XML 55 R79.htm IDEA: XBRL DOCUMENT

Stock-Based Compensation (Details 3) (Stock options)	12 Months Ended
Stock-Based Compensation (Details 3) (Stock options)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Weighted average assumptions used for determining fair value of options
Expected dividend yield (as a percent)	0.00%	0.00%	0.00%
Minimum
Weighted average assumptions used for determining fair value of options
Risk-free interest rate (as a percent)	0.70%	1.30%	1.70%
Expected term	5 years	5 years	5 years
Expected volatility (as a percent)	66.00%	71.00%	73.00%
Maximum
Weighted average assumptions used for determining fair value of options
Risk-free interest rate (as a percent)	1.10%	2.50%	2.80%
Expected term	5 years 10 months 24 days	5 years 10 months 24 days	5 years 10 months 24 days
Expected volatility (as a percent)	72.00%	73.00%	77.00%

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.

+ References+ Details