Note 8 - Federal, State and Local Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details)	9 Months Ended
	Jan. 31, 2017	Jan. 31, 2016
U.S. statutory federal tax rate	35.00%	35.00%
State and local income taxes, net of federal income tax benefit	0.39%	1.38%
Effect of dividends received deductions	0.29%	0.70%
Domestic production tax credit	0.19%	0.54%
Settlement of tax audits		3.60%
Other, net	0.65%
Effective income tax rate	33.48%	28.78%