Pension Benefits (Net Periodic Pension Cost) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Oct. 31, 2012	Oct. 31, 2011	Oct. 31, 2012	Oct. 31, 2011
Pension Benefits [Abstract]
Service cost	$ 0	$ 1,283	$ 0	$ 2,566
Interest cost	1,565	1,677	3,130	3,353
Expected return on plan assets	(1,641)	(1,656)	(3,282)	(3,312)
Amortization of net loss	231	522	462	1,044
Amortization of prior service cost	0	20	0	40
Net periodic pension cost	$ 155	$ 1,846	$ 310	$ 3,691