Key Assumptions Used to Apply Black-Scholes Option Pricing Model (Detail) (Stock options)	6 Months Ended
Jul. 30, 2011 Year	Jul. 31, 2010 Year
Stock options
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Risk-free interest rate	2.80%	3.10%
Expected life of options	6.9	6.8
Expected volatility of underlying stock	81.40%	79.70%
Expected dividend yield	0.00%	0.00%

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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