v3.25.2
Borrowings - 2018 Debt Securitization (Narrative) (Details)
$ in Thousands
 9 Months Ended
Nov. 16, 2018
USD ($)
Jun. 30, 2025
USD ($)
Sep. 30, 2024
USD ($)
portfolioCompany
Debt Instrument [Line Items]      
Investments, at fair value   $ 8,961,549 [1] $ 8,235,411 [2]
2018 Debt Securitization      
Debt Instrument [Line Items]      
Debt instrument, face amount $ 602,400    
Debt instrument, basis spread on variable rate   0.26161%  
Number of investment portfolio company | portfolioCompany     44
Investments, at fair value     $ 351,446
2018 Debt Securitization | Subordinated debt      
Debt Instrument [Line Items]      
Debt instrument, face amount 113,400    
2018 Debt Securitization | AAA/AAA Class A 2018 Notes      
Debt Instrument [Line Items]      
Debt instrument, face amount $ 327,000    
Debt instrument, basis spread on variable rate 1.48%    
2018 Debt Securitization | AA Class B 2018 Notes      
Debt Instrument [Line Items]      
Debt instrument, face amount $ 61,200    
Debt instrument, basis spread on variable rate 2.10%    
2018 Debt Securitization | A Class C-1 2018 Notes      
Debt Instrument [Line Items]      
Debt instrument, face amount $ 20,000    
Debt instrument, basis spread on variable rate 2.80%    
2018 Debt Securitization | A Class C-2 2018 Notes      
Debt Instrument [Line Items]      
Debt instrument, face amount $ 38,800    
Debt instrument, basis spread on variable rate 2.65%    
2018 Debt Securitization | BBB- Class D 2018 Notes      
Debt Instrument [Line Items]      
Debt instrument, face amount $ 42,000    
Debt instrument, basis spread on variable rate 2.95%    
[1] The fair values of investments were valued using significant unobservable inputs, unless noted otherwise. See Note 6.
[2] The fair values of investments were valued using significant unobservable inputs, unless noted otherwise. See Note 6.