v3.25.2
Portfolio Investments - Schedule of Financial Instruments Carried at Fair Value (Details) - USD ($)
$ in Thousands
Jun. 30, 2025
Sep. 30, 2024
Schedule of Investments [Line Items]    
Investments at fair value $ 2,809,377 $ 3,021,279
Cash equivalents 19,679 34,597
Derivative assets 7,910  
Total assets at fair value 2,836,966 3,055,876
Derivative liabilities 16,802 16,843
Total liabilities at fair value 16,802 16,843
Senior secured debt    
Schedule of Investments [Line Items]    
Investments at fair value 2,343,411 2,574,937
Subordinated debt securities, including JV debt instruments CLO Notes    
Schedule of Investments [Line Items]    
Investments at fair value 297,842 271,473
Preferred equity    
Schedule of Investments [Line Items]    
Investments at fair value 73,232 66,320
Equity Securities, Common And Warrants, Including JV Investments    
Schedule of Investments [Line Items]    
Investments at fair value 94,892 108,549
Level 1    
Schedule of Investments [Line Items]    
Investments at fair value 743 1,422
Cash equivalents 19,679 34,597
Derivative assets 0  
Total assets at fair value 20,422 36,019
Derivative liabilities 0 0
Total liabilities at fair value 0 0
Level 1 | Senior secured debt    
Schedule of Investments [Line Items]    
Investments at fair value 0 0
Level 1 | Subordinated debt securities, including JV debt instruments CLO Notes    
Schedule of Investments [Line Items]    
Investments at fair value 0 0
Level 1 | Preferred equity    
Schedule of Investments [Line Items]    
Investments at fair value 0 0
Level 1 | Equity Securities, Common And Warrants, Including JV Investments    
Schedule of Investments [Line Items]    
Investments at fair value 743 1,422
Level 2    
Schedule of Investments [Line Items]    
Investments at fair value 308,431 273,584
Cash equivalents 0 0
Derivative assets 7,910  
Total assets at fair value 316,341 273,584
Derivative liabilities 16,802 16,843
Total liabilities at fair value 16,802 16,843
Level 2 | Senior secured debt    
Schedule of Investments [Line Items]    
Investments at fair value 266,566 254,627
Level 2 | Subordinated debt securities, including JV debt instruments CLO Notes    
Schedule of Investments [Line Items]    
Investments at fair value 40,344 16,127
Level 2 | Preferred equity    
Schedule of Investments [Line Items]    
Investments at fair value 0 0
Level 2 | Equity Securities, Common And Warrants, Including JV Investments    
Schedule of Investments [Line Items]    
Investments at fair value 1,521 2,830
Level 3    
Schedule of Investments [Line Items]    
Investments at fair value 2,485,322 2,723,732
Cash equivalents 0 0
Derivative assets 0  
Total assets at fair value 2,485,322 2,723,732
Derivative liabilities 0 0
Total liabilities at fair value 0 0
Level 3 | Senior secured debt    
Schedule of Investments [Line Items]    
Investments at fair value 2,076,845 2,320,310
Level 3 | Subordinated debt securities, including JV debt instruments CLO Notes    
Schedule of Investments [Line Items]    
Investments at fair value 257,498 255,346
Level 3 | Preferred equity    
Schedule of Investments [Line Items]    
Investments at fair value 73,232 66,320
Level 3 | Equity Securities, Common And Warrants, Including JV Investments    
Schedule of Investments [Line Items]    
Investments at fair value 77,747 81,756
Measured at Net Asset Value    
Schedule of Investments [Line Items]    
Investments at fair value 14,881 22,541
Cash equivalents 0 0
Derivative assets 0  
Total assets at fair value 14,881 22,541
Derivative liabilities 0 0
Total liabilities at fair value 0 0
Measured at Net Asset Value | Senior secured debt    
Schedule of Investments [Line Items]    
Investments at fair value 0 0
Measured at Net Asset Value | Subordinated debt securities, including JV debt instruments CLO Notes    
Schedule of Investments [Line Items]    
Investments at fair value 0 0
Measured at Net Asset Value | Preferred equity    
Schedule of Investments [Line Items]    
Investments at fair value 0 0
Measured at Net Asset Value | Equity Securities, Common And Warrants, Including JV Investments    
Schedule of Investments [Line Items]    
Investments at fair value $ 14,881 $ 22,541