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Valuation Accounts (Detail) (Allowance for Doubtful Accounts [Member], USD $)
In Thousands, unless otherwise specified
12 Months Ended
Apr. 30, 2013
Apr. 30, 2012
Apr. 30, 2011
Allowance for Doubtful Accounts [Member]
     
Valuation and Qualifying Accounts Disclosure [Line Items]      
Allowance of doubtful accounts, beginning balance $ 740 $ 920 $ 1,602
Additions -Charged to expense 2,072 730 363
Deductions -Bad debts written off, net of recoveries (1,239) (911) (1,045)
Allowance of doubtful accounts, ending balance $ 1,573 $ 740 $ 920