Share Based Compensation (Details) (USD $)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Weighted Average Estimated Fair Value
Weighted average estimated fair value	$ 18.48	$ 13.88	$ 11.13
Quarterly dividend rate	$ 0.29	$ 0.29	$ 0.28
Expected term of SAR, in years	4 years 8 months 15 days	4 years 3 months 19 days	4 years 3 months 19 days
Risk-free interest rate	1.00%	1.60%	2.00%
Dividend yield	2.70%	3.40%	4.30%
Expected stock price volatility	43.30%	41.90%	41.80%
Present value of dividends	$ 5.37	$ 4.76	$ 4.55

The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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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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