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Inventories - Summary of Inventories (Detail) - USD ($)
$ in Thousands
Jan. 31, 2016
Apr. 30, 2015
Inventory Disclosure [Abstract]    
Finished products $ 4,117 $ 2,936
Work in process 1,633 1,422
Raw materials 10,404 8,387
Total inventories $ 16,154 $ 12,745