Weighted-Average Grant Date Fair Value of Options Granted and Weighted-Average Assumptions Used for Grants (Detail) (USD $)	12 Months Ended
	May 31, 2012	May 31, 2011	May 31, 2010
Stock-Based Compensation Plans
Weighted average grant date fair value	$ 13.80	$ 18.52	$ 16.83
Expected volatility	0.450	0.462	0.469
Expected option term in years	6 years 8 months 12 days	6 years 8 months 12 days	6 years 6 months
Risk-free interest rate	1.31%	2.68%	3.20%
Expected dividend yield	0.02%	0.74%	0.83%