Disclosure of Compensation Related Costs, Share Based Payments - Schedule of Stock Option Activity (Details) - 2009 Stock Incentive Plan - Employee Stock Option	9 Months Ended
	Jan. 31, 2017 $ / shares shares
Number of option shares
Outstanding at the beginning of the period (in shares) | shares	291,200
Granted (in shares) | shares	0
Exercised (in shares) | shares	57,700
Forfeited (in shares) | shares	0
Outstanding at the end of the period (in shares) | shares	233,500
Weighted average option exercise price
Outstanding at the beginning of the period (in dollars per share) | $ / shares	$ 37.46
Granted (in dollars per share) | $ / shares	0.00
Exercised (in dollars per share) | $ / shares	34.22
Forfeited (in dollars per share) | $ / shares	0.00
Outstanding at the end of the period (in dollars per share) | $ / shares	$ 38.26