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Stock-based Compensation (Details 2)	6 Months Ended		12 Months Ended
Stock-based Compensation (Details 2)	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011	Dec. 31, 2010
Details of fair value option award
Expected life (years)	6 years	5 years 3 months 18 days	5 years 4 months 24 days	5 years 1 month 6 days
Interest rate	2.30%	2.30%	2.10%	2.00%
Dividend yield	0.00%	0.00%	0.00%	0.00%
Volatility	60.00%	62.00%	62.00%	64.00%

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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