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Stock-Based Compensation - Assumptions (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	0.82%	2.11%	1.38%
Expected term	4 years 9 months	4 years 9 months	4 years 9 months
Dividend yield	0.00%	0.00%	0.00%
Expected volatility	93.57%	92.72%	92.45%

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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