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Stock-Based Payment (Detail) - Valuation Assumption (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Expected volatility	84.00%	80.20%
Risk-free interest rate	1.10%	1.90%
Dividend yield	0.00%	0.00%
Expected life in years	5.9	5.2
Weighted average grant date fair value (in Dollars per share)	$ 2.04	$ 3.49

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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