Borrowings - Narrative (Details) - USD ($)			1 Months Ended	9 Months Ended	12 Months Ended
	Jun. 01, 2022	Jun. 01, 2012	Jan. 31, 2010	Jun. 30, 2024	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022	Mar. 31, 2024
Debt Instrument [Line Items]
Gain (loss) on extinguishment of debt					$ (437,000)	$ (546,000)	$ 309,000
Senior Notes
Debt Instrument [Line Items]
Gain (loss) on extinguishment of debt							300,000
7.500% Senior Notes (2031 Notes) | Senior Notes
Debt Instrument [Line Items]
Aggregate principal amount of debt								$ 250,000,000
6.750% Senior Notes (2025 Notes) | Senior Notes
Debt Instrument [Line Items]
Extinguishment of debt					4,300,000	9,000,000	18,400,000
Redemption of debt					197,900,000
Gain (loss) on extinguishment of debt					(400,000)	(100,000)
5.875% Senior Notes (2027 Notes) | Senior Notes
Debt Instrument [Line Items]
Extinguishment of debt							$ 6,000,000
Junior Subordinated Notes
Debt Instrument [Line Items]
Aggregate principle balance of notes					$ 100,800,000
Weighted average fixed interest rate of debt					7.97%
Unamortized discount					$ 24,400,000
Junior Subordinated Debt, Modified Terms
Debt Instrument [Line Items]
Aggregate principal amount of debt			$ 75,000,000.0
Variable rate floor			4.25%
Variable rate cap			9.25%
Redemption price percentage		75.00%
Annual increase of percentage of principal amount redeemable	1.785%
Junior Subordinated Debt, Original Terms
Debt Instrument [Line Items]
Aggregate principal amount of debt					25,800,000
Basis spread on variable rate			2.71%	2.45%
Revolving Credit Facility
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity					400,000,000
Credit facility, available increase in borrowing capacity					100,000,000
Line of credit					0	0
Letters of credit secured using cash collateral					0
Amount of available borrowings under the secured revolving credit facility					300,000,000.0
Revolving Credit Facility | Senior Notes
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity					300,000,000
Letter of Credit
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity					100,000,000.0
Letters of credit secured using cash collateral					$ 36,400,000	$ 31,200,000