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Stock-based Compensation (Summary of the Assumptions Used in the Monte Carlo Simulation to Determine the Grant-Date Fair Value) (Details)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Share-based Compensation [Abstract]
Risk-free rate	1.40%	1.50%	1.30%
Expected volatility	48.00%	49.00%	46.00%
Expected dividend rate	0.00%	0.00%	0.00%

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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