Income Taxes - Components of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Current federal	$ (4,641)	$ (4,935)	$ 57
Current state	485	693	512
Deferred federal	20,639	(31,291)	102,082
Deferred state	1,490	(1,684)	(8,167)
Total expense (benefit)	$ 17,973	$ (37,217)	$ 94,484