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Summary of Assumptions to Value Employee Options (Detail) (Employee Stock Option [Member])	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life	5 years	5 years
Risk-free interest rate	0.71%	1.97%
Expected volatility	102.00%	115.00%
Expected dividend yield	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.

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