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Stock-Based Compensation (Details) (USD $)	6 Months Ended
Stock-Based Compensation (Details) (USD $)	Jun. 30, 2012	Jun. 30, 2011
Summary of fair value of each SAR is estimated on the date of grant using Black-Scholes option-pricing formula
Weighted-average fair value of grants	$ 14.01	$ 14.57
Dividend yield	0.00%	0.00%
Average risk-free interest rate	0.80%	2.00%
Expected term (years)	5 years	5 years
Expected volatility	66.00%	65.00%

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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