Pension Benefits (Net Periodic Pension Cost) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2016	Jan. 31, 2015	Jan. 31, 2016	Jan. 31, 2015
Pension and Other Postretirement Benefit Expense [Abstract]
Interest cost	$ 1,754	$ 1,617	$ 5,260	$ 4,850
Expected return on plan assets	(2,036)	(1,917)	(6,106)	(5,750)
Recognized net actuarial loss	353	216	1,059	649
Net periodic pension (benefit) cost	$ 71	$ (84)	$ 213	$ (251)