Quarterly report pursuant to Section 13 or 15(d)

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

v3.24.3
DEBT - Notes Due and SBIC Debentures (Details)
1 Months Ended 9 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 ($)
Sep. 30, 2024
USD ($)
Sep. 30, 2023
USD ($)
Dec. 31, 2023
USD ($)
Feb. 28, 2023
USD ($)
Dec. 31, 2022
USD ($)
agency
Debt Instrument [Line Items]                        
Debt instrument, payable $ 2,210,000,000             $ 2,210,000,000   $ 1,810,000,000    
Debt 2,199,490,000             2,199,490,000   1,802,344,000    
July 2026 Notes | Unsecured Notes                        
Debt Instrument [Line Items]                        
Debt instrument, face amount 500,000,000         $ 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   500,000,000    
Debt 499,057,000             499,057,000   498,662,000    
June 2027 Notes                        
Debt Instrument [Line Items]                        
Proceeds from debt               400,000,000 $ 0      
June 2027 Notes | Unsecured Notes                        
Debt Instrument [Line Items]                        
Debt instrument, face amount $ 400,000,000.0 $ 300,000,000.0           $ 400,000,000.0        
Debt instrument, interest rate, stated (as a percent) 6.34% 6.50%           6.34%        
Debt instrument, issuance price (as a percent) 102.134% 99.793%                    
Debt instrument, payable $ 400,000,000             $ 400,000,000        
Debt 401,136,000             401,136,000   0    
June 2027 Notes, Additional | Unsecured Notes                        
Debt Instrument [Line Items]                        
Debt instrument, face amount $ 100,000,000.0             $ 100,000,000.0        
Debt instrument, interest rate, stated (as a percent) 5.617%             5.617%        
March 2029 Notes                        
Debt Instrument [Line Items]                        
Proceeds from debt               $ 350,000,000 0      
March 2029 Notes | Unsecured Notes                        
Debt Instrument [Line Items]                        
Debt instrument, face amount $ 350,000,000       $ 350,000,000.0     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 346,822,000             346,822,000   0    
SBIC Debentures                        
Debt Instrument [Line Items]                        
Repayments of debt               63,800,000 16,000,000      
Proceeds from debt               63,800,000 16,000,000      
SBIC Debentures | Unsecured Notes                        
Debt Instrument [Line Items]                        
Debt instrument, face amount 350,000,000             350,000,000   350,000,000    
Debt instrument, payable 350,000,000     $ 286,200,000       $ 350,000,000   $ 350,000,000    
Repayments of debt       $ 63,800,000                
Proceeds from debt $ 63,800,000                      
Debt instrument, term (in years)               10 years        
Debt instrument, weighted-average annual interest rate (as a percent) 3.30%             3.30%   3.00%    
Debt instrument, remaining term (in years)               5 years 10 months 24 days        
Debt $ 343,122,000             $ 343,122,000   $ 344,535,000    
SBIC Debentures | Unsecured Notes | Maximum                        
Debt Instrument [Line Items]                        
Debt instrument, payable 350,000,000.0             350,000,000.0        
SBIC Debentures | Unsecured Notes | MSMF                        
Debt Instrument [Line Items]                        
Debt instrument, face amount 175,000,000.0             175,000,000.0        
Debt 170,200,000             170,200,000        
Debt instrument, unamortized debt issuance costs 4,800,000             4,800,000        
SBIC Debentures | Unsecured Notes | MSC III                        
Debt Instrument [Line Items]                        
Debt instrument, face amount 175,000,000.0             175,000,000.0        
Debt 172,900,000             172,900,000        
Debt instrument, unamortized debt issuance costs 2,100,000             2,100,000        
December 2025 Notes                        
Debt Instrument [Line Items]                        
Proceeds from debt               0 $ 50,000,000      
December 2025 Notes | Unsecured Notes                        
Debt Instrument [Line Items]                        
Debt instrument, face amount 150,000,000             150,000,000   150,000,000    
Debt instrument, payable 150,000,000             150,000,000   150,000,000    
Debt 149,353,000             149,353,000   148,965,000    
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 | Minimum                        
Debt Instrument [Line Items]                        
Debt instrument, credit rating, below investment grade rating, number of agencies | agency                       1
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 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, face amount                   450,000,000.0    
Debt instrument, interest rate, stated (as a percent)     5.20%                  
Debt instrument, payable                   450,000,000    
Repayments of debt     $ 450,000,000.0                  
Debt $ 0             $ 0   $ 450,182,000