11. STOCKHOLDERS' EQUITY AND STOCK-BASED COMPENSATION (Details 4) - Outstanding Options Stock Option Transactions - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	May 31, 2021	May 31, 2020	May 31, 2019
Options outstanding, beginning (in thousands)	3,153	3,107	2,859
Options granted (in thousands)	297	738	804
Options terminated (in thousands)	(455)	(457)	(195)
Options exercised (in thousands)	(229)	(235)	(361)
Options outstanding, ending (in thousands)	2,766	3,153	3,107
Options fully vested and expected to vest (in thousands)	2,732
Weighted average exercise price outstanding, beginning	$ 2.17	$ 2.20	$ 2.04
Weighted average exercise price granted	1.78	1.61	2.19
Weighted average exercise price terminated	2.31	1.98	2.32
Weighted average exercise price exercised	1.54	1.22	0.85
Weighted average exercise price outstanding, ending	2.16	$ 2.17	$ 2.20
Weighted average exercise price fully vested and expected to vest	$ 2.16
Aggregate intrinsic value, beginning	$ 102	$ 283	$ 1,987
Aggregate intrinsic value, ending	807	$ 102	$ 283
Aggregate intrinsic value for options fully vested and expected to vest	$ 795