Defined Benefit Retirement Plans (Details) (USD $)	3 Months Ended
	Jul. 31, 2012	Jul. 31, 2011
Defined benefit plans, net periodic benefit cost [Abstract]
Service Cost	$ 4,566,000	$ 4,210,000
Interest Cost	6,867,000	7,027,000
Expected Return on Plan Assets	(7,714,000)	(7,358,000)
Net Amortization of Prior Service Cost	245,000	224,000
Recognized Net Actuarial Loss	2,327,000	1,256,000
Net Pension Expense	6,291,000	5,359,000
Pension plan contributions	$ 2,800,000	$ 2,400,000