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 ($)
company
investment
Mar. 31, 2022
company
Dec. 31, 2022
investment
Schedule of Investments [Line Items]      
Short-term money market account $ 7.5    
Money market funds 10.9    
Cash balances exceeded Federal Deposit Insurance Corporation insurance protection levels $ 18.5    
Percentage of total investment income, attributable to noncash paid-in-kind interest income 3.80% 1.80%  
Percentage of total investment come, attributable to noncash cumulative dividend income 0.10% 1.80%  
Percentage of total investment income, attributable to interest income, debt investments, net 2.50% 2.70%  
Nonperforming Financial Instruments      
Schedule of Investments [Line Items]      
Number of investments | investment 7   7
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 | Nonperforming Financial Instruments      
Schedule of Investments [Line Items]      
Concentration risk, percentage 0.70%   0.80%
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 | Nonperforming Financial Instruments      
Schedule of Investments [Line Items]      
Concentration risk, percentage 4.60%   4.80%
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 12  
Percentage of portfolio with annual third-party appraisal was obtained, reviewed and certified 26.00% 35.00%  
Private Loan portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk      
Schedule of Investments [Line Items]      
Concentration risk, percentage 24.00% 26.00%  
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 13 13  
Percentage of portfolio with annual third-party appraisal was obtained, reviewed and certified 41.00% 48.00%  
LMM portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk      
Schedule of Investments [Line Items]      
Concentration risk, percentage 39.00% 40.00%  
Middle Market portfolio investments      
Schedule of Investments [Line Items]      
Percentage of portfolio investments containing limited consultation with financial advisory services firm 93.00%   91.00%
Other Portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk      
Schedule of Investments [Line Items]      
Concentration risk, percentage 2.60%   2.70%
Other Portfolio investments | Investment Owned, At Cost | Investment Type Concentration Risk      
Schedule of Investments [Line Items]      
Concentration risk, percentage 2.20%   2.30%