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Stock Options and Share-Based Compensation - Summary of Options Outstanding, Exercisable, and Weighted Average Exercise Prices within Exercise Price Range (Detail) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Apr. 30, 2021
Apr. 30, 2020
Apr. 30, 2019
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]      
Options outstanding (in shares) 84,300 88,000 104,350
Weighted average exercise price (in dollar per shares) $ 18.56 $ 18.45 $ 18.28
Exercise Price Range Range One      
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]      
Exercise price range lower limit (in dollar per shares) 8.59    
Exercise price range upper limit (in dollar per shares) $ 11.78    
Options outstanding (in shares) 5,150    
Weighted average exercise price (in dollar per shares) $ 10.85    
Weighted average remaining contractual life (in years) 1 year 14 days    
Aggregate intrinsic value $ 5,918    
Options exercisable (in shares) 5,150    
Weighted average exercise price (in dollar per shares) $ 10.85    
Aggregate intrinsic value $ 5,918    
Exercise Price Range Range Two      
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]      
Exercise price range lower limit (in dollar per shares) $ 15.85    
Exercise price range upper limit (in dollar per shares) $ 23.62    
Options outstanding (in shares) 79,150    
Weighted average exercise price (in dollar per shares) $ 19.06    
Weighted average remaining contractual life (in years) 4 years 2 months 1 day    
Aggregate intrinsic value $ 0    
Options exercisable (in shares) 79,150    
Weighted average exercise price (in dollar per shares) $ 19.06    
Aggregate intrinsic value $ 0