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Inventories - Summary of Inventories (Detail) - USD ($)
$ in Thousands
Jan. 31, 2020
Apr. 30, 2019
Inventory Disclosure [Abstract]    
Finished products $ 3,135 $ 4,139
Work in process 1,796 2,179
Raw materials 10,315 10,888
Total inventories $ 15,246 $ 17,206