v3.25.2
Borrowings - Schedule of Interest Rate and Interest Differential Analysis (Details) - USD ($)
$ in Thousands
9 Months Ended
Nov. 18, 2024
Jun. 30, 2025
Sep. 30, 2024
Debt Instrument [Line Items]      
Amount Outstanding   $ 5,127,148 $ 4,599,430
2024 Debt Securitization      
Debt Instrument [Line Items]      
Interest Rate   4.30%  
2024 Debt Securitization | AAA/AAA Class A -1R 2024 Notes      
Debt Instrument [Line Items]      
Interest Rate 1.56%    
2024 Debt Securitization | AAA Class A-2RR 2024 Notes      
Debt Instrument [Line Items]      
Interest Rate 1.75%    
2024 Debt Securitization | Senior Notes | AAA/AAA Class A -1R 2024 Notes      
Debt Instrument [Line Items]      
Amount Outstanding   $ 1,192,400  
Interest Rate   1.56%  
2024 Debt Securitization | Senior Notes | AAA Class A-2RR 2024 Notes      
Debt Instrument [Line Items]      
Amount Outstanding   $ 171,600  
Interest Rate   1.75%  
GBDC 3 2022 Debt Securitization      
Debt Instrument [Line Items]      
Interest Rate   4.30%  
GBDC 3 2022 Debt Securitization | Senior Notes      
Debt Instrument [Line Items]      
Amount Outstanding   $ 179,529  
Interest Rate   2.00%