Income Taxes - Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Federal:
Current	$ 53,820	$ 49,782	$ 46,376
Deferred	(8,468)	(7,858)	1,916
Federal	45,352	41,924	48,292
State:
Current	5,584	5,310	4,557
Deferred	(1,413)	(1,486)	(330)
Deferred	4,171	3,824	4,227
Total
Current	59,404	55,092	50,933
Deferred	(9,881)	(9,344)	1,586
Income tax expense	$ 49,523	$ 45,748	$ 52,519

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