Investment (Income), Net (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Feb. 28, 2017	Feb. 29, 2016	Feb. 28, 2017	Feb. 29, 2016
Other Income And Expenses [Abstract]
Interest (income)	$ (1,599)	$ (2,019)	$ (3,832)	$ (4,602)
Net (gain) on sale of marketable securities	(1,640)	(1,020)	(5,338)	(5,438)
Other-than-temporary impairment on securities	17	839	420	3,312
Dividend (income)	(405)	(709)	(1,131)	(1,349)
Investment (income), net	$ (3,627)	$ (2,909)	$ (9,881)	$ (8,077)