Weighted-Average Assumptions Used to Estimate Fair Value of Stock Options Granted (Detail) (Stock Options, USD $)	3 Months Ended
Oct. 29, 2011 Year	Oct. 30, 2010 Year
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (years)	4.0	4.0
Expected volatility	41.70%	41.30%
Risk-free interest rate	0.90%	2.10%
Expected dividend yield	0.00%	0.00%
Weighted-average grant date fair value	$ 9.41	$ 8.65

The period of time an equity-based award is expected to be outstanding. An equity-based award's expected term is generally determined based on, among other factors, the instrument's contractual term and the effects of employees' expected exercise and post-vesting employment termination behavior.

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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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