Quarterly report pursuant to Section 13 or 15(d)

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

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DEBT - Schedule of Notes Due and SBIC Debentures (Details)
1 Months Ended 9 Months Ended
Oct. 31, 2021
USD ($)
Jan. 31, 2021
USD ($)
Jul. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Apr. 30, 2019
USD ($)
Nov. 30, 2017
USD ($)
Sep. 30, 2023
USD ($)
Feb. 28, 2023
USD ($)
Dec. 31, 2022
USD ($)
agency
Debt Instrument [Line Items]                  
Debt instrument, payable             $ 1,943,000,000   $ 2,007,000,000
Debt instrument             1,934,922,000   $ 1,999,102,000
Unsecured Notes                  
Debt Instrument [Line Items]                  
Debt instrument, weighted-average annual interest rate (as a percent)                 2.90%
July 2026 Notes | Unsecured Notes                  
Debt Instrument [Line Items]                  
Debt instrument, face amount $ 200,000,000 $ 300,000,000         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 instrument             498,530,000   498,136,000
May 2024 Notes | Unsecured Notes                  
Debt Instrument [Line Items]                  
Debt instrument, face amount     $ 125,000,000 $ 75,000,000 $ 250,000,000   450,000,000   450,000,000
Debt instrument, interest rate, stated (as a percent)         5.20%        
Debt instrument, issuance price (as a percent)     102.70% 105.00% 99.125%        
Debt instrument, payable             450,000,000   450,000,000
Debt instrument             450,318,000   450,727,000
SBIC Debentures | Unsecured Notes                  
Debt Instrument [Line Items]                  
Debt instrument, face amount             350,000,000   350,000,000
Debt instrument, payable             $ 350,000,000   350,000,000
Debt instrument, term (in years)             10 years    
Debt instrument, weighted-average annual interest rate (as a percent)             3.00%    
Debt instrument, remaining term (in years)             4 years 10 months 24 days    
Debt instrument             $ 344,239,000   343,914,000
SBIC Debentures | Unsecured Notes | Maximum                  
Debt Instrument [Line Items]                  
Debt instrument, payable             350,000,000    
SBIC Debentures | Unsecured Notes | MSMF                  
Debt Instrument [Line Items]                  
Debt instrument, face amount             175,000,000    
Debt instrument             171,900,000    
Debt instrument, unamortized debt issuance costs             3,100,000    
SBIC Debentures | Unsecured Notes | MSC III                  
Debt Instrument [Line Items]                  
Debt instrument, face amount             175,000,000    
Debt instrument             172,300,000    
Debt instrument, unamortized debt issuance costs             2,700,000    
December 2025 Notes | Unsecured Notes                  
Debt Instrument [Line Items]                  
Debt instrument, face amount             150,000,000   100,000,000
Debt instrument, payable             150,000,000   100,000,000
Debt instrument             $ 148,835,000   $ 99,325,000
Debt instrument, credit rating, below investment grade event, percentage of agencies                 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
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  
Debt instrument, interest rate, stated (as a percent)               7.53%  
December 2022 Notes | Unsecured Notes                  
Debt Instrument [Line Items]                  
Debt instrument, face amount           $ 185,000,000      
Debt instrument, interest rate, stated (as a percent)           4.50%      
Debt instrument, issuance price (as a percent)           99.16%