Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Income Tax Disclosure [Abstract]
Tax at statutory rate	$ 259,513	$ 209,925	$ 178,901
Common stock dividends deductible for tax reporting	(1,354)	(1,355)	(1,355)
State taxes (net of federal benefit)	29,130	25,129	24,669
Amortization of excess deferred taxes	(100,271)	(123,953)	(127,193)
Other, net	5,863	4,033	2,488
Income tax expense	$ 192,881	$ 113,779	$ 77,510