Pension Benefits (Net Periodic Pension Cost) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jul. 31, 2012	Jul. 31, 2011
Pension Benefits [Abstract]
Service cost	$ 0	$ 1,283
Interest cost	1,565	1,676
Expected return on plan assets	(1,641)	(1,656)
Amortization of net loss	231	522
Amortization of prior service cost	0	20
Net periodic pension cost	$ 155	$ 1,845