Note 8 - Federal, State and Local Income Taxes - Effective Income Tax Rate Reconciliation (Details)	3 Months Ended		12 Months Ended
	Jul. 31, 2018	Jul. 31, 2017	Apr. 30, 2017
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	35.00%	35.00%
State and local income taxes, net of federal income tax benefit	(5.70%)	0.73%
Effect of dividends received deductions	(0.27%)	(0.37%)
Domestic production tax credit		0.65%
Other, net	0.04%	0.09%
Effective income tax rate	15.07%	34.80%