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INVESTMENTS - Fair Value, Assets Measured on Recurring Basis (Details) - USD ($) $ in Thousands | Sep. 30, 2023 | Sep. 30, 2022
--- | --- | ---
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | $ 704,584 | $ 643,218
Leeds Acquisition Holdings, LLC |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 200 | 6,400
Funko Acquisition Holdings, LLC |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 22 | 58
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 | 58
Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 704,562 | 643,160
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 | 704,562 | 643,160
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 | 663,291 | 568,356
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 | 10,421 | 39,091
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 | 30,850 | 35,713
Secured first lien debt |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 510,701 | 463,858
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 | 510,701 | 463,858
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 | 491,686 | 413,631
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 | 2,895 | 34,804
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 | 16,120 | 15,423
Secured second lien debt |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 127,854 | 115,928
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 | 127,854 | 115,928
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 | 120,429 | 108,263
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 | 7,665
Unsecured debt |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 24 | 55
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 | 24 | 55
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 | 24 | 55
Preferred equity |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 26,855 | 27,046
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 | 26,855 | 27,046
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 | 21,733 | 17,719
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 | 5,122 | 3,640
Preferred equity | 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 | 0 | 5,687
Common equity/equivalents |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 39,150 | 36,331
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 | 58
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 | 39,128 | 36,273
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 | 29,419 | 28,688
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 | 2,404 | 647
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 | $ 7,305 | $ 6,938

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