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Stock-Based Compensation (Narrative) (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Oct. 31, 2019
Oct. 31, 2018
Oct. 31, 2019
Oct. 31, 2018
Apr. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Stock-based compensation expense $ 1,178 $ 836 $ 2,075 $ 1,622  
Liability for payment of the RSTUs $ 50,528   $ 50,528   $ 54,906
Employee Service-Based RSUs [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Awarded in period (shares) 9,600   33,091    
Vesting period     2 years    
Employee Performance-Based RSUs [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Awarded in period (shares)     61,379    
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)     6,483    
Employee Service-Based RSTUs [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Restricted stock units non vested grants (shares)     3,482    
RSTUs [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Vesting period, years     3 years    
Stock-based compensation expense $ 200 $ (100) $ 200 $ 200  
Liability for payment of the RSTUs $ 600   $ 600   $ 700
Cliff Vest [Member] | RSUs [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Vesting period, years     3 years