Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Oct. 31, 2011	Oct. 31, 2010	Oct. 31, 2011	Oct. 31, 2010
Components of comprehensive income
Net income	$ 127,247	$ 149,726	$ 238,770	$ 252,607
Other comprehensive (loss) income:
Foreign currency translation adjustments	(14,892)	2,542	(18,213)	(1,066)
Unrealized (loss) gain on available-for-sale securities	(1,623)	1,361	(1,829)	(36)
Unrealized (loss) gain on cash flow hedging derivatives, net	(10,004)	(2,226)	(22,126)	6,742
Unrealized loss on pension and other postretirement liabilities	0	0	0	(300)
Income tax benefit (expense)	4,206	317	8,688	(2,546)
Comprehensive income	$ 104,934	$ 151,720	$ 205,290	$ 255,401