Investment (Income), Net (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Nov. 30, 2015	Nov. 30, 2014	Nov. 30, 2015	Nov. 30, 2014
Other Income And Expenses [Abstract]
Interest (income)	$ (1,218)	$ (1,601)	$ (2,582)	$ (3,005)
(Gain) on sale of marketable securities	(2,042)	(3,204)	(4,418)	(5,320)
Other-than-temporary impairment on securities	2,472		2,472
Dividend (income)	(312)	(253)	(640)	(536)
Investment (income), net	$ (1,100)	$ (5,058)	$ (5,168)	$ (8,861)