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Activity in Allowance for Doubtful Accounts (Detail) (USD $)
12 Months Ended
May 31, 2013
May 31, 2012
May 31, 2011
Financing Receivable, Allowance for Credit Losses [Line Items]      
Beginning Balance $ 800,000 $ 800,000 $ 600,000
Provision 193,033 90,821 446,346
Recoveries 24,029 12,211 88,175
Write-offs, net (117,062) (103,032) (334,521)
Ending Balance $ 900,000 $ 800,000 $ 800,000