Note 8 - Federal, State and Local Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details)	3 Months Ended
	Jul. 31, 2017	Jul. 31, 2016
U.S. statutory federal tax rate	35.00%	35.00%
State and local income taxes, net of federal income tax benefit	0.73%	1.99%
Effect of dividends received deductions	(0.37%)	(0.06%)
Domestic production tax credit	(0.65%)	0.00%
Other, net	0.09%	0.03%
Effective Income Tax Rate Reconciliation, Percent	34.80%	36.96%