Disclosure of Compensation Related Costs, Share Based Payments - Schedule of Stock Option Activity (Details) - 2009 Stock Incentive Plan - Employee Stock Option	3 Months Ended
	Jul. 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	7,050
Forfeited (in shares) | shares	0
Outstanding at the end of the period (in shares) | shares	215,000
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	27.64
Forfeited (in dollars per share) | $ / shares	0.00
Outstanding at the end of the period (in dollars per share) | $ / shares	$ 38.86