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

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

v3.25.1
INVESTMENTS - Fair Value Measurement Inputs and Valuation Techniques (Details)
$ in Thousands
Mar. 31, 2025
USD ($)
Mar. 31, 2024
USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 979,320 [1] $ 920,504 [2]
Investments at fair value 979,320 920,504
Secured First Lien Debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 514,334 474,856
Secured Second Lien Debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 103,580 138,703
Preferred Equity    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 302,163 213,480
Common Equity/ Equivalents    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 54,268 93,465
Common Equity/ Equivalents | Gladstone Alternative Income Fund ("GALT")    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 5,000  
Significant Unobservable Inputs (Level 3)    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 974,345 920,486
Investments at fair value 974,345 920,486
Significant Unobservable Inputs (Level 3) | Secured First Lien Debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 514,334 474,856
Significant Unobservable Inputs (Level 3) | Secured Second Lien Debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 103,580 138,703
Significant Unobservable Inputs (Level 3) | Preferred Equity    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 302,163 213,480
Significant Unobservable Inputs (Level 3) | Common Equity/ Equivalents    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 54,268 93,447
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | Secured First Lien Debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 514,334 474,856
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | Secured Second Lien Debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 90,956 113,703
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | Preferred Equity    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 302,163 213,480
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | Common Equity/ Equivalents    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 54,268 $ 93,447
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA multiple | Secured First Lien Debt | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value, measurement input 3.7 4.2
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA multiple | Secured First Lien Debt | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value, measurement input 7.9 8.8
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA multiple | Secured First Lien Debt | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value, measurement input 6.0 6.4
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA multiple | Secured Second Lien Debt | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value, measurement input 6.1 5.1
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA multiple | Secured Second Lien Debt | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value, measurement input 7.2 15.0
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA multiple | Secured Second Lien Debt | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value, measurement input 6.8 7.0
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA multiple | Preferred Equity | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value, measurement input 3.7 4.2
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA multiple | Preferred Equity | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value, measurement input 7.9 8.8
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA multiple | Preferred Equity | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value, measurement input 6.1 6.1
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA multiple | Common Equity/ Equivalents | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value, measurement input 5.5 5.0
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA multiple | Common Equity/ Equivalents | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value, measurement input 7.2 15.0
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA multiple | Common Equity/ Equivalents | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value, measurement input 6.8 6.4
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA | Secured First Lien Debt | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 1,208 $ 1,091
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA | Secured First Lien Debt | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 25,038 23,547
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA | Secured First Lien Debt | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 12,162 10,509
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA | Secured Second Lien Debt | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 3,637 5,648
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA | Secured Second Lien Debt | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 24,234 23,003
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA | Secured Second Lien Debt | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 16,900 14,192
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA | Preferred Equity | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 2,153 1,091
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA | Preferred Equity | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 25,038 23,547
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA | Preferred Equity | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 11,029 9,502
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA | Common Equity/ Equivalents | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 1,208 1,154
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA | Common Equity/ Equivalents | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 24,234 63,269
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | EBITDA | Common Equity/ Equivalents | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 18,562 $ 23,615
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | Revenue multiple | Secured First Lien Debt | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value, measurement input 0.3 0.3
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | Revenue multiple | Secured First Lien Debt | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value, measurement input 0.6 0.6
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | Revenue multiple | Secured First Lien Debt | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value, measurement input 0.4 0.4
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | Revenue multiple | Preferred Equity | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value, measurement input 0.3 0.3
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | Revenue multiple | Preferred Equity | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value, measurement input 0.6 0.6
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | Revenue multiple | Preferred Equity | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value, measurement input 0.4 0.4
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | Revenue | Secured First Lien Debt | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 6,690 $ 31,586
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | Revenue | Secured First Lien Debt | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 102,791 93,916
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | Revenue | Secured First Lien Debt | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 72,303 77,580
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | Revenue | Preferred Equity | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 6,690 31,586
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | Revenue | Preferred Equity | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 102,791 93,916
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | Revenue | Preferred Equity | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 53,604 75,099
Significant Unobservable Inputs (Level 3) | Yield Analysis | Secured Second Lien Debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 12,624 $ 25,000
Significant Unobservable Inputs (Level 3) | Yield Analysis | Discount Rate | Secured Second Lien Debt | Minimum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value, measurement input 0.207 0.138
Significant Unobservable Inputs (Level 3) | Yield Analysis | Discount Rate | Secured Second Lien Debt | Maximum    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value, measurement input 0.207 0.138
Significant Unobservable Inputs (Level 3) | Yield Analysis | Discount Rate | Secured Second Lien Debt | Weighted Average    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value, measurement input 0.207 0.138
Significant Other Observable Inputs (Level 2)    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value $ 0 $ 18
Significant Other Observable Inputs (Level 2) | Secured First Lien Debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 0 0
Significant Other Observable Inputs (Level 2) | Secured Second Lien Debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 0 0
Significant Other Observable Inputs (Level 2) | Preferred Equity    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 0 0
Significant Other Observable Inputs (Level 2) | Common Equity/ Equivalents    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value $ 0 18
Significant Other Observable Inputs (Level 2) | Common Equity/ Equivalents | Funko Acquisition Holdings, LLC    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value   $ 18
[1] Cumulative gross unrealized appreciation for federal income tax purposes is $183.3 million; cumulative gross unrealized depreciation for federal income tax purposes is $144.9 million. Cumulative net unrealized appreciation is $38.5 million, based on a tax cost of $940.9 million.
[2] Cumulative gross unrealized appreciation for federal income tax purposes is $180.5 million; cumulative gross unrealized depreciation for federal income tax purposes is $115.8 million. Cumulative net unrealized appreciation is $64.7 million, based on a tax cost of $855.8 million.