Pension Benefits (Net Periodic Pension Cost) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2018	Oct. 31, 2017
Pension and Other Postretirement Benefits Cost (Reversal of Cost) [Abstract]
Interest cost	$ 1,568	$ 1,432	$ 3,135	$ 2,864
Expected return on plan assets	(2,128)	(2,234)	(4,255)	(4,468)
Recognized net actuarial loss	412	400	824	800
Net periodic pension benefit	$ (148)	$ (402)	$ (296)	$ (804)