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, 2016 $ / 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	103,100
Forfeited (in shares) | shares	2,500
Outstanding at the end of the period (in shares) | shares	296,200
Weighted Average Option Price
Outstanding at the beginning of the period (in dollars per share) | $ / shares	$ 36.55
Granted (in dollars per share) | $ / shares	0.00
Exercised (in dollars per share) | $ / shares	34.86
Forfeited (in dollars per share) | $ / shares	25.26
Outstanding at the end of the period (in dollars per share) | $ / shares	$ 37.23