Net (Gain) on Marketable Securities (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Nov. 30, 2020	Nov. 30, 2019	Nov. 30, 2020	Nov. 30, 2019
(In thousands)
Unrealized (gains) on marketable equity securities	$ (7,863)	$ (7,062)	$ (21,819)	$ (10,538)
Realized (gains) losses on marketable equity securities	(548)	114	1,624	46
Realized losses on available-for-sale debt securities	23	9	23	13
Net (gain) on marketable securities	$ (8,388)	$ (6,939)	$ (20,172)	$ (10,479)