Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Tax at statutory rate	$ 136,565	$ 149,730	$ 211,433
Common stock dividends deductible for tax reporting	(1,460)	(1,745)	(2,584)
State taxes (net of federal benefit)	20,202	19,826	16,100
Amortization of excess deferred taxes	(14,085)	(1,219)	0
TCJA Impact	0	(158,782)	0
Other, net	(2,319)	270	(3,566)
Income tax expense (benefit)	$ 138,903	$ 8,080	$ 221,383
Statutory federal income tax rate	21.00%	24.50%	35.00%