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Stock-Based Compensation - Weighted Average Assumptions Used to Estimate Fair Values (Detail)	3 Months Ended
	Aug. 31, 2013	Aug. 31, 2012
Common Stock and Stock-based Compensation [Abstract]
Dividend yield	1.30%	1.50%
Expected volatility	27.90%	35.00%
Weighted average expected life (in years)	5 years 3 months 18 days	5 years 3 months 18 days
Risk-free interest rate	1.30%	0.60%

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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