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Share-Based Compensation (Details 1)	3 Months Ended
Share-Based Compensation (Details 1)	Mar. 31, 2013	Mar. 31, 2012
Stock options granted under the Company's option plans
Expected term (years)	5 years 11 months 6 days	5 years 9 months 6 days
Stock volatility	33.50%	36.50%
Risk free interest rates	1.00%	1.30%
Dividends during expected terms	1.60%	1.60%

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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