Option Transactions (Detail) (USD $)	12 Months Ended
	May 31, 2012	May 31, 2011	May 31, 2010
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Beginning Balance	1,972,441	1,764,516	1,594,757
Shares Under Option, Granted	389,850	358,450	320,450
Shares Under Option, Exercised	(105,269)	(103,280)	(122,884)
Shares Under Option, Canceled	(111,452)	(47,245)	(27,807)
Ending Balance	2,145,570	1,972,441	1,764,516
Beginning Balance	$ 39.58	$ 38.54	$ 38.03
Weighted-Average Option Price, Granted	$ 29.75	$ 40.22	$ 36.15
Weighted-Average Option Price, Exercised	$ 21.44	$ 22.51	$ 25.50
Weighted-Average Option Price, Canceled	$ 42.31	$ 43.13	$ 39.20
Ending Balance	$ 38.54	$ 39.58	$ 38.54