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Self-Insurance Reserves - Additional Information (Detail) - USD ($)
Apr. 30, 2018
Apr. 30, 2017
Apr. 30, 2016
Apr. 30, 2015
Commitments And Contingencies Disclosure [Abstract]        
Reserves for workers' compensation, product liability, municipal liability, and medical/dental costs $ 9,173,000 $ 8,663,000 $ 10,082,000 $ 9,610,000
Reserves for workers' compensation, product liability, municipal liability, and medical/dental costs, Non-current portion 4,800,000 4,800,000    
Reserves for workers' compensation, product liability, municipal liability, and medical/dental costs, included in accrued expenses 3,900,000 3,600,000    
Workers' compensation receivable classified as an other assets 590,000 590,000    
Accrued reserves for product and municipal litigation liabilities 3,400,000 3,200,000    
Accrued reserves for product and municipal litigation liabilities, Non-current portion 2,900,000 2,900,000    
Receivables from insurance carriers, included in other assets $ 1,900,000 $ 1,900,000