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Inventories - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
Oct. 31, 2012
Apr. 30, 2012
Inventory Disclosure [Line Items]    
Inventories, net $ 35,347 $ 34,299
UNITED STATES
   
Inventory Disclosure [Line Items]    
Inventories, net 25,000 25,500
BELGIUM
   
Inventory Disclosure [Line Items]    
Inventories, net 9,600 8,200
CHINA
   
Inventory Disclosure [Line Items]    
Inventories, net $ 700 $ 600