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Fair Value of Financial Instruments - Narrative (Detail) - USD ($)
3 Months Ended
Oct. 30, 2016
Jan. 28, 2018
Apr. 30, 2017
Jan. 29, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]        
Short-term investments - Available for Sale   $ 2,472,000 $ 2,443,000 [1] $ 2,410,000
Long-term investments (Rabbi Trust)   7,176,000 5,466,000 [1] 5,488,000
U.S. Corporate Bonds [Member]        
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]        
Held to maturity investments $ 31,000,000 30,800,000 30,900,000 30,800,000
Held to maturity investments, fair value   30,700,000 30,800,000 30,700,000
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   (57,000) (47,000) (68,000)
Long-term investments (Rabbi Trust) [Member]        
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]        
Accumulated unrealized gain (loss) on investments   $ 113,000 $ 43,000 $ 11,000
[1] Derived from audited financial statements.