Quarterly report [Sections 13 or 15(d)]

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)

v3.25.3
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)
$ in Millions
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2025
USD ($)
company
Sep. 30, 2024
company
Sep. 30, 2025
USD ($)
segment
Sep. 30, 2024
Sep. 30, 2025
USD ($)
company
Jun. 30, 2025
company
Dec. 31, 2024
USD ($)
Schedule of Investments [Line Items]              
Concentration risk, percentage (as a percent)     100.00%       100.00%
Cash equivalents | $ $ 12.3   $ 12.3   $ 12.3   $ 14.4
Cash balances exceeded federal deposit insurance corporation insurance protection levels | $ $ 4.8   $ 4.8   $ 4.8   $ 13.5
Percentage of total investment income, attributable to noncash paid-in-kind interest income (as a percent) 6.50% 6.70% 5.90% 5.40%      
Percentage of total investment income, attributable to noncash cumulative dividend income (as a percent) 0.90% 0.10% 0.90% 0.10%      
Percentage of total investment income, attributable to interest income, debt investments, net (as a percent) 2.40% 3.00% 2.40% 2.80%      
Number of reportable segments | segment     1        
Investment Owned, At Fair Value | Investment Type Concentration Risk              
Schedule of Investments [Line Items]              
Concentration risk, percentage (as a percent)     100.00%       100.00%
Investment Owned, At Fair Value | Investment Type Concentration Risk | Nonperforming Financial Instruments              
Schedule of Investments [Line Items]              
Concentration risk, percentage (as a percent)     1.40%       1.50%
Investment Owned, At Cost | Investment Type Concentration Risk              
Schedule of Investments [Line Items]              
Concentration risk, percentage (as a percent)     100.00%       100.00%
Investment Owned, At Cost | Investment Type Concentration Risk | Nonperforming Financial Instruments              
Schedule of Investments [Line Items]              
Concentration risk, percentage (as a percent)     4.60%       5.60%
Private Loan portfolio investments              
Schedule of Investments [Line Items]              
Consultation period subsequent to initial investment     12 months        
Investment company, number of portfolio companies with annual third-party appraisal was obtained, reviewed and certified | company 14 17       61  
Percentage of portfolio with annual third-party appraisal was obtained, reviewed and certified (as a percent)         96.00%    
Private Loan portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk              
Schedule of Investments [Line Items]              
Concentration risk, percentage (as a percent) 22.00% 24.00%     90.00%    
LMM portfolio investments              
Schedule of Investments [Line Items]              
Consultation period subsequent to initial investment     12 months        
Investment company, number of portfolio companies with annual third-party appraisal was obtained, reviewed and certified | company 12 12     50    
Percentage of portfolio with annual third-party appraisal was obtained, reviewed and certified (as a percent)         99.00%    
LMM portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk              
Schedule of Investments [Line Items]              
Concentration risk, percentage (as a percent) 24.00% 22.00%     99.00%    
Middle Market portfolio investments              
Schedule of Investments [Line Items]              
Percentage of portfolio investments containing limited consultation with financial advisory services firm (as a percent) 89.00%   89.00%   89.00%   93.00%
Middle Market portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk              
Schedule of Investments [Line Items]              
Concentration risk, percentage (as a percent)     2.10%       3.30%
Middle Market portfolio investments | Investment Owned, At Cost | Investment Type Concentration Risk              
Schedule of Investments [Line Items]              
Concentration risk, percentage (as a percent)     3.40%       5.80%
Other Portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk              
Schedule of Investments [Line Items]              
Concentration risk, percentage (as a percent)     1.30%       2.00%
Other Portfolio investments | Investment Owned, At Cost | Investment Type Concentration Risk              
Schedule of Investments [Line Items]              
Concentration risk, percentage (as a percent)     1.20%       1.60%