v3.26.1
Portfolio Investments - Schedule of Financial Instruments Carried at Fair Value (Details) - USD ($)
$ in Thousands
Jun. 30, 2026
Sep. 30, 2025
Schedule of Investments [Line Items]    
Investments at fair value $ 2,741,814 $ 2,847,782
Cash equivalents 33,372 6,608
Derivative assets 5,815 8,713
Total assets at fair value 2,781,001 2,863,103
Derivative liabilities 6,699 7,329
Total liabilities at fair value 6,699 7,329
Senior secured debt    
Schedule of Investments [Line Items]    
Investments at fair value 2,316,840 2,445,538
Subordinated debt securities, including JV debt instruments CLO Notes    
Schedule of Investments [Line Items]    
Investments at fair value 288,510 249,176
Preferred equity    
Schedule of Investments [Line Items]    
Investments at fair value 48,866 72,122
Equity Securities, Common And Warrants, Including JV Investments    
Schedule of Investments [Line Items]    
Investments at fair value 87,598 80,946
Level 1    
Schedule of Investments [Line Items]    
Investments at fair value 2,307 696
Cash equivalents 33,372 6,608
Derivative assets 0 0
Total assets at fair value 35,679 7,304
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 2,307 696
Level 2    
Schedule of Investments [Line Items]    
Investments at fair value 201,901 357,762
Cash equivalents 0 0
Derivative assets 5,815 8,713
Total assets at fair value 207,716 366,475
Derivative liabilities 6,699 7,329
Total liabilities at fair value 6,699 7,329
Level 2 | Senior secured debt    
Schedule of Investments [Line Items]    
Investments at fair value 156,168 338,232
Level 2 | Subordinated debt securities, including JV debt instruments CLO Notes    
Schedule of Investments [Line Items]    
Investments at fair value 45,733 18,039
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 0 1,491
Level 3    
Schedule of Investments [Line Items]    
Investments at fair value 2,508,878 2,477,378
Cash equivalents 0 0
Derivative assets 0 0
Total assets at fair value 2,508,878 2,477,378
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 2,160,672 2,107,306
Level 3 | Subordinated debt securities, including JV debt instruments CLO Notes    
Schedule of Investments [Line Items]    
Investments at fair value 242,777 231,137
Level 3 | Preferred equity    
Schedule of Investments [Line Items]    
Investments at fair value 48,866 72,122
Level 3 | Equity Securities, Common And Warrants, Including JV Investments    
Schedule of Investments [Line Items]    
Investments at fair value 56,563 66,813
Measured at Net Asset Value    
Schedule of Investments [Line Items]    
Investments at fair value 28,728 11,946
Cash equivalents 0 0
Derivative assets 0 0
Total assets at fair value 28,728 11,946
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 $ 28,728 $ 11,946