Income Taxes - Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income tax computed at statutory rate	$ 38,356	$ 57,538	$ 30,182
State income taxes, net of federal benefit	2,874	4,482	1,564
Deferred rate change	665	346	(904)
Permanent differences	2,216	2,952	2,433
Tax credits	(20,287)	(12,081)	(12,088)
Other, net	134	34	359
Total expense from income taxes	$ 23,958	$ 53,271	$ 21,546