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Stock-Based Compensation (Narrative) (Details) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended
Jul. 31, 2015
Jul. 31, 2014
Apr. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Granted non-statutory stock options to key employees 30,700    
Non-statutory stock options, weighted average exercise price $ 57.11    
Vesting period, years 3 years    
Contractual terms, years 10 years    
Stock-based compensation expense $ 963 $ 943  
Liability for payment of the RSTUs $ 27,172   $ 30,120
Employee Performance Based Restricted Stock Units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Awarded in period 48,201    
Common stock issuable per RSU granted 1    
Employee And Non Employee Director Service Based Restricted Stock Units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Awarded in period 16,049    
Common stock issuable per RSU granted 1    
Restricted Stock Units (RSUs) [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period, years 3 years    
Employee Performance Based Restricted Stock Tracking Units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted stock units non vested grants 7,616    
Employee Service Based Restricted Stock Tracking Units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted stock units non vested grants 2,499    
Restricted Stock Tracking Units RSTU [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period, years 3 years    
Stock-based compensation expense $ 281 $ 49  
Liability for payment of the RSTUs $ 701   $ 420