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Activity in Allowance for Doubtful Accounts (Detail) - USD ($)
$ in Thousands
12 Months Ended
May 31, 2018
May 31, 2017
May 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]      
Beginning Balance $ 2,000 $ 1,500 $ 1,300
Provision 152 645 305
Recoveries 40 25 90
Write-offs (642) (170) (195)
Ending Balance $ 1,550 $ 2,000 $ 1,500