Pension Benefits (Net Periodic Pension Cost) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2016	Oct. 31, 2015	Oct. 31, 2016	Oct. 31, 2015
Pension and Other Postretirement Benefit Expense [Abstract]
Interest cost	$ 1,443	$ 1,753	$ 2,886	$ 3,507
Expected return on plan assets	(2,019)	(2,035)	(4,039)	(4,071)
Recognized net actuarial loss	442	353	885	706
Net periodic pension (benefit) cost	$ (134)	$ 71	$ (268)	$ 142