Note 3 - Income Taxes - Summary of the Difference Between Statutory Federal Income Tax Rate and Effective Rate (Details)	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Statutory federal income tax rate	21.00%	21.00%
State franchise taxes (net of federal tax benefit)	5.70%	5.20%
Effect of state rate change on beginning balance of deferred tax liabilities	(0.70%)	0.10%
Dividends received deduction	0.40%	(0.20%)
Others	(0.10%)	0.10%
Effective tax rate	26.30%	26.20%