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Inventories - Summary of Inventories (Detail) - USD ($)
$ in Thousands
Jan. 31, 2019
Apr. 30, 2018
Inventory [Line Items]    
Finished products   $ 4,987
Work in process   2,393
Raw materials   11,169
Total inventories $ 16,672 18,549
As Adjusted Under FIFO    
Inventory [Line Items]    
Finished products 3,591  
Work in process 1,804  
Raw materials 11,277  
Total inventories $ 16,672 $ 17,662