Fair Value Measurements - Carrying Values and Estimated Fair Values of Other Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Sep. 30, 2023
Carrying Amount
Financial assets
Total financial assets	$ 9,174	$ 1,951
Financial liabilities
Notes payable	974,644	978,028
Carrying Amount | Senior Notes
Financial liabilities
Notes payable	899,791	903,691
Carrying Amount | Junior Subordinated Notes
Financial liabilities
Notes payable	74,853	74,337
Fair Value
Financial assets
Total financial assets	9,185	1,986
Financial liabilities
Notes payable	976,629	932,865
Fair Value | Senior Notes
Financial liabilities
Notes payable	901,776	858,528
Fair Value | Junior Subordinated Notes
Financial liabilities
Notes payable	$ 74,853	$ 74,337