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Inventories - Summary of Inventories (Detail) - USD ($)
$ in Thousands
Oct. 31, 2018
Apr. 30, 2018
Inventory [Line Items]    
Total inventories $ 17,097 $ 17,662
Fifo [Member]    
Inventory [Line Items]    
Finished products 3,807 4,987
Work in process 1,375 2,393
Raw materials 11,915 11,169
Total inventories $ 17,097 $ 18,549