Pension Benefits (Net Periodic Pension Cost) (Details) - USD ($) $ in Thousands	3 Months Ended
	Jul. 31, 2016	Jul. 31, 2015
Pension and Other Postretirement Benefit Expense [Abstract]
Interest cost	$ 1,443	$ 1,754
Expected return on plan assets	(2,020)	(2,036)
Recognized net actuarial loss	443	353
Net periodic pension (benefit) cost	$ (134)	$ 71