Quarterly report pursuant to Section 13 or 15(d)

Fair Value of Financial Instruments - Schedule of Investments Measured at Fair Value on Recurring Basis (Details)

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Fair Value of Financial Instruments - Schedule of Investments Measured at Fair Value on Recurring Basis (Details) - Recurring - USD ($)
$ in Thousands
Sep. 30, 2023
Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments $ 3,256,708 $ 2,960,062
Senior Secured Debt    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 3,021,950 2,741,388
Unsecured Debt    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 69,930 54,056
Preferred Stock    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 42,290 41,488
Common Stock    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 94,705 92,484
Warrants    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 27,833 30,646
Investment Funds & Vehicles measured at Net Asset Value    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 4,683 3,893
Total Investments, at fair value    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 3,261,391 2,963,955
Derivative Instruments    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 230  
Total Investments, at fair value including derivative instruments    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 3,261,621  
Escrow Receivables    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Other assets 748 875
Quoted Prices in Active Markets for Identical Assets (Level 1)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 55,056 66,027
Quoted Prices in Active Markets for Identical Assets (Level 1) | Common Stock    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 55,056 66,027
Significant Other Observable Inputs (Level 2)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 7,715 12,625
Significant Other Observable Inputs (Level 2) | Common Stock    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments   1,398
Significant Other Observable Inputs (Level 2) | Warrants    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 7,715 11,227
Significant Unobservable Inputs (Level 3)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 3,193,937 2,881,410
Significant Unobservable Inputs (Level 3) | Senior Secured Debt    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 3,021,950 2,741,388
Significant Unobservable Inputs (Level 3) | Unsecured Debt    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 69,930 54,056
Significant Unobservable Inputs (Level 3) | Preferred Stock    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 42,290 41,488
Significant Unobservable Inputs (Level 3) | Common Stock    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 39,649 25,059
Significant Unobservable Inputs (Level 3) | Warrants    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments 20,118 19,419
Significant Unobservable Inputs (Level 3) | Escrow Receivables    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Other assets $ 748 $ 875