Investment (Income), Net (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Feb. 29, 2016	Feb. 28, 2015	Feb. 29, 2016	Feb. 28, 2015
Other Income And Expenses [Abstract]
Interest (income)	$ (2,019)	$ (3,687)	$ (4,602)	$ (6,692)
(Gain) on sale of marketable securities	(1,020)	(3,356)	(5,438)	(8,677)
Other-than-temporary impairment on securities	839		3,312
Dividend (income)	(709)	(650)	(1,349)	(1,185)
Investment (income), net	$ (2,909)	$ (7,693)	$ (8,077)	$ (16,554)