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Common Stock Repurchase Program (Detail) - USD ($)
 12 Months Ended
Apr. 30, 2017
May 01, 2016
May 03, 2015
Jun. 15, 2016
Stockholders Equity Note [Line Items]        
Cost of common stock repurchased   $ 2,397,000 $ 745,000  
Common Stock [Member]        
Stockholders Equity Note [Line Items]        
Common stock repurchased   100,776 43,014  
Cost of common stock repurchased   $ 5,000 $ 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 0 100,776 43,014  
Cost of common stock repurchased   $ 2,400,000 $ 745,000  
Remaining authorized repurchase amount $ 5,000,000