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Share-based Compensation-Fair Value Assumptions (Details) (Employee Stock Option [Member])	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield (percent)	1.95%	2.00%
Expected life of option	4 years 8 months 12 days	3 years 8 months 12 days
Risk-free interest rate (percent)	0.78%	0.46%
Expected stock price volatility	35.59%	37.40%

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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