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Commitments and Contingencies - Additional Information (Detail)
 12 Months Ended
Apr. 30, 2017
USD ($)
Case
Claim
Apr. 30, 2016
USD ($)
Apr. 30, 2015
USD ($)
Schedule Of Commitments And Contingencies [Line Items]      
Number of Product liability cases | Case 3    
Number of Other product liability claims | Claim 12    
Defense and administrative costs $ 254,000 $ 264,000 $ 252,000
Settlement fees related to product liability cases 209,000 55,000 177,000
Gain from changes in product liability provisions 364,000    
Expense related to changes in product liability and municipal litigation liability   299,000 183,000
Environmental reserve in non-current liabilities 730,000 694,000  
Rent expense 4,400,000 4,100,000 $ 3,300,000
General and Administrative Expense      
Schedule Of Commitments And Contingencies [Line Items]      
Insurance recovery as a result of an insurance settlement agreement   $ 1,800,000  
Minimum      
Schedule Of Commitments And Contingencies [Line Items]      
Compensatory damages sought 75,000    
Maximum      
Schedule Of Commitments And Contingencies [Line Items]      
Compensatory damages sought $ 350,000