Income Taxes - Reconciliation of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Currently paid or payable
Federal	$ 18,511	$ 30,779	$ 42,261
State	3,733	9,327	10,556
Total	22,244	40,106	52,817
Deferred tax (benefit) expense
Federal	(39,563)	7,507	20,205
State	(8,191)	617	1,097
Total	(47,754)	8,124	21,302
Total (benefit from) provision for income taxes	$ (25,510)	$ 48,230	$ 74,119