Quarterly report pursuant to Section 13 or 15(d)

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

v3.23.1
FAIR VALUE HIERARCHY FOR INVESTMENTS—PORTFOLIO COMPOSITION - Fair Value Hierarchy (Details) - USD ($)
$ in Thousands
Mar. 31, 2023
Dec. 31, 2022
Mar. 31, 2022
 [2]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Investments at fair value: $ 4,160,917 $ 4,102,177 [1] $ 4,160,917
Fair Value, Recurring      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Investments at fair value: 4,160,917 4,102,177  
Fair Value, Recurring | LMM portfolio investments      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Investments at fair value: 2,112,619 2,060,459  
Fair Value, Recurring | Private Loan portfolio investments      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Investments at fair value: 1,491,395 1,471,466  
Fair Value, Recurring | Middle Market portfolio investments      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Investments at fair value: 306,244 329,119  
Fair Value, Recurring | Other Portfolio investments      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Investments at fair value: 116,067 116,299  
Fair Value, Recurring | External Investment Manager investments      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Investments at fair value: 132,650 122,930  
Fair Value, Recurring | Short-term portfolio investments      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Investments at fair value: 1,942 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) | 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 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 | Short-term 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      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Investments at fair value: 1,942 1,904  
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 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 | Short-term portfolio investments      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Investments at fair value: 1,942 1,904  
Significant Unobservable Inputs (Level 3)      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Investments at fair value: 4,158,975 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: 4,158,975 4,100,273  
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: 2,112,619 2,060,459  
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: 1,491,395 1,471,466  
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: 306,244 329,119  
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: 116,067 116,299  
Significant Unobservable Inputs (Level 3) | Fair Value, Recurring | External Investment Manager investments      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Investments at fair value: 132,650 122,930  
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 $ 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.