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Activity in Allowance for Doubtful Accounts (Detail) - USD ($)
$ in Thousands
12 Months Ended
May. 31, 2015
May. 31, 2014
May. 31, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]      
Beginning Balance $ 1,200 $ 900 $ 800
Provision 337 367 193
Recoveries 92 8 24
Write-offs (329) (75) (117)
Ending Balance $ 1,300 $ 1,200 $ 900