Fair Value Measurements - Schedule of Carrying Values and Estimated Fair Values of Other Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Sep. 30, 2024
Carrying Amount
Financial assets
Total financial assets	$ 412	$ 9,449
Financial liabilities
Total financial liabilities	1,028,173	1,025,349
Carrying Amount | Senior Notes
Financial liabilities
Total financial liabilities	950,219	948,945
Carrying Amount | Junior Subordinated Notes
Financial liabilities
Total financial liabilities	77,954	76,404
Fair Value
Financial assets
Total financial assets	412	9,584
Financial liabilities
Total financial liabilities	1,042,949	1,052,898
Fair Value | Senior Notes
Financial liabilities
Total financial liabilities	964,995	976,494
Fair Value | Junior Subordinated Notes
Financial liabilities
Total financial liabilities	$ 77,954	$ 76,404