Income Taxes - Reconciliation of the Federal Statutory Tax Rate to the Total Tax Provision (Benefit) (Detail)	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Federal income taxes computed at the statutory rate	21.00%	21.00%
State income taxes, net of federal benefit	11.80%	1.60%
Research & development tax refunds & credits	28.80%	(5.10%)
Dividend received deduction	6.40%	(1.90%)
Other, net	10.00%	(3.10%)
Effective income tax rate	78.00%	12.50%