Pension Benefits (Net Periodic Pension Cost) (Details) - USD ($) $ in Thousands	3 Months Ended
	Jul. 31, 2017	Jul. 31, 2016
Pension and Other Postretirement Benefit Expense [Abstract]
Interest cost	$ 1,432	$ 1,443
Expected return on plan assets	(2,234)	(2,020)
Recognized net actuarial loss	400	443
Net periodic pension (benefit) cost	$ (402)	$ (134)