Pension Benefits (Net Periodic Pension Cost) (Details) - USD ($) $ in Thousands	3 Months Ended
	Jul. 31, 2018	Jul. 31, 2017
Pension and Other Postretirement Benefits Cost (Reversal of Cost) [Abstract]
Interest cost	$ 1,567	$ 1,432
Expected return on plan assets	(2,127)	(2,234)
Recognized net actuarial loss	412	400
Net periodic pension benefit	$ (148)	$ (402)