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Equity Incentive Plans (Details) Black-Scholes Assumptions	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation
Average expected term	5 years 7 months 6 days	5 years 9 months 18 days	5 years 8 months 12 days
Risk free interest rate, minimum	0.80%	1.14%	1.39%
Risk free interest rate, maximum	1.15%	2.55%	2.80%
Expected dividend rate	0.00%	0.00%	0.00%
Minimum [Member]
Share-based Compensation
Expected volatility rate	64.00%	64.00%	65.80%
Maximum [Member]
Share-based Compensation
Expected volatility rate	69.20%	65.10%	70.80%

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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