Note 8 - Federal, State and Local Income Taxes - Effective Income Tax Rate Reconciliation (Details)	9 Months Ended
	Jan. 31, 2018	Jan. 31, 2017
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	30.33%	35.00%
Effect on deferred tax liabilities from federal tax rate reduction to 21%	(65.87%)
State and local income taxes, net of federal income tax benefit	1.27%	(0.39%)
Effect of dividends received deductions	(0.47%)	(0.29%)
Domestic production tax credit	(0.13%)	(0.19%)
Other, net	0.18%	(0.65%)
Effective income tax rate	(34.69%)	33.48%