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Investment (Income), Net (Detail) - USD ($)
$ in Thousands
12 Months Ended
May. 31, 2015
May. 31, 2014
May. 31, 2013
Net Investment Income [Line Items]      
Interest (income) $ (8,304) $ (6,327) $ (6,814)
(Gain) on sale of marketable securities (8,692) (7,353) (11,664)
Other-than-temporary impairment on securities 22 161 14,279
Dividend (income) (1,603) (2,196) (1,979)
Investment (income), net $ (18,577) $ (15,715) $ (6,178)