Fair Value Measurements - Carrying Values and Estimated Fair Values of Other Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Sep. 30, 2023
Carrying Amount
Financial assets
Total financial assets	$ 9,279	$ 1,951
Financial liabilities
Total financial liabilities	1,023,311	978,028
Carrying Amount | Senior Notes
Financial liabilities
Total financial liabilities	947,941	903,691
Carrying Amount | Junior Subordinated Notes
Financial liabilities
Total financial liabilities	75,370	74,337
Fair Value
Financial assets
Total financial assets	9,579	1,986
Financial liabilities
Total financial liabilities	1,034,350	932,865
Fair Value | Senior Notes
Financial liabilities
Total financial liabilities	958,980	858,528
Fair Value | Junior Subordinated Notes
Financial liabilities
Total financial liabilities	$ 75,370	$ 74,337