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Activity in Allowance for Doubtful Accounts (Detail) - USD ($)
$ in Thousands
 12 Months Ended
May 31, 2017
May 31, 2016
May 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]      
Beginning Balance $ 1,500 $ 1,300 $ 1,200
Provision 645 305 337
Recoveries 25 90 92
Write-offs (170) (195) (329)
Ending Balance $ 2,000 $ 1,500 $ 1,300