Pension Benefits (Net Periodic Pension Cost) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016
Pension and Other Postretirement Benefit Expense [Abstract]
Interest cost	$ 1,432	$ 1,443	$ 2,864	$ 2,886
Expected return on plan assets	(2,234)	(2,019)	(4,468)	(4,039)
Recognized net actuarial loss	400	442	800	885
Net periodic pension benefit	$ (402)	$ (134)	$ (804)	$ (268)