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Stock Options and Share-Based Compensation - Additional Information (Detail) - USD ($)
12 Months Ended
Aug. 30, 2017
Apr. 26, 2015
Apr. 30, 2018
Apr. 30, 2017
Apr. 30, 2016
Aug. 25, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Awards granted       45,200 40,200  
Vesting period     4 years      
Stock based compensation expense     $ 172,000 $ 199,000 $ 192,000  
Deferred income tax benefit     42,000 $ 74,000 $ 72,000  
Compensation expense not yet recorded     209,000      
Deferred income tax on remaining compensation expense     $ 51,000      
2010 and 2008 Plan [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Shares available for future grants 280,100   263,942      
2010 Plan [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Shares available for future grants     0      
Awards granted 0          
Number of shares authorized under stock option plan     100,000      
Number of shares each director can purchase     10,000      
Terms of award     5 years      
Stock options plan, description     Options are exercisable in four equal installments, one-fourth becoming exercisable on the next August 1 following the date of grant, and one-fourth becoming exercisable on August 1 of each of the next three years.      
2008 Plan [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Shares available for future grants     0      
Awards granted 0     45,200 40,200  
Increase in number of shares available under stock option plan   300,000        
Number of shares authorized under stock option plan           300,000
2008 Plan [Member] | Maximum [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Terms of award     10 years      
2017 Plan [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Increase in number of shares available under stock option plan 0          
2017 Plan [Member] | Restricted Stock Units (RSUs) [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock-based compensation expense     $ 141,000      
Vesting period     3 years      
Remaining estimated compensation expense     $ 394,000