XML 29 R61.htm IDEA: XBRL DOCUMENT

Employee Benefit Plans, Assumptions and Resulting Estimates of Fair Value (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Stock Options [Member]
Estimates of Fair Value
Expected Volatility Rate		46.00%
Risk Free Interest Rate		0.80%
Expected Term		4 years 2 months 12 days
Dividend yield		0.00%
Weighted-average fair value per share		$ 8.51
Employee Stock Purchase Plan [Member]
Estimates of Fair Value
Expected Volatility Rate	36.00%	51.00%
Risk Free Interest Rate	0.10%	0.10%
Expected Term	6 months	6 months
Dividend yield	0.00%	0.00%
Weighted-average fair value per share	$ 5.63	$ 6.38

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