Pension Benefits (Net Periodic Pension Cost) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2017	Jan. 31, 2016
Pension and Other Postretirement Benefit Expense [Abstract]
Interest cost	$ 1,443	$ 1,754	$ 4,329	$ 5,260
Expected return on plan assets	(2,019)	(2,036)	(6,059)	(6,106)
Recognized net actuarial loss	442	353	1,328	1,059
Net periodic pension (benefit) cost	$ (134)	$ 71	$ (402)	$ 213