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Stock-Based Compensation - Fair Value Assumptions (Details) (Stock Options)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Volatility	45.00%	44.00%	43.00%
Risk free interest rate	1.07%	2.13%	2.49%
Expected life (months)	71 months	70 months	66 months
Dividend yield	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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