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Note 8 - Federal, State and Local Income Taxes (Details Textual)
3 Months Ended 12 Months Ended
Jul. 31, 2018
Jul. 31, 2017
Apr. 30, 2019
Apr. 30, 2018
Apr. 30, 2017
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent 21.00% 35.00%     35.00%
Effective Income Tax Rate Reconciliation, Percent, Total 15.07% 34.80%      
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent       (54.51%)  
Earliest Tax Year [Member]          
Open Tax Year 2014        
Latest Tax Year [Member]          
Open Tax Year 2017        
Scenario, Forecast [Member]          
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent     21.00%