Quarterly report [Sections 13 or 15(d)]

RELATED PARTY TRANSACTIONS - Narrative (Details)

v3.26.1
RELATED PARTY TRANSACTIONS - Narrative (Details)
 1 Months Ended 3 Months Ended
Jan. 31, 2025
USD ($)
plan
Nov. 30, 2024
USD ($)
Sep. 30, 2023
USD ($)
Mar. 31, 2022
USD ($)
Feb. 28, 2022
USD ($)
Dec. 31, 2020
USD ($)
Mar. 31, 2026
USD ($)
shares
MSC Income              
Related Party Transaction [Line Items]              
Share repurchase program, authorized, amount $ 65,000,000.0            
Related Party | 2015 Deferred Compensation Plan              
Related Party Transaction [Line Items]              
Amounts of transaction             $ 32,400,000
Related Party | 2015 Deferred Compensation Plan | Rabbi Trust              
Related Party Transaction [Line Items]              
Amounts of transaction             $ 21,900,000
Related Party | 2015 Deferred Compensation Plan | Common Stock              
Related Party Transaction [Line Items]              
Deferred compensation (in shares) | shares             199,535
Related Party | 2015 Deferred Compensation Plan | Phantom Stock Units              
Related Party Transaction [Line Items]              
Amounts of transaction             $ 10,600,000
External Investment Manager | Related Party              
Related Party Transaction [Line Items]              
Accounts receivable from MSCC and its subsidiaries             11,300,000
External Investment Manager | Related Party | Operating Expenses and Amount Due From Tax Sharing Agreement              
Related Party Transaction [Line Items]              
Accounts receivable from MSCC and its subsidiaries             8,500,000
External Investment Manager | Related Party | Dividends Declared But Not Yet Paid              
Related Party Transaction [Line Items]              
Accounts receivable from MSCC and its subsidiaries             2,900,000
MSC Income              
Related Party Transaction [Line Items]              
Share purchase program, authorized, amount $ 20,000,000.0            
Share purchase program, period in force 12 months            
Share purchase (repurchase) program, number of active plans | plan 2            
Share purchase program, percentage of outstanding stock maximum (as a percent) 3.00%            
MSC Income | Related Party              
Related Party Transaction [Line Items]              
Share repurchase program, authorized, amount             $ 20,000,000.0
Units (in shares) | shares             2,025,220
MSC Income | Related Party | Unsecured Revolving Promissory Note              
Related Party Transaction [Line Items]              
Amounts of transaction             $ 30,000,000.0
Interest rate (as a percent)             4.50%
Interest rate, floor (as a percent)             2.00%
Unused capacity, commitment fee (as a percent)             0.25%
MSC Income | Related Party | Secured Revolving Promissory Note              
Related Party Transaction [Line Items]              
Amount of debt outstanding             $ 0
Private Loan Fund I | Related Party | Investment Management Agreement              
Related Party Transaction [Line Items]              
Amounts of transaction         $ 15,000,000.0 $ 10,000,000.0  
Funded commitments             15,000,000.0
Private Loan Fund I | Related Party | Secured Revolving Promissory Note              
Related Party Transaction [Line Items]              
Amounts of transaction       $ 20,000,000.0      
Interest rate (as a percent)       3.00%      
Interest rate, floor (as a percent)       2.00%      
Unused capacity, commitment fee (as a percent)       0.25%      
Amount of debt outstanding             12,300,000
Private Loan Fund I | Related Party | 2015 Deferred Compensation Plan | Rabbi Trust              
Related Party Transaction [Line Items]              
Amounts of transaction             2,200,000
Private Loan Fund II | Related Party | Investment Management Agreement              
Related Party Transaction [Line Items]              
Amounts of transaction     $ 15,000,000.0        
Funded commitments             10,500,000
Percentage of total commitments (as a percent)     20.00%        
Unfunded commitments             4,500,000
Private Loan Fund II | Related Party | Secured Revolving Promissory Note              
Related Party Transaction [Line Items]              
Amounts of transaction   $ 10,000,000.0          
Interest rate (as a percent)   3.00%          
Interest rate, floor (as a percent)   2.00%          
Unused capacity, commitment fee (as a percent)   0.25%          
Amount of debt outstanding             0
Private Loan Fund II | Related Party | 2015 Deferred Compensation Plan | Rabbi Trust              
Related Party Transaction [Line Items]              
Amounts of transaction             $ 5,300,000