XML 105 R82.htm IDEA: XBRL DOCUMENT

Share-Based Compensation - Estimate Fair Value of Share-Based Awards with Weighted-Average Assumptions (Detail) (Options Granted During the Period [Member], USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Options Granted During the Period [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividends	2.60%	2.60%
Expected volatility	34.80%	41.00%
Risk-free interest rate	1.70%	0.90%
Expected term (in years)	8 years 7 months 6 days	5 years
Weighted-average grant-date fair value	$ 15.37	$ 14.74

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.

+ References+ Details