XML 79 R56.htm IDEA: XBRL DOCUMENT

Schedule of Estimated Fair Value of Stock Options Assumptions (Detail) (Stock Purchase Rights)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock Purchase Rights
Share-based Compensation Arrangement by Share-based Payment Award
Expected life (years)	6 months	6 months	6 months
Interest rate	0.10%	0.10%	0.20%
Volatility-historical	42.70%	41.00%	48.00%
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