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Stock-Based Compensation - Assumptions and Weighted Average Fair Values (Detail) (USD $)	12 Months Ended
	Dec. 31, 2010
Stock Based Compensation [Line Items]
Weighted average fair value of grants	$ 6.78
Valuation assumptions:
Expected dividend yield	0.00%
Expected volatility	68.44%
Expected life (in years)	4 years 5 months 9 days
Risk-free interest rate	1.71%

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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