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Preferred and Common Stock (Details) - USD ($)
3 Months Ended 12 Months Ended 14 Months Ended
Apr. 30, 2018
Apr. 30, 2018
Apr. 30, 2017
Apr. 30, 2016
Apr. 30, 2018
Apr. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award            
Shares issued of preferred stock (shares) 0 0 0   0  
Options outstanding (shares) 181,673 181,673     181,673  
Aggregate intrinsic value of outstanding options $ 10,376,000 $ 10,376,000     $ 10,376,000  
Aggregate intrinsic value of exercised options   $ 3,144,000        
Exercise price range floor (in Dollars per share)   $ 25.26        
Exercise price range ceiling (in Dollars per share)   $ 44.39        
Repurchase of common stock   $ 215,434,000 $ 49,374,000      
Stock Options            
Share-based Compensation Arrangement by Share-based Payment Award            
Reduction in available shares per stock option issued (shares) 1 1     1  
Options outstanding (shares) 181,673 181,673 222,050 291,200 181,673 401,800
Weighted average remaining contractual life (years)   2 years 7 months 24 days        
Restricted Stock            
Share-based Compensation Arrangement by Share-based Payment Award            
Reduction in available shares per restricted stock or restricted stock unit issued (shares) 2 2     2  
Restricted Stock Units            
Share-based Compensation Arrangement by Share-based Payment Award            
Reduction in available shares per restricted stock or restricted stock unit issued (shares) 2 2     2  
Stock Options, Restricted Stock and Restricted Stock Units            
Share-based Compensation Arrangement by Share-based Payment Award            
Share-based compensation expense   $ 17,880,000 $ 10,697,000 $ 7,413,000    
2009 Stock Incentive Plan            
Share-based Compensation Arrangement by Share-based Payment Award            
Shares available for grant under the Plan (shares) 2,984,804 2,984,804     2,984,804  
Unrecognized compensation costs $ 9,058,000 $ 9,058,000     $ 9,058,000  
2017 Stock Repurchase Plan            
Share-based Compensation Arrangement by Share-based Payment Award            
Share repurchase program authorized amount     $ 300,000,000      
Share repurchase program period in force   2 years        
Common stock shares repurchased (shares)         2,441,600  
Repurchase of common stock         $ 264,800,000  
Remaining authorized repurchase amount 35,200,000 $ 35,200,000     35,200,000  
2018 Stock Repurchase Plan            
Share-based Compensation Arrangement by Share-based Payment Award            
Share repurchase program authorized amount 300,000,000 $ 300,000,000     $ 300,000,000  
Repurchase of common stock $ 0          
Preferred Stock            
Share-based Compensation Arrangement by Share-based Payment Award            
Authorized shares of preferred stock (shares) 1,000,000 1,000,000     1,000,000  
Shares issued of preferred stock (shares) 0 0     0  
Series A Preferred Stock            
Share-based Compensation Arrangement by Share-based Payment Award            
Authorized shares of preferred stock (shares) 250,000 250,000     250,000  
Common Stock            
Share-based Compensation Arrangement by Share-based Payment Award            
Authorized shares of common stock (shares) 120,000,000 120,000,000     120,000,000