SARs Fair Value Assumptions (Details) (Stock Appreciation Rights (SARs), USD $)	3 Months Ended
Mar. 31, 2013 Rate	Mar. 31, 2012 Rate
Stock Appreciation Rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award
Expected term of award	6 years	6 years
Risk-free interest rate	1.00%	1.10%
Expected Volatility	65.50%	64.30%
Weighted-average grant date fair value per share	$ 21.96	$ 17.61

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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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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