Income Taxes - Schedule of Income Tax Reconciliation by Applying Federal Income Tax Rate (Details) - USD ($) $ in Thousands		12 Months Ended
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Income Tax Disclosure [Abstract]
U.S. Income Before Income Taxes		$ 641,399	$ 682,650	$ 478,329
Income Tax Expense, Computed at U.S. Federal Statutory Rate of 21%		134,694	143,357	100,449
State Valuation Allowance	[1]	0	(24,850)	(5,560)
State Income Taxes	[2]	36,331	8,736	24,300
Amortization of Excess Deferred Federal Income Taxes		(6,053)	(5,184)	(5,215)
Plant Flow Through Items		(2,856)	(814)	(1,503)
Stock Compensation		957	820	2,239
Federal Tax Credits		(6)	(5,701)	(310)
Miscellaneous		1,466	265	282
Total Income Taxes		$ 164,533	$ 116,629	$ 114,682
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.