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INVESTMENTS - Fair Value, Assets Measured on Recurring Basis (Details) - USD ($) $ in Thousands | Dec. 31, 2023 | Sep. 30, 2023
--- | --- | ---
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | $ 749,739 | $ 704,584
Leeds Acquisition Holdings L L C |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 200 | 200
Funko Acquisition Holdings, LLC |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 22,000 | 22
Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 0 | 0
Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 22 | 22
Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 749,717 | 704,562
Significant Unobservable Inputs (Level 3) | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 749,717 | 704,562
Significant Unobservable Inputs (Level 3) | Non-Control/Non-Affiliate investments | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 708,238 | 663,291
Significant Unobservable Inputs (Level 3) | Affiliate investments | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 10,716 | 10,421
Significant Unobservable Inputs (Level 3) | Control investments | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 30,763 | 30,850
Secured first lien debt |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 546,602 | 510,701
Secured first lien debt | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 0 | 0
Secured first lien debt | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 0 | 0
Secured first lien debt | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 546,602 | 510,701
Secured first lien debt | Significant Unobservable Inputs (Level 3) | Non-Control/Non-Affiliate investments | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 529,003 | 491,686
Secured first lien debt | Significant Unobservable Inputs (Level 3) | Affiliate investments | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 2,829 | 2,895
Secured first lien debt | Significant Unobservable Inputs (Level 3) | Control investments | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 14,770 | 16,120
Secured second lien debt |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 126,571 | 127,854
Secured second lien debt | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 0 | 0
Secured second lien debt | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 0 | 0
Secured second lien debt | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 126,571 | 127,854
Secured second lien debt | Significant Unobservable Inputs (Level 3) | Non-Control/Non-Affiliate investments | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 119,146 | 120,429
Secured second lien debt | Significant Unobservable Inputs (Level 3) | Control investments | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 7,425 | 7,425
Unsecured debt |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 23 | 24
Unsecured debt | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 0 | 0
Unsecured debt | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 0 | 0
Unsecured debt | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 23 | 24
Unsecured debt | Significant Unobservable Inputs (Level 3) | Non-Control/Non-Affiliate investments | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 23 | 24
Preferred equity |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 29,722 | 26,855
Preferred equity | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 0 | 0
Preferred equity | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 0 | 0
Preferred equity | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 29,722 | 26,855
Preferred equity | Significant Unobservable Inputs (Level 3) | Non-Control/Non-Affiliate investments | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 24,589 | 21,733
Preferred equity | Significant Unobservable Inputs (Level 3) | Affiliate investments | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 5,133 | 5,122
Common equity/equivalents |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 46,821 | 39,150
Common equity/equivalents | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 0 | 0
Common equity/equivalents | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 22 | 22
Common equity/equivalents | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 46,799 | 39,128
Common equity/equivalents | Significant Unobservable Inputs (Level 3) | Non-Control/Non-Affiliate investments | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 35,477 | 29,419
Common equity/equivalents | Significant Unobservable Inputs (Level 3) | Affiliate investments | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 2,754 | 2,404
Common equity/equivalents | Significant Unobservable Inputs (Level 3) | Control investments | Fair Value, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | $ 8,568 | $ 7,305

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