Borrowings - Schedule of Long-term Debt (Details) - USD ($)	Mar. 31, 2024	Sep. 30, 2023
Debt Instrument [Line Items]
Total outstanding borrowings of unconsolidated entities	$ 1,023,311,000	$ 978,028,000
Unamortized debt issuance costs	(9,314,000)	(5,759,000)
Senior Unsecured Revolving Credit Facility
Debt Instrument [Line Items]
Senior Unsecured Revolving Credit Facility	0	0
Senior Notes
Debt Instrument [Line Items]
Total outstanding borrowings of unconsolidated entities	947,941,000	903,691,000
Unamortized debt issuance costs	$ (9,314,000)	$ (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	75,370,000	74,337,000
Unamortized accretion	$ 25,403,000	$ 26,436,000