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Share-Based Payment Arrangements - Stock Options Valuation Assumption (Detail)	9 Months Ended
	Sep. 30, 2012
Share Based Payment Award Stock Options Valuation Assumptions [Line Items]
Expected volatility	38.64%
Dividend yield	3.23%
Expected term	6 years 6 months 29 days
Risk-free interest rate	1.78%

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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