Investment (Income), Net (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Nov. 30, 2017	Nov. 30, 2016	Nov. 30, 2017	Nov. 30, 2016
Other Income And Expenses [Abstract]
Interest (income)	$ (1,297)	$ (1,093)	$ (2,191)	$ (2,233)
Net (gain) on sale of marketable securities	(2,037)	(1,114)	(4,897)	(3,698)
Other-than-temporary impairment on securities		217		403
Dividend (income)	(405)	(426)	(1,104)	(726)
Investment (income), net	$ (3,739)	$ (2,416)	$ (8,192)	$ (6,254)