Income Taxes - Significant Components of Deferred Tax Liabilities and Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Sep. 30, 2023
Deferred Tax Liabilities:
Unrealized Hedging Gains	$ 22,433	$ 3,385
Property, Plant and Equipment	1,134,727	1,178,893
Pension and Other Post-Retirement Benefit Costs	59,877	44,358
Other	13,885	21,470
Total Deferred Tax Liabilities	1,230,922	1,248,106
Deferred Tax Assets:
Tax Loss and Credit Carryforwards	(31,111)	(33,744)
Pension and Other Post-Retirement Benefit Costs	(49,622)	(41,843)
Other	(39,024)	(48,349)
Total Deferred Tax Assets	(119,757)	(123,936)
Total Net Deferred Income Taxes	$ 1,111,165	$ 1,124,170