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Estimated Fair Value of Stock Option Grant (Detail)	3 Months Ended		6 Months Ended
Estimated Fair Value of Stock Option Grant (Detail)	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rates			0.70%	1.80%
Expected lives (in years)			4 years 6 months	4 years 256 days
Volatility			51.00%	48.00%
Dividend yield

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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