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Income Taxes - Additional Information (Details) - USD ($)
$ in Thousands
12 Months Ended
Apr. 30, 2020
Apr. 30, 2019
Apr. 30, 2018
Income Tax Disclosure [Line Items]      
Federal statutory income tax rate   30.30%  
Effective income tax rate 1.00% 11.00% 23.00%
Tax benefits realized from the recognition of stock option deductions $ 878 $ 298 $ 186
Unrecognized tax benefits that, if recognized, would impact effective tax rate 34 43 56
Liability for potential penalties and interest 19 22  
Research and development state tax credits 703 678 493
Benefit from impact of changes in tax rate 0 0 1,206
State and Local Jurisdiction      
Income Tax Disclosure [Line Items]      
Operating loss carryforwards $ 5,700    
Operating loss carryforwards expiration year 2035    
Research and development state tax credits $ 427 $ 488 $ 290