Quarterly report pursuant to Section 13 or 15(d)

RELATED PARTY TRANSACTIONS (Details)

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RELATED PARTY TRANSACTIONS (Details) - Related Party - USD ($)
 1 Months Ended 6 Months Ended
Sep. 30, 2023
Aug. 31, 2023
Mar. 31, 2022
Feb. 28, 2022
Dec. 31, 2020
Jun. 30, 2024
May 31, 2024
Jan. 31, 2024
Oct. 31, 2023
May 31, 2023
External Investment Manager                    
Related Party Transaction [Line Items]                    
Receivable           $ 9,800,000        
MSC Income                    
Related Party Transaction [Line Items]                    
Shares acquired (in shares)   348,542       1,919,596 315,259 314,070 475,888 255,755
Operating Expenses and Amount Due From Tax Sharing Agreement | External Investment Manager                    
Related Party Transaction [Line Items]                    
Receivable           $ 6,500,000        
Dividends Declared But Not Yet Paid | External Investment Manager                    
Related Party Transaction [Line Items]                    
Receivable           3,300,000        
Dutch Auction | MSC Income                    
Related Party Transaction [Line Items]                    
Shares acquired (in shares) 115,385                  
Sale of stock, price per share (in dollars per share) $ 6.50                  
Sale of stock, authorized consideration on transaction   $ 3,500,000                
Investment Management Agreement | Private Loan Fund                    
Related Party Transaction [Line Items]                    
Amounts of transaction       $ 15,000,000.0 $ 10,000,000.0          
Funded commitments           14,300,000        
Unfunded commitments           700,000        
Investment Management Agreement | Private Loan Fund II                    
Related Party Transaction [Line Items]                    
Amounts of transaction $ 15,000,000.0                  
Funded commitments           2,200,000        
Unfunded commitments           8,700,000        
Percentage of total commitments (as a percent) 20.00%                  
Secured Revolving Promissory Note | Private Loan Fund                    
Related Party Transaction [Line Items]                    
Amounts of transaction     $ 10,000,000.0              
Interest rate (as a percent)     5.00%              
Unused capacity, commitment fee (as a percent)     0.25%              
Amount of debt outstanding           7,000,000.0        
Secured Revolving Promissory Note | Private Loan Fund II                    
Related Party Transaction [Line Items]                    
Amounts of transaction $ 50,000,000.0                  
Interest rate (as a percent) 3.50%                  
Unused capacity, commitment fee (as a percent) 0.25%                  
Amount of debt outstanding           49,500,000        
Interest rate, floor (as a percent) 2.00%                  
2015 Deferred Compensation Plan                    
Related Party Transaction [Line Items]                    
Amounts of transaction           23,900,000        
2015 Deferred Compensation Plan | Rabbi Trust                    
Related Party Transaction [Line Items]                    
Amounts of transaction           $ 14,800,000        
2015 Deferred Compensation Plan | Common Stock                    
Related Party Transaction [Line Items]                    
Deferred compensation (in shares)           180,250        
2015 Deferred Compensation Plan | Phantom Stock Units                    
Related Party Transaction [Line Items]                    
Amounts of transaction           $ 9,100,000        
2015 Deferred Compensation Plan | Private Loan Fund | Rabbi Trust                    
Related Party Transaction [Line Items]                    
Amounts of transaction           2,100,000        
2015 Deferred Compensation Plan | Private Loan Fund II | Rabbi Trust                    
Related Party Transaction [Line Items]                    
Amounts of transaction           $ 3,600,000