Quarterly report [Sections 13 or 15(d)]

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

v3.25.1
DEBT - Notes Due and SBIC Debentures (Details)
1 Months Ended 3 Months Ended
Sep. 30, 2024
USD ($)
Jun. 30, 2024
USD ($)
May 31, 2024
USD ($)
Mar. 31, 2024
USD ($)
Jan. 31, 2024
USD ($)
Oct. 31, 2021
USD ($)
Jan. 31, 2021
USD ($)
Mar. 31, 2025
USD ($)
Mar. 31, 2024
USD ($)
Dec. 31, 2024
USD ($)
Feb. 28, 2023
USD ($)
Dec. 31, 2022
USD ($)
agency
Debt Instrument [Line Items]                        
Debt instrument, payable               $ 2,264,000,000   $ 2,134,000,000    
Debt               2,253,179,000   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, payable               500,000,000   500,000,000    
Debt               499,320,000   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   400,000,000    
Debt instrument, interest rate, stated (as a percent) 6.34% 6.50%                    
Debt instrument, issuance price (as a percent) 102.134% 99.793%                    
Debt instrument, payable               400,000,000   400,000,000    
Debt               399,354,000   399,282,000    
June 2027 Notes, Additional | Unsecured Notes                        
Debt Instrument [Line Items]                        
Debt instrument, face amount $ 100,000,000.0                      
Debt instrument, interest rate, stated (as a percent) 5.617%                      
March 2029 Notes                        
Debt Instrument [Line Items]                        
Proceeds from public offering of March 2029 Notes               0 $ 350,000,000      
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, payable               350,000,000   350,000,000    
Debt               347,182,000   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, payable $ 350,000,000.0     $ 286,200,000       $ 350,000,000 $ 286,200,000 $ 350,000,000    
Repayments of debt       $ 63,800,000                
Proceeds from public offering of March 2029 Notes $ 63,800,000                      
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 4 months 24 days        
Debt               $ 343,711,000   $ 343,417,000    
SBIC Debentures | Unsecured Notes | MSMF                        
Debt Instrument [Line Items]                        
Debt instrument, face amount               175,000,000.0        
Debt               170,500,000        
Debt instrument, unamortized debt issuance costs               4,500,000        
SBIC Debentures | Unsecured Notes | MSC III                        
Debt Instrument [Line Items]                        
Debt instrument, face amount               175,000,000.0        
Debt               173,200,000        
Debt instrument, unamortized debt issuance costs               1,800,000        
SBIC Debentures | Unsecured Notes | Maximum                        
Debt Instrument [Line Items]                        
Debt instrument, payable               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, payable               150,000,000   150,000,000    
Debt               $ 149,612,000   $ 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