Stock Compensation Plans (Details) (USD $)	12 Months Ended
Dec. 31, 2011 years	Dec. 31, 2010 years	Dec. 31, 2009 years
Summary of fair value of awards granted
Risk-free interest rate	2.20%	2.70%	1.70%
Expected life of option in years	5.51	5.61	4
Expected dividend yield of stock	2.50%	3.20%	4.80%
Expected volatility of stock price	49.00%	50.80%	70.50%
Weighted-average per share fair value of options granted	$ 11.42	$ 8.62	$ 5.97

The period of time an equity-based award is expected to be outstanding. An equity-based award's expected term is generally determined based on, among other factors, the instrument's contractual term and the effects of employees' expected exercise and post-vesting employment termination behavior.

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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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