Borrowings - Schedule of Long-term Debt (Details) - USD ($)	Dec. 31, 2023	Sep. 30, 2023	Sep. 30, 2019	Oct. 31, 2017	Mar. 31, 2017
Debt Instrument [Line Items]
Total outstanding borrowings of unconsolidated entities	$ 974,644,000	$ 978,028,000
Unamortized debt issuance costs	(5,379,000)	(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	899,791,000	903,691,000
Unamortized debt issuance costs	$ (5,379,000)	(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	$ 197,915,000	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
Junior Subordinated Notes
Debt Instrument [Line Items]
Total outstanding borrowings of unconsolidated entities	74,853,000	74,337,000
Unamortized accretion	$ 25,920,000	$ 26,436,000