Fair Value Measurements - Schedule of Carrying Values and Estimated Fair Values of Other Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Sep. 30, 2024
Carrying Amount
Financial assets
Total financial assets	$ 0	$ 9,449
Financial liabilities
Total financial liabilities	1,029,114	1,025,349
Carrying Amount | Senior Notes
Financial liabilities
Notes	950,644	948,945
Carrying Amount | Junior Subordinated Notes
Financial liabilities
Notes	78,470	76,404
Fair Value
Financial assets
Total financial assets	0	9,584
Financial liabilities
Total financial liabilities	1,047,104	1,052,898
Fair Value | Senior Notes
Financial liabilities
Notes	968,634	976,494
Fair Value | Junior Subordinated Notes
Financial liabilities
Notes	78,470	76,404
Certificates of Deposit | Carrying Amount
Financial assets
Certificates of deposit	0	9,449
Certificates of Deposit | Fair Value
Financial assets
Certificates of deposit	$ 0	$ 9,584