SCHEDULE II - Valuation and Qualifying Accounts (Detail) - Allowance for Doubtful Accounts - USD ($)		12 Months Ended
		May 31, 2017	May 31, 2016	May 31, 2015
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period		$ 4,579,000	$ 3,085,000	$ 3,043,000
Charged to Costs and Expenses		269,000	1,556,000	259,000
Charged to Other Accounts - Describe	[1]		394,000
Deductions - Describe	[2]	1,404,000	456,000	217,000
Balance at End of Period		$ 3,444,000	$ 4,579,000	$ 3,085,000

[1] Miscellaneous amounts.

[2] Uncollectable accounts charged to the allowance.