Pension Benefits (Net Periodic Pension Cost) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2021	Jan. 31, 2020	Jan. 31, 2021	Jan. 31, 2020
Pension and Other Postretirement Benefits Cost (Reversal of Cost) [Abstract]
Interest cost	$ 1,165	$ 1,493	$ 3,496	$ 4,480
Expected return on plan assets	(2,107)	(2,082)	(6,322)	(6,245)
Recognized net actuarial loss	441	423	1,321	1,269
Net periodic pension benefit	$ (501)	$ (166)	$ (1,505)	$ (496)