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Fair Value of Financial Instruments - Narrative (Detail) (Short-term investments [Member], USD $)
Jan. 27, 2013
Apr. 29, 2012
Short-term investments [Member]
   
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Short-term bond funds $ 5,200,000 $ 5,100,000
Unrealized gains on short-term bond funds $ 26,000 $ 16,000