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Stock-Based Compensation (Schedule Of Stock Options Oustanding Activity) (Details)
12 Months Ended
Apr. 30, 2017
$ / shares
shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Options outstanding | shares 54,918
Options exercisable | shares 17,949
$22.77 - $23.96 [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Option price per share, lower range limit $ 22.77
Option price per share, upper range limit $ 23.96
Options outstanding | shares 11,750
Options outstanding remaining life 1 year 2 months 12 days
Options outstanding exercise price $ 23.45
Options exercisable | shares 11,750
Options exercisable exercise price $ 23.45
$29.92- $34.11 [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Option price per share, lower range limit 29.92
Option price per share, upper range limit $ 34.11
Options outstanding | shares 24,533
Options outstanding remaining life 5 years 8 months 12 days
Options outstanding exercise price $ 30.34
Options exercisable | shares 4,966
Options exercisable exercise price $ 32.02
$57.11 [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Option price per share, lower range limit 57.11
Option price per share, upper range limit $ 57.11
Options outstanding | shares 18,635
Options outstanding remaining life 8 years 1 month 6 days
Options outstanding exercise price $ 57.11
Options exercisable | shares 1,233
Options exercisable exercise price $ 57.11