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Share-based Compensation - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended
Jan. 31, 2018
Jan. 31, 2018
Jan. 31, 2017
Aug. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock-based compensation expense   $ 276,000 $ 150,000  
2010 and 2008 Plan [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares available for issuance       280,100
2010 Plan [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Awards granted   0    
2008 Plan [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Awards granted   0    
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 $ 60,000 $ 100,000    
Vesting period   3 years    
Remaining estimated compensation expense $ 510,000 $ 510,000