Quarterly report [Sections 13 or 15(d)]

DEBT - Notes??Due and SBIC Debentures (Details)

v3.25.2
DEBT - Notes Due and SBIC Debentures (Details)
 1 Months Ended 6 Months Ended
Sep. 30, 2024
USD ($)
Jun. 30, 2024
USD ($)
May 31, 2024
USD ($)
Jan. 31, 2024
USD ($)
Oct. 31, 2021
USD ($)
Jan. 31, 2021
USD ($)
Jun. 30, 2025
USD ($)
Jun. 30, 2024
USD ($)
Dec. 31, 2024
USD ($)
Feb. 28, 2023
USD ($)
Dec. 31, 2022
USD ($)
agency
Debt Instrument [Line Items]                      
Debt instrument, outstanding balance             $ 2,227,000,000   $ 2,134,000,000    
Debt             2,216,984,000   2,122,371,000    
July 2026 Notes | Unsecured Notes                      
Debt Instrument [Line Items]                      
Debt instrument, face amount         $ 200,000,000.0 $ 300,000,000.0 500,000,000   500,000,000    
Debt instrument, interest rate, stated (as a percent)           3.00%          
Debt instrument, issuance price (as a percent)         101.741% 99.004%          
Debt instrument, outstanding balance             500,000,000   500,000,000    
Debt             499,452,000   499,188,000    
June 2027 Notes | Unsecured Notes                      
Debt Instrument [Line Items]                      
Debt instrument, face amount $ 400,000,000.0 $ 300,000,000.0         400,000,000 $ 300,000,000.0 400,000,000    
Debt instrument, interest rate, stated (as a percent)   6.50%           6.50%      
Debt instrument, issuance price (as a percent) 102.134% 99.793%                  
Yield to maturity rate   6.34%           6.34%      
Debt instrument, outstanding balance             400,000,000   400,000,000    
Debt             399,425,000   399,282,000    
June 2027 Notes, Additional | Unsecured Notes                      
Debt Instrument [Line Items]                      
Debt instrument, face amount $ 100,000,000.0                    
Yield to maturity rate   5.617%           5.617%      
March 2029 Notes | Unsecured Notes                      
Debt Instrument [Line Items]                      
Debt instrument, face amount       $ 350,000,000.0     350,000,000   350,000,000    
Debt instrument, interest rate, stated (as a percent)       6.95%              
Debt instrument, issuance price (as a percent)       99.865%              
Debt instrument, outstanding balance             350,000,000   350,000,000    
Debt             347,361,000   347,002,000    
SBIC debentures                      
Debt Instrument [Line Items]                      
Repayments of debt             0 $ 63,800,000      
SBIC debentures | Unsecured Notes                      
Debt Instrument [Line Items]                      
Debt instrument, face amount             350,000,000   350,000,000    
Debt instrument, outstanding balance             $ 350,000,000   $ 350,000,000    
Debt instrument, term (in years)             10 years        
Debt instrument, weighted-average annual interest rate (as a percent)             3.30%   3.30%    
Debt instrument, remaining term (in years)             5 years 1 month 6 days        
Debt             $ 344,005,000   $ 343,417,000    
SBIC debentures | Unsecured Notes | MSMF                      
Debt Instrument [Line Items]                      
Debt instrument, face amount             175,000,000.0        
Debt             170,600,000        
Debt instrument, unamortized debt issuance costs             4,400,000        
SBIC debentures | Unsecured Notes | MSC III                      
Debt Instrument [Line Items]                      
Debt instrument, face amount             175,000,000.0        
Debt             173,400,000        
Debt instrument, unamortized debt issuance costs             1,600,000        
SBIC debentures | Unsecured Notes | Maximum                      
Debt Instrument [Line Items]                      
Debt instrument, outstanding balance             350,000,000.0        
December 2025 Notes | Unsecured Notes                      
Debt Instrument [Line Items]                      
Debt instrument, face amount             150,000,000   150,000,000    
Debt instrument, outstanding balance             150,000,000   150,000,000    
Debt             $ 149,741,000   $ 149,482,000    
Debt instrument, credit rating, below investment grade event, percentage of agencies (as a percent)                     67.00%
Debt instrument, secured debt ratio event                     0.35
December 2025 Notes | Unsecured Notes | Maximum                      
Debt Instrument [Line Items]                      
Debt instrument, credit rating, below investment grade rating, number of agencies | agency                     2
December 2025 Notes | Unsecured Notes | Minimum                      
Debt Instrument [Line Items]                      
Debt instrument, credit rating, below investment grade rating, number of agencies | agency                     1
December 2025 Series A Notes | Unsecured Notes                      
Debt Instrument [Line Items]                      
Debt instrument, face amount                     $ 100,000,000.0
Debt instrument, interest rate, stated (as a percent)                     7.84%
December 2025 Series B Notes | Unsecured Notes                      
Debt Instrument [Line Items]                      
Debt instrument, face amount                   $ 50,000,000.0  
Debt instrument, interest rate, stated (as a percent)                   7.53%  
May 2024 Notes | Unsecured Notes                      
Debt Instrument [Line Items]                      
Debt instrument, interest rate, stated (as a percent)     5.20%                
Repayments of debt     $ 450,000,000.0