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Shareholders' Equity (Details)	3 Months Ended
Shareholders' Equity (Details)	Mar. 31, 2013	Mar. 31, 2012
Fair values of stock option grants estimated with weighted average assumptions
Dividend yield	0.00%	0.00%
Expected life	3 years 8 months 12 days	3 years 10 months 24 days
Expected volatility	68.00%	73.00%
Risk-free interest rate	0.60%	0.70%

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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