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Weighted Average Assumptions (Detail)	12 Months Ended
Weighted Average Assumptions (Detail)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2008
Share Based Compensation Plans [Line Items]
Risk-free interest rate	0.78%	2.30%	3.10%
Dividend yield	0.00%	0.00%	0.00%
Expected volatility	185.00%
Expected term in months	61 months	81 months	76 months

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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