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 12 Months Ended
Mar. 31, 2024
USD ($)
company
Mar. 31, 2023
company
Mar. 31, 2024
USD ($)
company
Dec. 31, 2023
USD ($)
Schedule of Investments [Line Items]        
Cash equivalents | $ $ 51.9   $ 51.9 $ 15.2
Cash exceeded federal deposit insurance corporation insurance protection levels | $ $ 58.0   $ 58.0 $ 40.1
Percentage of total investment income, attributable to noncash paid-in-kind interest income (as a percent) 3.20% 2.40%    
Percentage of total investment come, attributable to noncash cumulative dividend income (as a percent) 0.30% 0.30%    
Percentage of total investment income, attributable to interest income, debt investments, net (as a percent) 1.80% 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) 0.50%     0.60%
Non-accrual Status | Investment Owned, At Cost | Investment Type Concentration Risk        
Schedule of Investments [Line Items]        
Concentration risk (as a percent) 2.00%     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 17 19 69  
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% 30.00% 95.00%  
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 19 59  
Percentage of portfolio with annual third-party appraisal was obtained, reviewed and certified (as a percent)     94.00%  
Private Loan portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk        
Schedule of Investments [Line Items]        
Concentration risk (as a percent) 27.00% 25.00% 79.00%  
Middle Market portfolio investments        
Schedule of Investments [Line Items]        
Percentage of portfolio investments containing limited consultation with financial advisory services firm (as a percent) 98.00%   98.00% 98.00%
Other Portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk        
Schedule of Investments [Line Items]        
Concentration risk (as a percent) 3.10%     3.30%
Other Portfolio investments | Investment Owned, At Cost | Investment Type Concentration Risk        
Schedule of Investments [Line Items]        
Concentration risk (as a percent) 3.60%     4.00%