v3.26.1
Fair Value of Financial Instruments - Summary of Investments, Cash and Cash Equivalents, Credit Facility, or Prior Credit Facility, Notes and Asset Backed Debt (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Sep. 30, 2025
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments $ 2,580,281 $ 2,773,328
Cash and cash equivalents 31,427 40,729
Total investments and cash and cash equivalents 2,611,708 2,814,057
Long Term Credit Facility payable 328,333 683,837
Total debt 1,667,699 1,776,770
2026 Notes Payable    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 184,998 184,609
2029 Notes Payable    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 195,868  
2038-R Asset-Backed Debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 284,770  
2036 Asset-Backed Debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1]   284,627
2036 R Asset-Backed Debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 286,585 265,366
2037 Asset-Backed Debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 387,145 358,331
First lien    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 2,252,128 2,513,631
Second lien    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments   18,981
Subordinate debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 18,813  
Equity    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 309,340 240,716
Level 1    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 0 0
Cash and cash equivalents 31,427 40,729
Total investments and cash and cash equivalents 31,427 40,729
Long Term Credit Facility payable 0
Total debt 0 0
Level 1 | 2026 Notes Payable    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 0 0
Level 1 | 2029 Notes Payable    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 0  
Level 1 | 2038-R Asset-Backed Debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 0  
Level 1 | 2036 Asset-Backed Debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1]   0
Level 1 | 2036 R Asset-Backed Debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 0 0
Level 1 | 2037 Asset-Backed Debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 0  
Level 1 | First lien    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 0 0
Level 1 | Second lien    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments   0
Level 1 | Subordinate debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 0  
Level 1 | Equity    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 0 0
Level 2    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 0 0
Cash and cash equivalents 0 0
Total investments and cash and cash equivalents 0 0
Long Term Credit Facility payable 0 0
Total debt 380,866 184,609
Level 2 | 2026 Notes Payable    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 184,998 184,609
Level 2 | 2029 Notes Payable    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 195,868  
Level 2 | 2038-R Asset-Backed Debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 0  
Level 2 | 2036 Asset-Backed Debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1]   0
Level 2 | 2036 R Asset-Backed Debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 0 0
Level 2 | 2037 Asset-Backed Debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 0  
Level 2 | First lien    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 0 0
Level 2 | Second lien    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments   0
Level 2 | Subordinate debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 0  
Level 2 | Equity    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 0 0
Level 3    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 2,492,286 2,729,010
Cash and cash equivalents 0 0
Total investments and cash and cash equivalents 2,492,286 2,729,010
Long Term Credit Facility payable 328,333 683,837
Total debt 1,286,833 1,592,161
Level 3 | 2026 Notes Payable    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 0 0
Level 3 | 2029 Notes Payable    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 0  
Level 3 | 2038-R Asset-Backed Debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 284,770  
Level 3 | 2036 Asset-Backed Debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1]   284,627
Level 3 | 2036 R Asset-Backed Debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 286,585 265,366
Level 3 | 2037 Asset-Backed Debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 387,145 358,331
Level 3 | First lien    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 2,252,128 2,513,631
Level 3 | Second lien    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments   18,981
Level 3 | Subordinate debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 18,813  
Level 3 | Equity    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 221,345 196,398
Measured at Net Asset Value    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments [2] 87,995 44,318 [3]
Cash and cash equivalents [2] 0 0 [3]
Total investments and cash and cash equivalents [2] 87,995 44,318 [3]
Long Term Credit Facility payable [2] 0 0 [3]
Total debt [2] 0 0 [3]
Measured at Net Asset Value | 2026 Notes Payable    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1],[2] 0 0
Measured at Net Asset Value | 2029 Notes Payable    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1],[2] 0  
Measured at Net Asset Value | 2038-R Asset-Backed Debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1],[2] 0  
Measured at Net Asset Value | 2036 Asset-Backed Debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1],[2]   0
Measured at Net Asset Value | 2036 R Asset-Backed Debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1],[2] 0 0
Measured at Net Asset Value | 2037 Asset-Backed Debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt 0 [1],[2] 0 [3],[4]
Measured at Net Asset Value | First lien    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 0 [2] 0 [3],[4]
Measured at Net Asset Value | Second lien    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments [2],[3]   0
Measured at Net Asset Value | Subordinate debt    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments [2] 0  
Measured at Net Asset Value | Equity    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments [2] $ 87,995 $ 44,318 [3]
[1] We elected not to apply the fair value option allowed by ASC 825-10 to the 2026 Notes, 2029 Notes, 2038-R Asset-Backed Debt, 2036-R Asset-Backed Debt, and 2037 Asset-Backed Debt and thus the balance reported in the Consolidated Statement of Assets and Liabilities represents the carrying value, which approximates the fair value.
[2] In accordance with ASC Subtopic 820-10, Fair Value Measurements and Disclosures, or ASC 820-10, our equity investments in PSSL and PSSL II are measured using net asset value per share (or its equivalent) as a practical expedient for fair value, and thus have not been classified in the fair value hierarchy.
[3] In accordance with ASC Subtopic 820-10, Fair Value Measurements and Disclosures, or ASC 820-10, our equity investments in PSSL is measured using net asset value per share (or its equivalent) as a practical expedient for fair value in accordance with the specialized accounting guidance for investment companies, and thus has not been classified in the fair value hierarchy.
[4] We elected not to apply the fair value option allowed by ASC 825-10 to the 2026 Notes, 2036 Asset-Backed Debt, the 2036-R Asset-Backed Debt, and the 2037 Asset-Backed Debt and thus the balance reported in the Consolidated Statement of Assets and Liabilities represents the carrying value, which approximates the fair value.