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Stock Compensation Plans (Details) (USD $)	12 Months Ended
Stock Compensation Plans (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary of fair value of awards granted
Risk-free interest rate (in hundredths)	1.00%	2.20%	2.70%
Expected life of option in years	5 years 4 months 21 days	5 years 6 months 4 days	5 years 7 months 10 days
Expected dividend yield of stock (in hundredths)	2.30%	2.50%	3.20%
Expected volatility of stock price (in hundredths)	56.40%	49.00%	50.80%
Weighted-average per share fair value of options granted (in dollars per share)	$ 12.36	$ 11.42	$ 8.62

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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