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Stockholders Equity - Valuation Assumptions (Detail)	3 Months Ended		9 Months Ended
Stockholders Equity - Valuation Assumptions (Detail)	Jan. 25, 2013	Jan. 27, 2012	Jan. 25, 2013	Jan. 27, 2012
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term in years	4 years 6 months	4 years 9 months 18 days	4 years 9 months 18 days	4 years 9 months 18 days
Risk-free interest rate	0.59%	0.84%	0.63%	1.54%
Volatility	43.00%	43.00%	42.00%	36.00%
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term in years	1 year 2 months 12 days	1 year 2 months 12 days	1 year 2 months 12 days	1 year 2 months 12 days
Risk-free interest rate	0.20%	0.18%	0.19%	0.19%
Volatility	41.00%	45.00%	40.00%	44.00%

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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