Income Taxes - Schedule of Income Tax Reconciliation by Applying Federal Income Tax Rate (Details) - USD ($) $ in Thousands		12 Months Ended
		Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Income Tax Disclosure [Abstract]
U.S. Income Before Income Taxes		$ 87,255	$ 641,399	$ 682,650
Income Tax Expense, Computed at U.S. Federal Statutory Rate of 21%		18,324	134,694	143,357
State Valuation Allowance	[1]	0	0	(24,850)
State Income Taxes	[2]	1,892	36,331	8,736
Amortization of Excess Deferred Federal Income Taxes		(5,607)	(6,053)	(5,184)
Plant Flow Through Items		(6,135)	(2,856)	(814)
Stock Compensation		1,758	957	820
Federal Tax Credits		(5)	(6)	(5,701)
Miscellaneous		(485)	1,466	265
Total Income Taxes		$ 9,742	$ 164,533	$ 116,629
Federal Statutory Rate		21.00%	21.00%	21.00%

[1] During fiscal 2022, the valuation allowance recorded against certain state deferred tax assets was removed. See discussion below.

[2] The state income tax expense shown above includes adjustments to the estimated state effective tax rates utilized in the calculation of deferred income taxes, including the Pennsylvania rate change discussed above.