10. STOCKHOLDERS' EQUITY, COMPREHENSIVE INCOME AND STOCK-BASED COMPENSATION (Details 5) - Stock Option - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	May 31, 2018	May 31, 2017	May 31, 2016
Options Outstanding, Beginning	3,074,000	3,201,000	3,686,000
Options Granted	338,000	368,000	92,000
Options terminated	(16,000)	(55,000)	(329,000)
Options exercised	(537,000)	(440,000)	(248,000)
Number of Options Outstanding, Ending	2,859,000	3,074,000	3,201,000
Options fully vested and expected to vest	2,825,000
Weighted Average Exercise Price Outstanding, Beginning	$ 1.73	$ 1.66	$ 1.66
Weighted Average Exercise Price Granted	3.56	1.83	2.12
Weighted Average Exercise Price Terminated	2.72	1.42	1.93
Weighted Average Exercise Price Exercised	1.17	1.35	1.34
Weighted Average Exercise Price Outstanding, Ending	2.04	$ 1.73	$ 1.66
Weighted Average Exercise Price fully vested and expected to vest	$ 2.04
Aggregate Intrinsic Value, beginning balance	$ 8,763	$ 189	$ 2,946
Aggregate Intrinsic Value, ending balance	1,987	$ 8,763	$ 189
Aggregate Intrinsic Value for Options fully vested and expected to vest	$ 1,976