Note 7 - Federal, State and Local Income Taxes - Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2017
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	30.33%	35.00%
Effect on deferred tax liabilities from federal tax rate reduction to 21%		(54.51%)
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent	6.02%	0.70%	(0.88%)
Effect of dividends received deductions	(0.24%)	(0.49%)	(0.33%)
Domestic production tax credit			(0.17%)
Other, net	0.03%	0.10%	(0.57%)
Effective income tax rate	26.81%	(23.87%)	33.05%