Self-Insurance Reserves - Additional Information (Detail) - USD ($)	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015	Apr. 30, 2014
Commitments And Contingencies Disclosure [Abstract]
Reserves for workers' compensation, product liability, municipal liability, and medical/dental costs	$ 8,663,000	$ 10,082,000	$ 9,610,000	$ 9,185,000
Reserves for workers' compensation, product liability, municipal liability, and medical/dental costs, Non-current portion	4,800,000	5,800,000
Reserves for workers' compensation, product liability, municipal liability, and medical/dental costs, included in accrued expenses	3,600,000	4,300,000
Workers' compensation receivable classified as an other assets	590,000	621,000
Accrued reserves for product and municipal litigation liabilities	3,200,000	3,800,000
Accrued reserves for product and municipal litigation liabilities, Non-current portion	2,900,000	3,100,000
Receivables from insurance carriers, included in other assets	$ 1,900,000	$ 1,900,000