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Inventories (Details) (USD $)
In Thousands, unless otherwise specified
Oct. 31, 2012
Apr. 30, 2012
Summary of inventories    
Finished goods $ 16,713 $ 14,017
Finished parts 33,975 28,936
Work in process 9,940 7,889
Raw materials 4,707 4,454
Total inventories $ 65,335 $ 55,296