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Investment (Income), Net (Detail) - USD ($)
$ in Thousands
3 Months Ended
Aug. 31, 2015
Aug. 31, 2014
Net Investment Income [Line Items]    
Interest (income) $ (1,364) $ (1,404)
(Gain) on sale of marketable securities (2,376) (2,116)
Dividend (income) (328) (283)
Investment (income), net $ (4,068) $ (3,803)