Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Tax at statutory rate	$ 149,730	$ 211,433	$ 189,764
Common stock dividends deductible for tax reporting	(1,745)	(2,584)	(2,570)
State taxes (net of federal benefit)	19,826	16,100	11,133
Change in valuation allowance	0	0	1,324
Amortization of excess deferred taxes	(1,219)	0	0
Remeasurement due to TCJA	(158,782)	0	0
Other, net	270	(3,566)	(3,009)
Income tax expense (benefit)	$ 8,080	$ 221,383	$ 196,642
Statutory federal income tax rate	24.50%	35.00%	35.00%