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Weighted Average Assumptions for Option Grants (Detail)	9 Months Ended
Weighted Average Assumptions for Option Grants (Detail)	Sep. 29, 2012	Sep. 24, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	34.00%	35.00%
Expected dividend yield	0.42%	0.45%
Risk-free interest rate	0.90%	1.75%
Expected lives (in years)	4 years	4 years

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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