2. STOCK-BASED COMPENSATION (Details 4) $ / shares in Units, $ in Thousands	9 Months Ended
	Feb. 28, 2018 USD ($) $ / shares shares
$0.59-$0.97
Options Outstanding, Ending (in thousands) | shares	324
Weighted Average Remaining Contractual Life (Years) Options Outstanding	1 year 7 days
Weighted Average Exercise Price Outstanding, Ending | $ / shares	$ 0.66
Options exercisable shares, ending (in thousands) | shares	324
Weighted Average Remaining Contractual Life (Years) Options Exercisable	1 year 7 days
Weighted Average Exercise Price for Options exercisable, ending | $ / shares	$ 0.66
$1.09-$1.36
Options Outstanding, Ending (in thousands) | shares	605
Weighted Average Remaining Contractual Life (Years) Options Outstanding	1 year 10 months 17 days
Weighted Average Exercise Price Outstanding, Ending | $ / shares	$ 1.28
Options exercisable shares, ending (in thousands) | shares	605
Weighted Average Remaining Contractual Life (Years) Options Exercisable	1 year 10 months 17 days
Weighted Average Exercise Price for Options exercisable, ending | $ / shares	$ 1.28
$1.68-$2.06
Options Outstanding, Ending (in thousands) | shares	486
Weighted Average Remaining Contractual Life (Years) Options Outstanding	4 years 5 months 23 days
Weighted Average Exercise Price Outstanding, Ending | $ / shares	$ 1.74
Options exercisable shares, ending (in thousands) | shares	295
Weighted Average Remaining Contractual Life (Years) Options Exercisable	3 years 10 months 20 days
Weighted Average Exercise Price for Options exercisable, ending | $ / shares	$ 1.79
$2.10-$2.81
Options Outstanding, Ending (in thousands) | shares	1,204
Weighted Average Remaining Contractual Life (Years) Options Outstanding	3 years 9 months 15 days
Weighted Average Exercise Price Outstanding, Ending | $ / shares	$ 2.45
Options exercisable shares, ending (in thousands) | shares	1,012
Weighted Average Remaining Contractual Life (Years) Options Exercisable	3 years 8 months 27 days
Weighted Average Exercise Price for Options exercisable, ending | $ / shares	$ 2.47
$3.46-$3.93
Options Outstanding, Ending (in thousands) | shares	264
Weighted Average Remaining Contractual Life (Years) Options Outstanding	6 years 4 months 28 days
Weighted Average Exercise Price Outstanding, Ending | $ / shares	$ 3.86
Options exercisable shares, ending (in thousands) | shares	46
Weighted Average Remaining Contractual Life (Years) Options Exercisable	6 years 5 months 12 days
Weighted Average Exercise Price for Options exercisable, ending | $ / shares	$ 3.79
$0.59-$3.93
Options Outstanding, Ending (in thousands) | shares	2,883
Weighted Average Remaining Contractual Life (Years) Options Outstanding	3 years 5 months 5 days
Weighted Average Exercise Price Outstanding, Ending | $ / shares	$ 2.01
Options exercisable shares, ending (in thousands) | shares	2,282
Weighted Average Remaining Contractual Life (Years) Options Exercisable	2 years 11 months 5 days
Weighted Average Exercise Price for Options exercisable, ending | $ / shares	$ 1.83
Aggregate Intrinsic Value for Options exercisable, ending | $	$ 1,351