Investment (Income), Net (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Feb. 28, 2018	Feb. 28, 2017	Feb. 28, 2018	Feb. 28, 2017
Other Income And Expenses [Abstract]
Interest (income)	$ (1,454)	$ (1,599)	$ (3,645)	$ (3,832)
Net (gain) on sale of marketable securities	(1,935)	(1,640)	(6,833)	(5,338)
Other-than-temporary impairment on securities		17		420
Dividend (income)	(2,082)	(405)	(3,185)	(1,131)
Investment (income), net	$ (5,471)	$ (3,627)	$ (13,663)	$ (9,881)