Pension Benefits (Net Periodic Pension Cost) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2019	Oct. 31, 2018
Pension and Other Postretirement Benefits Cost (Reversal of Cost) [Abstract]
Interest cost	$ 1,494	$ 1,568	$ 2,987	$ 3,135
Expected return on plan assets	(2,082)	(2,128)	(4,163)	(4,255)
Recognized net actuarial loss	423	412	846	824
Net periodic pension benefit	$ (165)	$ (148)	$ (330)	$ (296)