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Inventories - Additional Information (Detail) - USD ($)
Jan. 31, 2018
Apr. 30, 2017
Inventories [Line Items]    
LIFO inventory amount $ 15,833,000 $ 12,730,000
International Subsidiaries [Member]    
Inventories [Line Items]    
Inventories measured using FIFO method $ 1,847,000 $ 2,205,000