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Inventories - Summary of Inventories (Detail) - USD ($)
$ in Thousands
Jul. 31, 2018
Apr. 30, 2018
Inventory Disclosure [Abstract]    
Finished goods $ 3,466 $ 4,751
Work-in-process 1,248 2,278
Materials and components 10,292 10,633
Total inventories $ 15,006 $ 17,662