Borrowings - Schedule of Long-term Debt (Details) - USD ($)	Jun. 30, 2024	Sep. 30, 2023
Debt Instrument [Line Items]
Total outstanding borrowings of unconsolidated entities	$ 1,069,408,000	$ 978,028,000
Unamortized debt issuance costs	(8,734,000)	(5,759,000)
Carrying Amount
Debt Instrument [Line Items]
Total financial liabilities	1,024,408,000	978,028,000
Senior Unsecured Revolving Credit Facility
Debt Instrument [Line Items]
Senior Unsecured Revolving Credit Facility	45,000,000.0	0
Senior Notes
Debt Instrument [Line Items]
Total outstanding borrowings of unconsolidated entities	948,521,000	903,691,000
Unamortized debt issuance costs	$ (8,734,000)	$ (5,759,000)
Senior Notes | 6.750%
Debt Instrument [Line Items]
Stated interest rate on debt instrument	6.75%	6.75%
Total outstanding borrowings of unconsolidated entities	$ 0	$ 202,195,000
Senior Notes | 5.875%
Debt Instrument [Line Items]
Stated interest rate on debt instrument	5.875%	5.875%
Total outstanding borrowings of unconsolidated entities	$ 357,255,000	$ 357,255,000
Senior Notes | 7.250%
Debt Instrument [Line Items]
Stated interest rate on debt instrument	7.25%	7.25%
Total outstanding borrowings of unconsolidated entities	$ 350,000,000	$ 350,000,000
Senior Notes | 7.500%
Debt Instrument [Line Items]
Stated interest rate on debt instrument	7.50%
Total outstanding borrowings of unconsolidated entities	$ 250,000,000	0
Junior Subordinated Notes
Debt Instrument [Line Items]
Total outstanding borrowings of unconsolidated entities	75,887,000	74,337,000
Unamortized accretion	24,886,000	26,436,000
Junior Subordinated Notes | Carrying Amount
Debt Instrument [Line Items]
Total financial liabilities	75,887,000	74,337,000
Senior Notes | Carrying Amount
Debt Instrument [Line Items]
Total financial liabilities	$ 948,521,000	$ 903,691,000