Income Taxes - Schedule of Income Tax Reconciliation by Applying Federal Income Tax Rate (Details) - USD ($) $ in Thousands		12 Months Ended
		Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Income Tax Disclosure [Abstract]
U.S. Income Before Income Taxes		$ 694,053	$ 87,255	$ 641,399
Income Tax Expense, Computed at U.S. Federal Statutory Rate of 21%		145,751	18,324	134,694
State Income Taxes		33,637	1,892	36,331
Amortization of Excess Deferred Federal Income Taxes		(4,617)	(5,607)	(6,053)
Plant Flow Through Items		(5,070)	(6,135)	(2,856)
Stock Compensation		2,245	1,758	957
Miscellaneous		3,603	(490)	1,460
Total Income Taxes	[1]	$ 175,549	$ 9,742	$ 164,533
Federal Statutory Rate		21.00%	21.00%	21.00%

[1] The Company considers this line to be a significant expense.