Inventories - Additional Information (Detail) - USD ($)	12 Months Ended
	Apr. 30, 2016	Apr. 30, 2015
Inventories [Line Items]
LIFO inventory reserve	$ 714,000	$ 1,000,000
Increase or decrease in cost of sales as a result of liquidation of LIFO inventory	336,000	158,000
International Subsidiaries [Member]
Inventories [Line Items]
Inventories measured using FIFO method	$ 2,253,000	$ 1,906,000