Quarterly report pursuant to Section 13 or 15(d)

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)

v3.22.2.2
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)
$ in Millions
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2022
USD ($)
company
investment
Sep. 30, 2021
company
Sep. 30, 2022
USD ($)
company
investment
Sep. 30, 2021
company
Dec. 31, 2021
investment
Schedule of Investments [Line Items]          
Cash exceeded Federal Deposit Insurance Corporation insurance protection levels | $ $ 58.2   $ 58.2    
Percentage of total investment income, attributable to noncash paid-in-kind interest income 1.20% 2.10% 1.30% 3.00%  
Percentage of total investment come, attributable to noncash cumulative dividend income 0.30% 0.60% 0.50% 0.60%  
Percentage of total investment income, attributable to interest income, debt investments, net 1.80% 1.80% 1.90% 2.10%  
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 11   11   9
Non-accrual Status | Investment Owned, At Fair Value | Investment Type Concentration Risk          
Schedule of Investments [Line Items]          
Concentration risk, percentage     0.80%   0.70%
Non-accrual Status | Investment Owned, At Cost | Investment Type Concentration Risk          
Schedule of Investments [Line Items]          
Concentration risk, percentage     3.70%   3.30%
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 51 43 51 43  
Percentage of portfolio with annual third-party appraisal was obtained, reviewed and certified     80.00% 74.00%  
LMM portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk          
Schedule of Investments [Line Items]          
Concentration risk, percentage     80.00% 70.00%  
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 40 31 40 31  
Percentage of portfolio with annual third-party appraisal was obtained, reviewed and certified     70.00% 75.00%  
Private Loan portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk          
Schedule of Investments [Line Items]          
Concentration risk, percentage     50.00% 57.00%  
Middle Market portfolio investments          
Schedule of Investments [Line Items]          
Percentage of portfolio investments containing limited consultation with financial advisory services firm 95.00%   95.00%   93.00%
Other Portfolio investments | Investment Owned, At Fair Value | Investment Type Concentration Risk          
Schedule of Investments [Line Items]          
Concentration risk, percentage     2.90%   4.70%
Other Portfolio investments | Investment Owned, At Cost | Investment Type Concentration Risk          
Schedule of Investments [Line Items]          
Concentration risk, percentage     3.30%   5.30%