11. STOCKHOLDERS' EQUITY, COMPREHENSIVE INCOME AND STOCK-BASED COMPENSATION (Details 4) - Outstanding Options Stock Option Transactions - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	May 31, 2020	May 31, 2019	May 31, 2018
Options outstanding, beginning (in thousands)	3,107	2,859	3,074
Options granted (in thousands)	738	804	338
Options terminated (in thousands)	(457)	(195)	(16)
Options exercised (in thousands)	(235)	(361)	(537)
Options outstanding, ending (in thousands)	3,153	3,107	2,859
Options fully vested and expected to vest (in thousands)	3,115
Weighted average exercise price outstanding, beginning	$ 2.20	$ 2.04	$ 1.73
Weighted average exercise price granted	1.61	2.19	3.56
Weighted average exercise price terminated	1.98	2.32	2.72
Weighted average exercise price exercised	1.22	0.85	1.17
Weighted average exercise price outstanding, ending	2.17	$ 2.20	$ 2.04
Weighted average exercise price fully vested and expected to vest	$ 2.17
Aggregate intrinsic value, beginning	$ 283	$ 1,987	$ 8,763
Aggregate intrinsic value, ending	102	$ 283	$ 1,987
Aggregate intrinsic value for options fully vested and expected to vest	$ 101