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Disclosure of Compensation Related Costs, Share Based Payments (Details) - USD ($)
9 Months Ended
Jan. 31, 2020
Jan. 31, 2019
Apr. 30, 2019
Employee Stock Option      
Share-based Compensation Arrangement by Share-based Payment Award      
Number of shares available for grant reduction per stock option issued (in shares) 1    
Restricted Stock Units      
Share-based Compensation Arrangement by Share-based Payment Award      
Number of shares available for grant reduction per equity instruments other options issued (in shares) 2    
Stock Incentive Plans      
Share-based Compensation Arrangement by Share-based Payment Award      
Allocated share-based compensation expense $ 14,394,000 $ 13,719,000  
Stock Incentive Plans | Employee Stock Option      
Share-based Compensation Arrangement by Share-based Payment Award      
Unrecognized compensation costs related to plan 0    
Stock Incentive Plans | Restricted Stock Units      
Share-based Compensation Arrangement by Share-based Payment Award      
Unrecognized compensation costs related to plan $ 20,236,000    
Return on invested capital measurement period 3 years    
Prior Plans | Employee Stock Option      
Share-based Compensation Arrangement by Share-based Payment Award      
Number of options outstanding (in shares) 55,941   109,827
Aggregate intrinsic value for outstanding options $ 6,515,000    
Weighted average remaining contractual life (in years) 1 year 5 months 1 day    
Aggregate intrinsic value for exercised options $ 5,860,000    
2018 Stock Plan      
Share-based Compensation Arrangement by Share-based Payment Award      
Number of shares available for grant (in shares) 2,614,568    
2018 Stock Plan | Employee Stock Option      
Share-based Compensation Arrangement by Share-based Payment Award      
Number of options outstanding (in shares) 0