10. STOCKHOLDERS' EQUITY, COMPREHENSIVE INCOME AND STOCK-BASED COMPENSATION (Details 5) - Outstanding Options Stock Option Transactions - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	May 31, 2019	May 31, 2018	May 31, 2017
Options Outstanding, Beginning (in thousands)	2,859	3,074	3,201
Options Granted (in thousands)	804	338	368
Options terminated (in thousands)	(195)	(16)	(55)
Options exercised (in thousands)	(361)	(537)	(440)
Options Outstanding, Ending (in thousands)	3,107	2,859	3,074
Options fully vested and expected to vest (in thousands)	3,079
Weighted Average Exercise Price Outstanding, Beginning	$ 2.04	$ 1.73	$ 1.66
Weighted Average Exercise Price Granted	2.19	3.56	1.83
Weighted Average Exercise Price Terminated	2.32	2.72	1.42
Weighted Average Exercise Price Exercised	0.85	1.17	1.35
Weighted Average Exercise Price Outstanding, Ending	2.20	$ 2.04	$ 1.73
Weighted Average Exercise Price fully vested and expected to vest	$ 2.20
Aggregate Intrinsic Value, beginning balance	$ 1,987	$ 8,763	$ 189
Aggregate Intrinsic Value, ending balance	283	$ 1,987	$ 8,763
Aggregate Intrinsic Value for Options fully vested and expected to vest	$ 282