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Fair Value of Options Granted (Detail)	3 Months Ended
Fair Value of Options Granted (Detail)	Mar. 30, 2013	Mar. 31, 2012
Fair Value, Option, Quantitative Disclosures [Line Items]
Risk-free interest rate	0.55%	0.66%
Expected dividend yield	0.00%	0.00%
Expected option life	4 years	4 years
Expected volatility	48.40%	50.70%
Weighted-average expected volatility	48.40%	50.70%

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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