Income Taxes - Schedule of Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Current
Federal	$ (10,099)	$ 0	$ 0
State	11,075	9,022	5,667
Deferred
Federal	150,556	197,013	178,630
State	15,330	15,348	12,350
TCJA Impact	(158,782)	0	0
Investment tax credits	0	0	(5)
Income tax expense (benefit)	$ 8,080	$ 221,383	$ 196,642