Quarterly report pursuant to Section 13 or 15(d)

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)

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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)
$ in Millions
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2024
USD ($)
company
Sep. 30, 2023
company
Sep. 30, 2024
USD ($)
Sep. 30, 2023
Sep. 30, 2024
USD ($)
company
Dec. 31, 2023
USD ($)
Schedule of Investments [Line Items]            
Cash equivalents | $ $ 35.4   $ 35.4   $ 35.4 $ 15.2
Cash exceeded federal deposit insurance corporation insurance protection levels | $ $ 44.7   $ 44.7   $ 44.7 $ 40.1
Percentage of total investment income, attributable to noncash paid-in-kind interest income (as a percent) 4.40% 1.90% 3.80% 2.00%    
Percentage of total investment come, attributable to noncash cumulative dividend income (as a percent) 0.50% 0.30% 0.40% 0.30%    
Percentage of total investment income, attributable to interest income, debt investments, net (as a percent) 2.20% 1.90% 2.00% 1.80%    
Investment Owned, At Fair Value | Investment Type Concentration Risk            
Schedule of Investments [Line Items]            
Concentration risk (as a percent)     100.00%     100.00%
Investment Owned, At Cost | Investment Type Concentration Risk            
Schedule of Investments [Line Items]            
Concentration risk (as a percent)     100.00%     100.00%
Non-accrual Status | Investment Owned, At Fair Value | Investment Type Concentration Risk            
Schedule of Investments [Line Items]            
Concentration risk (as a percent)     1.40%     0.60%
Non-accrual Status | Investment Owned, At Cost | Investment Type Concentration Risk            
Schedule of Investments [Line Items]            
Concentration risk (as a percent)     3.90%     2.30%
Revolving Credit Facility | Line of Credit            
Schedule of Investments [Line Items]            
Commitment fee (as a percentage)     3.40%      
LMM portfolio investments            
Schedule of Investments [Line Items]            
Consultation period subsequent to initial investment (in months)     12 months      
Investment company, number of portfolio companies with annual third-party appraisal was obtained, reviewed and certified | company 16 16     68  
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 (as a percent) 24.00% 22.00%     94.00%  
Private Loan portfolio investments            
Schedule of Investments [Line Items]            
Consultation period subsequent to initial investment (in months)     12 months      
Investment company, number of portfolio companies with annual third-party appraisal was obtained, reviewed and certified | company 17 15     61  
Percentage of portfolio with annual third-party appraisal was obtained, reviewed and certified (as a percent)         97.00%  
Private Loan portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk            
Schedule of Investments [Line Items]            
Concentration risk (as a percent) 24.00% 25.00%     72.00%  
Middle Market portfolio investments            
Schedule of Investments [Line Items]            
Percentage of portfolio investments containing limited consultation with financial advisory services firm (as a percent) 97.00%   97.00%   97.00% 98.00%
Other Portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk            
Schedule of Investments [Line Items]            
Concentration risk (as a percent)     3.30%     3.30%
Other Portfolio investments | Investment Owned, At Cost | Investment Type Concentration Risk            
Schedule of Investments [Line Items]            
Concentration risk (as a percent)     3.70%     4.00%