Income Taxes - Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income tax computed at statutory rate	$ 57,538	$ 30,182	$ 14,971
State income taxes, net of federal benefit	4,482	1,564	1,300
Deferred rate change	346	(904)	260
Changes in uncertain tax positions	0	0	(2)
Permanent differences	2,952	2,433	2,177
Tax credits	(12,081)	(12,088)	(939)
Other, net	34	359	206
Total expense	$ 53,271	$ 21,546	$ 17,973