v3.26.1
Fair Value of Financial Instruments - Summary of Investments, Cash and Cash Equivalents, Credit Facility, SBA Debentures and Notes (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 $ 1,203,513 $ 1,287,273
Cash Equivalents, Fair Value 15,070 30,711
Total investments and cash equivalents 1,218,583 1,317,984
Total debt 587,235 738,883
2026 Notes    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 149,923 149,473
2026 Notes-2    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 164,360 163,933
2029 Notes    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 73,472  
Truist Credit Facility    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Truist Credit Facility 199,480 425,477
Debt Investments    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 703,601 801,754
US Government Securities [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 209,427 124,788 [2]
Equity Investments    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 290,485 360,731
Level 1    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 0 0
Cash Equivalents, Fair Value 15,070 30,711
Total investments and cash equivalents 15,070 30,711
Total debt 0 0
Level 1 | 2026 Notes    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 0 [3] 0
Level 1 | 2026 Notes-2    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 0 [3] 0
Level 1 | 2029 Notes    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1],[3] 0  
Level 1 | Truist Credit Facility    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Truist Credit Facility 0 0
Level 1 | Debt Investments    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 0 0
Level 1 | US Government Securities [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 0 [4] 0 [2]
Level 1 | Equity Investments    
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 209,427 124,788
Cash Equivalents, Fair Value 0 0
Total investments and cash equivalents 209,427 124,788
Total debt 387,755 313,406
Level 2 | 2026 Notes    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 149,923 149,473
Level 2 | 2026 Notes-2    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 164,360 163,933
Level 2 | 2029 Notes    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 73,472  
Level 2 | Truist Credit Facility    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Truist Credit Facility 0 0
Level 2 | Debt Investments    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 0 0
Level 2 | US Government Securities [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments [2] 209,427 124,788
Level 2 | Equity Investments    
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 934,607 1,087,964
Cash Equivalents, Fair Value 0 0
Total investments and cash equivalents 934,607 1,087,964
Total debt 199,480 425,477
Level 3 | 2026 Notes    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 0 0
Level 3 | 2026 Notes-2    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 0 0
Level 3 | 2029 Notes    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1] 0  
Level 3 | Truist Credit Facility    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Truist Credit Facility 199,480 425,477
Level 3 | Debt Investments    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 703,601 801,754
Level 3 | US Government Securities [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 0 0 [2]
Level 3 | Equity Investments    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments 231,006 286,210
Measured at Net Asset Value    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments [6] 59,479 [5] 74,521
Cash Equivalents, Fair Value [6] 0 [5] 0
Total investments and cash equivalents [6] 59,479 [5] 74,521
Total debt [6] 0 [5] 0
Measured at Net Asset Value | 2026 Notes    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1],[6] 0 [3],[5] 0
Measured at Net Asset Value | 2026 Notes-2    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1],[6] 0 [3],[5] 0
Measured at Net Asset Value | 2029 Notes    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total debt [1],[3],[5],[6] 0  
Measured at Net Asset Value | Truist Credit Facility    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Truist Credit Facility [6] 0 [5] 0
Measured at Net Asset Value | Debt Investments    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments [6] 0 [5] 0
Measured at Net Asset Value | US Government Securities [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments [6] 0 [4],[5] 0 [2]
Measured at Net Asset Value | Equity Investments    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total investments [6] $ 59,479 [5] $ 74,521
[1] We elected not to apply ASC 825-10 to the 2026 Notes and thus the balance reported in the Consolidated Statement of Assets and Liabilities represents the carrying value.
[2] Our U.S. Treasury Bills are classified as Level 2, as they were valued by the pricing service which utilize broker-supplied prices.
[3] We elected not to apply ASC 825-10 to the 2026 Notes, the 2026 Notes-2, the 2029 Notes, and thus the balance reported in the Consolidated Statement of Assets and Liabilities represents the carrying value.
[4] Our U.S. Treasury Bills are classified as Level 2, as they were valued by the pricing service which utilize broker-supplied prices.
[5] In accordance with ASC Subtopic 820-10, Fair Value Measurements and Disclosures ("ASC 820-10"), our equity investment in PSLF and PTSF II are measured using the net asset value per share (or its equivalent) as a practical expedient for fair value, and thus has not been classified in the fair value hierarchy.
[6] In accordance with ASC Subtopic 820-10, Fair Value Measurements and Disclosures ("ASC 820-10"), our equity investment in PSLF and PTSF II are measured using the net asset value per share (or its equivalent) as a practical expedient for fair value, and thus has not been classified in the fair value hierarchy.