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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, 2017
$ / shares
shares
Number of option shares  
Outstanding at the beginning of the period (in shares) | shares 222,050
Granted (in shares) | shares 0
Exercised (in shares) | shares 10,225
Forfeited (in shares) | shares 0
Outstanding at the end of the period (in shares) | shares 211,825
Weighted average option exercise price  
Outstanding at the beginning of the period (in dollars per share) | $ / shares $ 38.51
Granted (in dollars per share) | $ / shares 0.00
Exercised (in dollars per share) | $ / shares 29.10
Forfeited (in dollars per share) | $ / shares 0.00
Outstanding at the end of the period (in dollars per share) | $ / shares $ 38.96