Quarterly report pursuant to Section 13 or 15(d)

RELATED PARTY TRANSACTIONS - Narrative (Details)

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RELATED PARTY TRANSACTIONS - Narrative (Details) - USD ($)
3 Months Ended 12 Months Ended
Jun. 30, 2024
Jun. 30, 2023
Mar. 31, 2024
Related Party Transaction [Line Items]      
Base management fee 2.00% 2.00%  
Base management fee, percent fee 100.00%    
Investment company, excess expense reimbursable $ 75,000 $ 75,000  
Maximum base management fee paid cannot exceed a percentage of total assets 2.00%    
Ratio of net investment income (loss) to average net assets – annualized 7.85% 4.55%  
Investment company, capital gains-based incentive fees $ 0   $ 1,100,000
Investment company, capital gains-based incentive fees payable (reversal) (3,800,000) $ 100,000  
Capital gains-based incentive fee 33,000,000.0   36,700,000
Administration fee [1] 506,000 522,000  
Success fee income 1,553,000 0  
Related Party      
Related Party Transaction [Line Items]      
Success fee income 0 $ 300,000  
Due from related parties 100,000   $ 100,000
Affiliated Entity | Advisory Agreement      
Related Party Transaction [Line Items]      
Incentive fee base on minimum rate of return required on investment $ 0    
Percentage of pre-incentive fee net investment income is less than the hurdle rate 100.00%    
Investment company, pre-incentive fee net investment income, percent threshold of net assets 2.1875%    
Pre-incentive fee net investment income exceeds the hurdle rate 20.00%    
Investment company, capital gains-based incentive fees 20.00%    
Affiliated Entity | Advisory Agreement | Minimum      
Related Party Transaction [Line Items]      
Ratio of net investment income (loss) to average net assets – annualized 1.75%    
Adviser | Chief Executive Officer | Related Party      
Related Party Transaction [Line Items]      
Ownership percentage by parent 100.00%    
Administrator | Chief Executive Officer | Related Party      
Related Party Transaction [Line Items]      
Ownership percentage by parent 100.00%    
Gladstone Securities, LLC | Chief Executive Officer | Related Party      
Related Party Transaction [Line Items]      
Ownership percentage by parent 100.00%    
[1] Refer to Note 4 — Related Party Transactions in the accompanying Notes to Consolidated Financial Statements for additional information.