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Inventories - Summary of Inventories (Detail) - USD ($)
$ in Thousands
Jan. 31, 2018
Apr. 30, 2017
Inventory Disclosure [Abstract]    
Finished products $ 3,778 $ 3,179
Work in process 2,133 1,950
Raw materials 11,769 9,806
Total inventories $ 17,680 $ 14,935