Pension Benefits (Net Periodic Pension Cost) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017
Pension and Other Postretirement Benefit Expense [Abstract]
Interest cost	$ 1,431	$ 1,443	$ 4,295	$ 4,329
Expected return on plan assets	(2,234)	(2,019)	(6,702)	(6,059)
Recognized net actuarial loss	401	442	1,201	1,328
Net periodic pension benefit	$ (402)	$ (134)	$ (1,206)	$ (402)