Asset Retirement Obligations - Reconciliation of Asset Retirement Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	$ 2,417	$ 2,858
Liabilities incurred	0	0
Liabilities settled	0	(502)
Liabilities assumed	0	0
Accretion expense	60	61	$ 100
Balance at end of year	$ 2,477	$ 2,417	$ 2,858