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Inventories - Summary of Inventories (Detail) - USD ($)
$ in Thousands
Oct. 31, 2019
Apr. 30, 2019
Inventory Disclosure [Abstract]    
Finished products $ 3,068 $ 4,139
Work in process 1,878 2,179
Raw materials 9,832 10,888
Total inventories $ 14,778 $ 17,206