (Level 2) | Fair Value, Recurring | Private Loan portfolio investments    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value: 0 0
Significant Other Observable Inputs (Level 2) | Fair Value, Recurring | Middle Market portfolio investments    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value: 0 0
Significant Other Observable Inputs (Level 2) | Fair Value, Recurring | Other Portfolio investments    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value: 0 0
Significant Other Observable Inputs (Level 2) | Fair Value, Recurring | External Investment Manager    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value: 0 0
Significant Other Observable Inputs (Level 2) | Fair Value, Recurring | Short-term portfolio investments    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value: 103,383  
Significant Unobservable Inputs (Level 3)    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value: 4,444,644 4,286,271
Significant Unobservable Inputs (Level 3) | Fair Value, Recurring    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value: 4,444,644 4,286,271
Significant Unobservable Inputs (Level 3) | Fair Value, Recurring | LMM portfolio investments    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value: 2,361,511 2,273,000
Significant Unobservable Inputs (Level 3) | Fair Value, Recurring | Private Loan portfolio investments    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value: 1,519,538 1,453,549
Significant Unobservable Inputs (Level 3) | Fair Value, Recurring | Middle Market portfolio investments    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value: 238,553 243,695
Significant Unobservable Inputs (Level 3) | Fair Value, Recurring | Other Portfolio investments    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value: 139,782 141,964
Significant Unobservable Inputs (Level 3) | Fair Value, Recurring | External Investment Manager    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments at fair value: 185,260 $ 174,063
Significant Unobservable Inputs (Level 3) | Fair Value, Recurring | Short-term portfolio investments    
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.