Quarterly report [Sections 13 or 15(d)]

RELATED PARTY TRANSACTIONS - Narrative (Details)

v3.26.1
RELATED PARTY TRANSACTIONS - Narrative (Details) - USD ($)
3 Months Ended 6 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2026
Mar. 31, 2025
Sep. 30, 2025
Related Party Transaction [Line Items]          
Base management fee 1.75% 1.75% 1.75%    
Base management fee, percent fee     100.00%    
Management and service fee, net of credit   0.50%   0.50%  
Management and service fees, loans     1.50%    
Ratio of net investment income (loss) to average net assets – annualized     6.71% 5.65%  
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%   20.00%    
Capital gains-based incentive fee $ 0   $ 0    
Investment company, net investment income to common stockholder distributions ratio, threshold   100.00%   100.00%  
Investment company, other operating expenses, due to advisor $ 200,000   $ 200,000   $ 100,000
Gladstone Securities          
Related Party Transaction [Line Items]          
Selling commissions, percentage 7.00%   7.00%    
Dealer manager fees percentage 3.00%   3.00%    
Payments for selling commissions and dealer-manager fees $ 800,000 $ 200,000 $ 1,900,000 $ 400,000  
Related Party          
Related Party Transaction [Line Items]          
Success fee income 100,000 $ 200,000 300,000 $ 400,000  
Fees due to related party 5,081,000   5,081,000   3,531,000
Related Party | Gladstone Investment Corporation          
Related Party Transaction [Line Items]          
Fees due to related party $ 66,000   $ 66,000   $ 52,000
Total fees due to Adviser | Chief Executive Officer | Related Party          
Related Party Transaction [Line Items]          
Noncontrolling interest, ownership percentage by parent 100.00%   100.00%    
Fee due to Administrator | Chief Executive Officer | Related Party          
Related Party Transaction [Line Items]          
Noncontrolling interest, ownership percentage by parent 100.00%   100.00%    
Gladstone Securities, LLC | Chief Executive Officer | Related Party          
Related Party Transaction [Line Items]          
Noncontrolling interest, ownership percentage by parent 100.00%   100.00%    
Maximum          
Related Party Transaction [Line Items]          
Base management fee     1.75%    
Minimum          
Related Party Transaction [Line Items]          
Ratio of net investment income (loss) to average net assets – annualized     1.75%