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Stock-Based Compensation (Narrative) (Details) - USD ($)
$ in Thousands
3 Months Ended
Jul. 31, 2018
Jul. 31, 2017
Apr. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense $ 786 $ 945  
Liability for payment of the RSTUs $ 50,423   $ 48,682
Employee Service-Based RSUs [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Awarded in period (in shares) 24,595    
Employee Performance-Based RSUs [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Awarded in period (in shares) 45,615    
Common stock issuable per RSU granted (in shares) 1    
Employee Performance-Based RSTUs [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted stock units non vested grants (in shares) 4,057    
Employee Service-Based RSTUs [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted stock units non vested grants (in shares) 2,243    
RSTUs [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period, years 3 years    
Stock-based compensation expense $ 300 $ 200  
Liability for payment of the RSTUs $ 500   $ 1,000
Cliff Vest [Member] | RSUs [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period, years 3 years