Annual report pursuant to Section 13 and 15(d)

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)

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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2022
USD ($)
company
investment
Dec. 31, 2021
company
investment
Dec. 31, 2020
Schedule of Investments [Line Items]      
Cash exceeded Federal Deposit Insurance Corporation insurance protection levels | $ $ 46.3    
Percentage of total investment income, attributable to noncash paid-in-kind interest income 1.40% 2.60% 2.80%
Percentage of total investment come, attributable to noncash cumulative dividend income 0.50% 0.60% 0.80%
Percentage of total investment income, attributable to interest income, debt investments, net 1.80% 2.00% 2.70%
Credit Facility      
Schedule of Investments [Line Items]      
Commitment fee (in percentage) 3.40%    
Non-accrual Status      
Schedule of Investments [Line Items]      
Number of investments | investment 12 9  
Investment Owned, At Fair Value | Investment Type Concentration Risk      
Schedule of Investments [Line Items]      
Concentration risk, percentage 100.00% 100.00%  
Investment Owned, At Fair Value | Investment Type Concentration Risk | Non-accrual Status      
Schedule of Investments [Line Items]      
Concentration risk, percentage 0.60% 0.70%  
Investment Owned, At Cost | Investment Type Concentration Risk      
Schedule of Investments [Line Items]      
Concentration risk, percentage 100.00% 100.00%  
Investment Owned, At Cost | Investment Type Concentration Risk | Non-accrual Status      
Schedule of Investments [Line Items]      
Concentration risk, percentage 3.70% 3.30%  
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 66 54  
Percentage of portfolio with annual third-party appraisal was obtained, reviewed and certified 99.00% 99.00%  
LMM portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk      
Schedule of Investments [Line Items]      
Concentration risk, percentage 94.00% 81.00%  
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 59 39  
Percentage of portfolio with annual third-party appraisal was obtained, reviewed and certified 97.00% 93.00%  
Private Loan portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk      
Schedule of Investments [Line Items]      
Concentration risk, percentage 76.00% 60.00%  
Middle Market portfolio investments      
Schedule of Investments [Line Items]      
Percentage of portfolio investments containing limited consultation with financial advisory services firm 89.00% 93.00%  
Other Portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk      
Schedule of Investments [Line Items]      
Concentration risk, percentage 2.80% 4.70%  
Other Portfolio investments | Investment Owned, At Cost | Investment Type Concentration Risk      
Schedule of Investments [Line Items]      
Concentration risk, percentage 3.20% 5.30%