Pension Benefits (Net Periodic Pension Cost) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2019	Jan. 31, 2018
Pension and Other Postretirement Benefits Cost (Reversal of Cost) [Abstract]
Interest cost	$ 1,567	$ 1,431	$ 4,702	$ 4,295
Expected return on plan assets	(2,127)	(2,234)	(6,382)	(6,702)
Recognized net actuarial loss	412	401	1,236	1,201
Net periodic pension benefit	$ (148)	$ (402)	$ (444)	$ (1,206)