Note 7 - Federal, State and Local Income Taxes - Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	30.33%	35.00%	35.00%
Effect on deferred tax liabilities from federal tax rate reduction to 21%	(54.51%)
State and local income taxes, net of federal income tax benefit	0.70%	(0.88%)	(3.39%)
Effect of dividends received deductions	(0.49%)	(0.33%)	(0.41%)
Domestic production tax credit		(0.17%)	(0.33%)
Other, net	0.10%	(0.57%)	(3.72%)
Effective income tax rate	(23.87%)	33.05%	27.15%