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Inventories - Summary of Inventories (Detail) - USD ($)
$ in Thousands
Jul. 31, 2019
Apr. 30, 2019
Inventory Disclosure [Abstract]    
Finished products $ 3,657 $ 4,139
Work in process 2,185 2,179
Raw materials 10,509 10,888
Total inventories $ 16,351 $ 17,206