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Commitments and Contingencies - Additional Information (Detail)
 3 Months Ended
Jul. 31, 2015
USD ($)
Case
Claim
Apr. 30, 2015
USD ($)
May. 05, 2014
USD ($)
Schedule Of Commitments And Contingencies [Line Items]      
Number of Product liability cases | Case 7    
Number of Other product liability claims | Claim 8    
Insurance recovery as a result of an insurance settlement agreement $ 1,800,000    
Environmental reserve in non-current liabilities 675,000 $ 675,000  
Amount placed in escrow     $ 3,000,000
Escrow deposit, remaining amount     $ 1,400,000
Minimum      
Schedule Of Commitments And Contingencies [Line Items]      
Compensatory damages sought 75,000    
Maximum      
Schedule Of Commitments And Contingencies [Line Items]      
Compensatory damages sought $ 1,500,000