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Stock Option and Purchase Plans (Details 5)	12 Months Ended
Stock Option and Purchase Plans (Details 5)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Fair value for the options granted under the Employee Stock Purchase Plan
Dividend Yield	0.00%	0.00%	0.00%
Employee Stock [Member]
Fair value for the options granted under the Employee Stock Purchase Plan
Risk-free Interest Rate	0.17%	0.10%	0.25%
Dividend Yield	0.00%	0.00%	0.00%
Volatility Factor	0.37%	0.52%	0.40%
Expected Life in Years	1 year	1 year	1 year

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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