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Share-base Compensation - Fair Value Assumptions Used (Details) (Stock Options [Member])	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-Free Interest Rate	1.16%	1.37%	2.39%
Expected Term	6 years 7 months 6 days	6 years 6 months	5 years 9 months 11 days
Expected Volatility	40.00%	40.70%	55.00%
Expected 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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