Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income tax percentage (as a percent)			24.50%
Income tax expense computed at the statutory rate	$ (148,327)	$ 45,275	$ 56,915
State income taxes, net of federal benefit	(3,521)	7,855	8,795
Tax exempt interest income	(5,515)	(5,193)	(5,778)
Tax impact of stock-based compensation plans	83	(91)	(424)
Tax impact of goodwill impairment	131,051	0	0
Impact of enacted federal income tax rate reduction	0	0	13,709
Other	719	384	902
Total (benefit from) provision for income taxes	$ (25,510)	$ 48,230	$ 74,119