Pensions and Other Postretirement Benefits (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jul. 31, 2012	Jul. 31, 2011
Pensions and Other Postretirement Benefits (Textual) [Abstract]
Reduction in positions due to restructuring	850
Defined Benefit Pension Plans [Member]
Components of net periodic benefit cost
Service cost	$ 2,298	$ 2,062
Interest cost	6,028	6,523
Expected return on plan assets	(6,322)	(6,885)
Recognized net actuarial loss (gain)	3,362	2,201
Settlement loss	6,669	0
Other	254	300
Net periodic benefit cost	12,289	4,201
Other Postretirement Benefits [Member]
Components of net periodic benefit cost
Service cost	673	525
Interest cost	765	780
Expected return on plan assets	0	0
Recognized net actuarial loss (gain)	0	(25)
Settlement loss	0	0
Other	(106)	(100)
Net periodic benefit cost	$ 1,332	$ 1,180