Note 3 - Income Taxes - Summary of the Difference Between Statutory Federal Income Tax Rate and Effective Rate (Details)	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Statutory federal income tax rate	21.00%	21.00%
State franchise taxes (net of federal tax benefit)	5.00%	5.70%
Effect of state rate change on beginning balance of deferred tax liabilities	(1.00%)	(0.70%)
Dividends received deduction	(1.60%)	0.40%
Others	0.30%	(0.10%)
Effective tax rate	23.70%	26.30%