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SEGMENT INFORMATION - Narrative (Details) - Sales Revenue, Net - Geographic Concentration Risk
12 Months Ended
May 31, 2016
May 31, 2015
May 31, 2014
United States      
Segment Reporting Information [Line Items]      
Percentage of total consolidated revenues from external customers 61.00% 60.00% 58.00%
United Kingdom      
Segment Reporting Information [Line Items]      
Percentage of total consolidated revenues from external customers 10.00% 13.00% 13.00%
Canada      
Segment Reporting Information [Line Items]      
Percentage of total consolidated revenues from external customers 10.00% 11.00% 13.00%