XML 49 R38.htm IDEA: XBRL DOCUMENT v3.7.0.1
Inventories - Additional Information (Detail) - USD ($)
12 Months Ended
Apr. 30, 2017
Apr. 30, 2016
Inventories [Line Items]    
LIFO inventory reserve $ 748,000 $ 714,000
Increase or decrease in cost of product sales as a result of liquidation of LIFO inventory 14,000 336,000
International Subsidiaries [Member]    
Inventories [Line Items]    
Inventories measured using FIFO method $ 2,205,000 $ 2,253,000