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Income Taxes - Additional Information (Detail) - USD ($)
 12 Months Ended
Apr. 30, 2019
Apr. 30, 2018
Income Taxes [Line Items]    
Deferred income tax expense $ 75,000  
Tax expense related to GILTI 265,000  
State loss carryforward 26,000  
State tax credit carry forward 207,000  
Valuation allowance, potential expiration of tax credits 37,000  
Federal research and development tax credit carryforward 228,000  
Foreign tax credit carryforwards 638,321 $ 0
Gross net operating losses 1,126,000  
Gross net operating losses outside of United States, amount expiring 501,000  
Additional valuation allowance $ 7,000  
Minimum    
Income Taxes [Line Items]    
Federal, state and local tax returns period 3 years  
Foreign subsidiaries tax returns period 3 years  
Maximum    
Income Taxes [Line Items]    
Federal, state and local tax returns period 4 years  
Foreign subsidiaries tax returns period 7 years