Quarterly report pursuant to Section 13 or 15(d)

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

v3.25.0.1
INVESTMENTS - Schedule of Fair Value Measurement Inputs and Valuation Techniques (Details)
$ in Thousands
Dec. 31, 2024
USD ($)
Mar. 31, 2024
USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 1,072,230 $ 920,504 [1]
Investments at fair value 1,067,230 920,504
Secured First Lien Debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 599,911 474,856
Secured Second Lien Debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 108,743 138,703
Preferred Equity    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 308,226 213,480
Common Equity/ Equivalents    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 50,350 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 1,067,230 920,486
Investments at fair value 1,067,230 920,486
Significant Unobservable Inputs (Level 3) | Secured First Lien Debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 599,911 474,856
Significant Unobservable Inputs (Level 3) | Secured Second Lien Debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 108,743 138,703
Significant Unobservable Inputs (Level 3) | Preferred Equity    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 308,226 213,480
Significant Unobservable Inputs (Level 3) | Common Equity/ Equivalents    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Investments at fair value 50,350 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 599,911 474,856
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | Secured Second Lien Debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 96,229 113,703
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | Preferred Equity    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value 308,226 213,480
Significant Unobservable Inputs (Level 3) | Total Enterprise Value | Common Equity/ Equivalents    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 50,350 $ 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 2.8 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 11.8 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 6.8 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 5.7 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 7.0 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 6.6 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 2.8 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 11.8 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 6.0 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 8.1 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 6.6 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 $ 969 $ 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 26,000 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 12,328 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 4,489 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 23,258 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 14,721 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 1,292 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 26,000 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 11,696 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 969 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 23,258 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 $ 17,987 $ 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 0.2 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 0.2 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 0.3 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 $ 6,141 $ 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 100,934 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 70,883 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 6,141 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 100,934 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 52,338 75,099
Significant Unobservable Inputs (Level 3) | Yield Analysis | Secured Second Lien Debt    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair Value $ 12,514 $ 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 0.197 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 0.197 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 0.197 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 $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.