XML 109 R74.htm IDEA: XBRL DOCUMENT

Weighted Average Assumptions Used to Value Stock-Based Awards (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield	0.00%
Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	5 years 6 months 15 days	5 years 3 months 18 days	5 years 4 months 24 days
Estimated volatility	67.00%	68.00%	82.00%
Risk-free interest rate	1.03%	1.23%	1.40%
Expected dividend yield	0.00%	0.00%	0.00%
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 months	6 months	6 months
Estimated volatility	101.00%	48.00%	61.00%
Risk-free interest rate	0.14%	0.08%	0.89%
Expected dividend yield	0.00%	0.00%	0.00%

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