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Disclosure of Compensation Related Costs, Share Based Payments - Schedule of Stock Option Activity (Details) - 2009 Stock Incentive Plan - Employee Stock Option
 6 Months Ended
Oct. 31, 2015
$ / shares
shares
Number of Option Shares  
Outstanding at the beginning of the period (in shares) | shares 401,800
Granted (in shares) | shares 0
Exercised (in shares) | shares 59,750
Forfeited (in shares) | shares 0
Outstanding at the end of the period (in shares) | shares 342,050
Weighted Average Option Price  
Outstanding at the beginning of the period (in dollars per share) $ 36.55
Granted (in dollars per share) 0.00
Exercised (in dollars per share) 34.96
Forfeited (in dollars per share) 0.00
Outstanding at the end of the period (in dollars per share) $ 36.83