SCHEDULE II - Valuation and Qualifying Accounts (Detail) - Allowance for Doubtful Accounts - USD ($)		12 Months Ended
		May. 31, 2015	May. 31, 2014	May. 31, 2013
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period		$ 3,043,000	$ 3,408,000	$ 3,329,000
Charged to Costs and Expenses		259,000	32,000	783,000
Charged to Other Accounts - Describe	[1]			26,000
Deductions - Describe	[2]	217,000	397,000	730,000
Balance at End of Period		$ 3,085,000	$ 3,043,000	$ 3,408,000

[1] Miscellaneous amounts.

[2] Uncollectable accounts charged to the allowance.