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Fair Value of Financial Instruments - Narrative (Detail) - USD ($)
$ in Thousands
6 Months Ended
Oct. 28, 2018
Apr. 29, 2018
Oct. 29, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Short-term investments - Available for Sale   $ 2,451 [1] $ 2,478
Long-term investments (Rabbi Trust) $ 7,851 7,326 [1] 6,921
U.S. Corporate Bonds [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Held to maturity investments 26,700 30,800 30,900
Held to maturity investments, fair value $ 26,600 30,600 30,800
U.S. Corporate Bonds [Member] | Minimum [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Long-term investments, maturity period 2 years    
U.S. Corporate Bonds [Member] | Maximum [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Long-term investments, maturity period 2 years 6 months    
Short-term Investments [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Accumulated unrealized gain (loss) on investments   (91) (36)
Long-term investments (Rabbi Trust) [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Accumulated unrealized gain (loss) on investments $ 62 $ 61 $ 96
[1] Derived from audited financial statements.