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Common Stock Repurchase Program (Detail) - USD ($)
 3 Months Ended 9 Months Ended
Jan. 27, 2019
Oct. 28, 2018
Jul. 29, 2018
Jan. 27, 2019
Jan. 28, 2018
Jun. 15, 2016
Stockholders Equity Note [Line Items]            
Cost of common stock repurchase $ 2,472,000 $ 772,000 $ 72,000      
Common Stock [Member]            
Stockholders Equity Note [Line Items]            
Common stock repurchased 123,543 33,890 2,990      
Cost of common stock repurchase $ 6,000 $ 2,000        
Common Stock Repurchase Program June 15, 2016 [Member] | Common Stock [Member]            
Stockholders Equity Note [Line Items]            
Authorization amount for repurchase of common stock           $ 5,000,000
Common stock repurchased       160,423 0  
Cost of common stock repurchase       $ 3,300,000    
Remaining authorized repurchase amount $ 1,700,000     $ 1,700,000