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Stock Based Compensation Binomial Option Pricing Model (Details)	9 Months Ended
	Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, minimum	0.20%
Risk-free interest rate, maximum	2.90%
Weighted-average volatility	21.10%
Dividend yield	2.72%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected years until exercise	6 years 7 months 6 days
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected years until exercise	7 years 7 months 6 days

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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