Borrowings - Schedule of Long-term Debt (Details) - USD ($)	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	Oct. 31, 2022	Oct. 13, 2022
Debt Instrument [Line Items]
Unamortized debt issuance costs	$ (5,759,000)	$ (7,280,000)
Total debt, net	978,028,000	983,440,000
Gain (Loss) on extinguishment of debt	(546,000)	309,000	$ (2,025,000)
Revolving Credit Facility
Debt Instrument [Line Items]
Secured Revolving Credit Facility	0	0
Credit facility, maximum borrowing capacity				$ 250,000,000	$ 265,000,000
Gain (Loss) on extinguishment of debt	500,000
Letters of credit secured using cash collateral	0	5,500,000
Line of credit facility, remaining borrowing capacity	265,000,000	244,500,000
Senior Notes
Debt Instrument [Line Items]
Unamortized debt issuance costs	(5,759,000)	(7,280,000)
Total debt, net	903,691,000	911,170,000
Junior Subordinated Notes
Debt Instrument [Line Items]
Total debt, net	74,337,000	72,270,000
Unamortized discount	26,436,000	28,503,000
6.750% Senior Notes (2025 Notes) | Senior Notes
Debt Instrument [Line Items]
Total debt, net	$ 202,195,000	$ 211,195,000
Stated interest rate on debt instrument	6.75%	6.75%
5.875% Senior Notes (2027 Notes) | Senior Notes
Debt Instrument [Line Items]
Total debt, net	$ 357,255,000	$ 357,255,000
Stated interest rate on debt instrument	5.875%	5.875%
7.250% Senior Notes (2029 Notes) | Senior Notes
Debt Instrument [Line Items]
Total debt, net	$ 350,000,000	$ 350,000,000
Stated interest rate on debt instrument	7.25%	7.25%
Senior Notes
Debt Instrument [Line Items]
Gain (Loss) on extinguishment of debt		$ (300,000)
Senior Notes | 6.750% Senior Notes (2025 Notes)
Debt Instrument [Line Items]
Gain (Loss) on extinguishment of debt	$ 100,000
Senior Notes | 5.875% Senior Notes (2027 Notes)
Debt Instrument [Line Items]
Gain (Loss) on extinguishment of debt			$ 2,000,000
Junior Subordinated Notes
Debt Instrument [Line Items]
Unamortized discount	$ 26,400,000