Annual report [Section 13 and 15(d), not S-K Item 405]

INVESTMENTS - Schedule of Fair Value Measurement Inputs and Valuation Techniques (Details)

v3.25.3
INVESTMENTS - Schedule of Fair Value Measurement Inputs and Valuation Techniques (Details)
$ in Thousands
Sep. 30, 2025
USD ($)
investment
Sep. 30, 2024
USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value $ 859,124 [1] $ 796,260 [2]
Investments at fair value 859,124 796,260
Gladstone Alternative Income Fund    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 5,100  
Leeds Acquisition Holdings, LLC    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 36 38
Secured first lien debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 622,371 554,937
Secured second lien debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 150,542 113,716
Unsecured debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 333 32
Significant Unobservable Inputs (Level 3)    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value 854,013 796,222
Investments at fair value 854,013 796,222
Significant Unobservable Inputs (Level 3) | Secured first lien debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 622,371 554,937
Significant Unobservable Inputs (Level 3) | Secured second lien debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 150,542 113,716
Significant Unobservable Inputs (Level 3) | Unsecured debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 333 32
Significant Unobservable Inputs (Level 3) | Expected Payoff Amount | Preferred and common equity / equivalents    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value $ 2,200  
Investment owned, number of investments | investment 1  
Significant Unobservable Inputs (Level 3) | Yield Analysis | Secured first lien debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value $ 548,670 464,090
Significant Unobservable Inputs (Level 3) | Yield Analysis | Secured second lien debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value $ 141,750 $ 101,928
Significant Unobservable Inputs (Level 3) | Yield Analysis | Discount Rate | Secured first lien debt | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 0.094 0.108
Significant Unobservable Inputs (Level 3) | Yield Analysis | Discount Rate | Secured first lien debt | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 0.198 0.173
Significant Unobservable Inputs (Level 3) | Yield Analysis | Discount Rate | Secured first lien debt | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 0.117 0.126
Significant Unobservable Inputs (Level 3) | Yield Analysis | Discount Rate | Secured second lien debt | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 0.114 0.122
Significant Unobservable Inputs (Level 3) | Yield Analysis | Discount Rate | Secured second lien debt | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 0.152 0.160
Significant Unobservable Inputs (Level 3) | Yield Analysis | Discount Rate | Secured second lien debt | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 0.131 0.141
Significant Unobservable Inputs (Level 3) | TEV | Secured first lien debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value $ 73,701 $ 90,847
Significant Unobservable Inputs (Level 3) | TEV | Secured second lien debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value 8,792 8,547
Significant Unobservable Inputs (Level 3) | TEV | Unsecured debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value 333 32
Significant Unobservable Inputs (Level 3) | TEV | Preferred and common equity / equivalents    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value $ 80,767 $ 127,537
Significant Unobservable Inputs (Level 3) | TEV | EBITDA multiple | Secured first lien debt | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 3.5 4.1
Significant Unobservable Inputs (Level 3) | TEV | EBITDA multiple | Secured first lien debt | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 8.0 13.9
Significant Unobservable Inputs (Level 3) | TEV | EBITDA multiple | Secured first lien debt | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 6.0 10.0
Significant Unobservable Inputs (Level 3) | TEV | EBITDA multiple | Secured second lien debt | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 5.4 5.4
Significant Unobservable Inputs (Level 3) | TEV | EBITDA multiple | Secured second lien debt | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 5.4 5.4
Significant Unobservable Inputs (Level 3) | TEV | EBITDA multiple | Secured second lien debt | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 5.4 5.4
Significant Unobservable Inputs (Level 3) | TEV | EBITDA multiple | Unsecured debt | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 8.0 0.0
Significant Unobservable Inputs (Level 3) | TEV | EBITDA multiple | Unsecured debt | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 8.0 0.0
Significant Unobservable Inputs (Level 3) | TEV | EBITDA multiple | Unsecured debt | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 8.0 0.0
Significant Unobservable Inputs (Level 3) | TEV | EBITDA multiple | Preferred and common equity / equivalents | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 3.5 4.1
Significant Unobservable Inputs (Level 3) | TEV | EBITDA multiple | Preferred and common equity / equivalents | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 14.6 13.9
Significant Unobservable Inputs (Level 3) | TEV | EBITDA multiple | Preferred and common equity / equivalents | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 6.8 8.0
Significant Unobservable Inputs (Level 3) | TEV | EBITDA | Secured first lien debt | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value $ 538 $ 3,020
Significant Unobservable Inputs (Level 3) | TEV | EBITDA | Secured first lien debt | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value 4,655 16,211
Significant Unobservable Inputs (Level 3) | TEV | EBITDA | Secured first lien debt | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value 3,540 10,309
Significant Unobservable Inputs (Level 3) | TEV | EBITDA | Secured second lien debt | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value 2,345 3,343
Significant Unobservable Inputs (Level 3) | TEV | EBITDA | Secured second lien debt | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value 2,345 3,343
Significant Unobservable Inputs (Level 3) | TEV | EBITDA | Secured second lien debt | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value 2,345 3,343
Significant Unobservable Inputs (Level 3) | TEV | EBITDA | Unsecured debt | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value 3,804 0
Significant Unobservable Inputs (Level 3) | TEV | EBITDA | Unsecured debt | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value 3,804 0
Significant Unobservable Inputs (Level 3) | TEV | EBITDA | Unsecured debt | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value 3,804 0
Significant Unobservable Inputs (Level 3) | TEV | EBITDA | Preferred and common equity / equivalents | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value 538 1,182
Significant Unobservable Inputs (Level 3) | TEV | EBITDA | Preferred and common equity / equivalents | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value 142,549 144,458
Significant Unobservable Inputs (Level 3) | TEV | EBITDA | Preferred and common equity / equivalents | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value $ 10,222 $ 10,847
Significant Unobservable Inputs (Level 3) | TEV | Revenue multiple | Secured first lien debt | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 0.6 0.2
Significant Unobservable Inputs (Level 3) | TEV | Revenue multiple | Secured first lien debt | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 0.8 4.6
Significant Unobservable Inputs (Level 3) | TEV | Revenue multiple | Secured first lien debt | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 0.7 2.1
Significant Unobservable Inputs (Level 3) | TEV | Revenue multiple | Unsecured debt | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 0.9 1.0
Significant Unobservable Inputs (Level 3) | TEV | Revenue multiple | Unsecured debt | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 0.9 1.0
Significant Unobservable Inputs (Level 3) | TEV | Revenue multiple | Unsecured debt | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 0.9 1.0
Significant Unobservable Inputs (Level 3) | TEV | Revenue multiple | Preferred and common equity / equivalents | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 0.6 0.2
Significant Unobservable Inputs (Level 3) | TEV | Revenue multiple | Preferred and common equity / equivalents | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 0.9 4.6
Significant Unobservable Inputs (Level 3) | TEV | Revenue multiple | Preferred and common equity / equivalents | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input 0.7 2.0
Significant Unobservable Inputs (Level 3) | TEV | Revenue | Secured first lien debt | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value $ 10,844 $ 6,336
Significant Unobservable Inputs (Level 3) | TEV | Revenue | Secured first lien debt | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value 21,649 21,118
Significant Unobservable Inputs (Level 3) | TEV | Revenue | Secured first lien debt | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value 15,090 13,981
Significant Unobservable Inputs (Level 3) | TEV | Revenue | Unsecured debt | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value 4,846 7,834
Significant Unobservable Inputs (Level 3) | TEV | Revenue | Unsecured debt | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value 4,846 7,834
Significant Unobservable Inputs (Level 3) | TEV | Revenue | Unsecured debt | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value 4,846 7,834
Significant Unobservable Inputs (Level 3) | TEV | Revenue | Preferred and common equity / equivalents | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value 4,846 4,672
Significant Unobservable Inputs (Level 3) | TEV | Revenue | Preferred and common equity / equivalents | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value 21,649 21,118
Significant Unobservable Inputs (Level 3) | TEV | Revenue | Preferred and common equity / equivalents | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value 12,394 12,587
Significant Unobservable Inputs (Level 3) | Market Quote | Secured second lien debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments owned, fair value $ 0 $ 3,241
Significant Unobservable Inputs (Level 3) | Market Quote | IBP | Secured second lien debt | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input   0.880
Significant Unobservable Inputs (Level 3) | Market Quote | IBP | Secured second lien debt | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input   0.880
Significant Unobservable Inputs (Level 3) | Market Quote | IBP | Secured second lien debt | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investment owned, measurement input   0.880
[1] Cumulative gross unrealized depreciation for federal income tax purposes is $59.7 million; cumulative gross unrealized appreciation for federal income tax purposes is $34.1 million. Cumulative net unrealized depreciation is $25.5 million, based on a tax cost of $884.7 million.
[2] Cumulative gross unrealized depreciation for federal income tax purposes is $66.1 million; cumulative gross unrealized appreciation for federal income tax purposes is $85.8 million. Cumulative net unrealized appreciation is $19.7 million, based on a tax cost of $776.5 million