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, 2023
USD ($)
investment
company
Mar. 31, 2022
company
Dec. 31, 2022
investment
Schedule of Investments [Line Items]      
Cash exceeded Federal Deposit Insurance Corporation insurance protection levels | $ $ 35.2    
Percentage of total investment income, attributable to noncash paid-in-kind interest income 2.40% 1.20%  
Percentage of total investment come, attributable to noncash cumulative dividend income 0.30% 1.10%  
Percentage of total investment income, attributable to interest income, debt investments, net 1.80% 2.00%  
Investment Owned, At Fair Value | Investment Type Concentration Risk      
Schedule of Investments [Line Items]      
Concentration risk, percentage 100.00%   100.00%
Investment Owned, At Cost | Investment Type Concentration Risk      
Schedule of Investments [Line Items]      
Concentration risk, percentage 100.00%   100.00%
Non-accrual Status      
Schedule of Investments [Line Items]      
Number of investments | investment 13   12
Non-accrual Status | Investment Owned, At Fair Value | Investment Type Concentration Risk      
Schedule of Investments [Line Items]      
Concentration risk, percentage 0.60%   0.60%
Non-accrual Status | Investment Owned, At Cost | Investment Type Concentration Risk      
Schedule of Investments [Line Items]      
Concentration risk, percentage 3.20%   3.70%
Revolving Credit Facility | Line of Credit      
Schedule of Investments [Line Items]      
Commitment fee (in percentage) 3.40%    
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 19 19  
Percentage of portfolio with annual third-party appraisal was obtained, reviewed and certified 32.00% 36.00%  
LMM portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk      
Schedule of Investments [Line Items]      
Concentration risk, percentage 30.00% 30.00%  
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 19 18  
Percentage of portfolio with annual third-party appraisal was obtained, reviewed and certified 28.00% 42.00%  
Private Loan portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk      
Schedule of Investments [Line Items]      
Concentration risk, percentage 25.00% 26.00%  
Middle Market portfolio investments      
Schedule of Investments [Line Items]      
Percentage of portfolio investments containing limited consultation with financial advisory services firm 90.00%   89.00%
Other Portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk      
Schedule of Investments [Line Items]      
Concentration risk, percentage 2.80%   2.80%
Other Portfolio investments | Investment Owned, At Cost | Investment Type Concentration Risk      
Schedule of Investments [Line Items]      
Concentration risk, percentage 3.20%   3.20%