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Fair Value of Financial Instruments - Narrative (Detail) - USD ($)
$ in Thousands
9 Months Ended
Jan. 27, 2019
Apr. 29, 2018
Jan. 28, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Short-term investments - Available for Sale $ 0 $ 2,451 [1] $ 2,472
Long-term investments (Rabbi Trust) 6,834 7,326 [1] 7,176
U.S. Corporate Bonds [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Held to maturity investments 13,500 30,800 30,800
Held to maturity investments, fair value $ 13,500 30,600 30,700
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) (57)
Long-term investments (Rabbi Trust) [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Accumulated unrealized gain (loss) on investments $ 9 $ 61 $ 113
[1] Derived from audited financial statements.