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Income Taxes - Additional Information (Details) - USD ($)
12 Months Ended
Apr. 30, 2019
Apr. 30, 2018
Apr. 30, 2017
Income Tax Disclosure [Line Items]      
Federal statutory income tax rate   30.30%  
Effective income tax rate 11.00% 23.00% 32.00%
Tax benefits realized from the recognition of stock option deductions $ 298,000 $ 186,000 $ 253,000
Unrecognized tax benefits that, if recognized, would impact effective tax rate 43,000 56,000 57,000
Liability for potential penalties and interest 22,000 24,000  
Research and development state tax credits 678,000 493,000 520,000
Benefit from impact of changes in tax rate 0 1,206,000 $ 0
State and Local Jurisdiction      
Income Tax Disclosure [Line Items]      
Operating loss carryforwards $ 5,400,000    
Operating loss carryforwards expiration year 2035    
Research and development state tax credits $ 488,000 $ 290,000