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Assumptions Used to Estimate Fair Values of Option Granted (Detail)	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, minimum	1.18%	2.29%
Risk-free interest rate, maximum	1.49%	2.81%
Expected life of options (in years)	7 years 6 months	7 years 6 months
Expected stock price volatility	108.00%	111.00%

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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