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Stock-Based Compensation (Narrative) (Details) - USD ($)
$ in Thousands
3 Months Ended
Jul. 31, 2021
Jul. 31, 2020
Apr. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense $ 1,177 $ 961  
Liability for payment of the RSTUs $ 48,039   $ 58,577
Employee Service-Based RSUs [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Awarded in period (shares) 30,984    
Employee Performance-Based RSUs [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Awarded in period (shares) 57,476    
Common stock issuable per RSU granted (shares) 1    
Employee Performance-Based RSTUs [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted stock units non vested grants (shares) 5,794    
Employee Service-Based RSTUs [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted stock units non vested grants (shares) 3,096    
RSTUs [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period, years 3 years    
Stock-based compensation expense $ 100 $ 300  
Liability for payment of the RSTUs $ 600   $ 1,000
Cliff Vest [Member] | RSUs [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period, years 3 years