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Fair Value of Financial Instruments - Narrative (Detail) - USD ($)
3 Months Ended
Jul. 29, 2018
Apr. 29, 2018
Jul. 30, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Short-term investments - Available for Sale   $ 2,451,000 [1] $ 2,469,000
Long-term investments (Rabbi Trust) $ 7,671,000 7,326,000 [1] 6,714,000
U.S. Corporate Bonds [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Held to maturity investments 30,800,000 30,800,000 30,900,000
Held to maturity investments, fair value $ 30,600,000 30,600,000 30,800,000
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   (91,000) (33,000)
Long-term investments (Rabbi Trust) [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Accumulated unrealized gain (loss) on investments $ 104,000 $ 61,000 $ 73,000
[1] Derived from audited financial statements.