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Stock Options and Share-Based Compensations - Additional Information (Detail) - USD ($)
12 Months Ended
Apr. 30, 2015
Apr. 30, 2014
Apr. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period 4 years    
Stock based compensation expense $ 196,000 $ 238,000 $ 239,000
Deferred income tax benefit 75,000 $ 93,000 $ 93,000
Compensation expense not yet recorded 414,000    
Deferred income tax on remaining compensation expense $ 158,000    
2010 Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
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 will be 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    
Shares available for future grants 25,000    
2008 Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of shares authorized under stock option plan 300,000    
Shares available for future grants 29,950    
2008 Plan [Member] | Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Terms of award 10 years