Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 31, 2012	Jan. 31, 2011	Jan. 31, 2012	Jan. 31, 2011
Components of comprehensive income
Net income	$ 116,844	$ 131,995	$ 355,614	$ 384,602
Other comprehensive (loss) income:
Foreign currency translation adjustments	(459)	6,387	(18,672)	5,321
Unrealized gain (loss) on available-for-sale securities	1,499	794	(330)	758
Unrealized gain (loss) on cash flow hedging derivatives, net	995	(885)	(21,131)	5,857
Unrealized (loss) gain on pension and other postretirement liabilities	(6,270)	819	(6,270)	519
Income tax benefit (expense)	1,360	(234)	10,048	(2,780)
Comprehensive income	$ 113,969	$ 138,876	$ 319,259	$ 394,277