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Fair Value of Financial Instruments - Narrative (Detail) - USD ($)
3 Months Ended
Oct. 30, 2016
Jul. 30, 2017
Apr. 30, 2017
Jul. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]        
Short-term investments   $ 2,469,000 $ 2,443,000 [1] $ 2,434,000
Held to maturity investments   30,907,000 30,945,000 [1]  
Long-term investments (Rabbi Trust)   6,714,000 5,466,000 [1] 4,611,000
U.S. Corporate Bonds [Member]        
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]        
Held to maturity investments $ 31,000,000 30,907,000 30,945,000  
Held to maturity investments, fair value   30,846,000 30,831,000  
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 long-term investments   (33,000) (47,000) (33,000)
Long-term investments (Rabbi Trust) [Member]        
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]        
Accumulated unrealized gain (loss) on long-term investments   $ 73,000 $ 43,000 $ (15,000)
[1] Derived from audited financial statements.