Investment (Income), Net (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Nov. 30, 2016	Nov. 30, 2015	Nov. 30, 2016	Nov. 30, 2015
Other Income And Expenses [Abstract]
Interest (income)	$ (1,093)	$ (1,218)	$ (2,233)	$ (2,582)
(Gain) on sale of marketable securities	(1,114)	(2,042)	(3,698)	(4,418)
Other-than-temporary impairment on securities	217	2,472	403	2,472
Dividend (income)	(426)	(312)	(726)	(640)
Investment (income), net	$ (2,416)	$ (1,100)	$ (6,254)	$ (5,168)