11. STOCKHOLDERS' EQUITY AND STOCK-BASED COMPENSATION (Details 3) - shares	12 Months Ended
	May 31, 2021	May 31, 2020	May 31, 2019
RSUs granted (in thousands)	(170)	(10)	0
Shares withheld for taxes and not issued (in thousands)	9	6
Stock Option and RSU Transactions
Available shares, beginning (in thousands)	1,650	1,147	1,812
Additional shares reserved (in thousands)		1,196
Options granted (in thousands)	(297)	(738)	(804)
RSUs granted (in thousands)	(340)	(25)
RSUs cancelled (in thousands)	1		8
Shares withheld for taxes and not issued (in thousands)	9	6
Options terminated (in thousands)	455	457	195
Options expired (in thousands)	(341)	(393)	(64)
Available shares, ending (in thousands)	1,137	1,650	1,147