Benefit Plans (Significant Assumptions Used to Estimate Fair Value of Stock Options and SARS) (Details)	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Weighted average expected life of the securities granted (in years)	5.61	5.61	4.84
Estimate of the underlying common stock's volatility	39.88%	39.58%	39.95%
Expected dividend yield	1.50%
Risk free interest rate	2.20%	2.60%	2.00%

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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