Pension Benefits (Net Periodic Pension Cost) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2015	Oct. 31, 2014	Oct. 31, 2015	Oct. 31, 2014
Pension and Other Postretirement Benefit Expense [Abstract]
Interest cost	$ 1,753	$ 1,617	$ 3,507	$ 3,233
Expected return on plan assets	(2,035)	(1,917)	(4,071)	(3,833)
Recognized net actuarial loss	353	216	706	433
Net periodic pension (benefit) cost	$ 71	$ (84)	$ 142	$ (167)