Borrowings - Narrative (Details) - USD ($) $ in Thousands			1 Months Ended	12 Months Ended
	Jun. 01, 2022	Jun. 01, 2012	Jan. 31, 2010	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023	Jan. 28, 2025	Jan. 27, 2025
Debt Instrument [Line Items]
Debt repurchased				$ 0
Loss on extinguishment of debt				0	$ 437	$ 546
6 3/4% Senior Notes Maturing March of 2025 | Senior Notes
Debt Instrument [Line Items]
Extinguishment of debt					202,200	9,000
Loss on extinguishment of debt					400	$ 100
Junior Subordinated Notes
Debt Instrument [Line Items]
Aggregate principle balance of notes				$ 100,800
Weighted average fixed interest rate of debt				7.02%
Unamortized discount				$ 22,300
Junior Subordinated Debt, Modified Terms
Debt Instrument [Line Items]
Aggregate principal amount of debt			$ 75,000
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
Basis spread on variable rate			2.71%
Senior Unsecured Revolving Credit Facility
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity				400,000
Credit facility, available increase in borrowing capacity				35,000
Line of credit				0	0
Letters of credit secured using cash collateral				41,400
Amount of available borrowings under the secured revolving credit facility				323,600
Senior Unsecured Revolving Credit Facility | Senior Notes
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity				365,000			$ 365,000	$ 300,000
Letter of Credit
Debt Instrument [Line Items]
Letters of credit secured using cash collateral				0	$ 36,400
Letter of Credit | Senior Notes
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity				$ 100,000