2. STOCK-BASED COMPENSATION (Details 4) $ / shares in Units, $ in Thousands	6 Months Ended
	Nov. 30, 2017 USD ($) $ / shares shares
$0.59-$0.97
Options Outstanding, Ending (in thousands) | shares	424
Weighted Average Remaining Contractual Life (Years) Options Outstanding	1 year 3 months 22 days
Weighted Average Exercise Price Outstanding, Ending | $ / shares	$ 0.68
Options exercisable shares, ending (in thousands) | shares	424
Weighted Average Remaining Contractual Life (Years) Options Exercisable	1 year 3 months 22 days
Weighted Average Exercise Price for Options exercisable, ending | $ / shares	$ 0.68
$1.09-$1.36
Options Outstanding, Ending (in thousands) | shares	645
Weighted Average Remaining Contractual Life (Years) Options Outstanding	2 years 1 month 10 days
Weighted Average Exercise Price Outstanding, Ending | $ / shares	$ 1.27
Options exercisable shares, ending (in thousands) | shares	645
Weighted Average Remaining Contractual Life (Years) Options Exercisable	2 years 1 month 6 days
Weighted Average Exercise Price for Options exercisable, ending | $ / shares	$ 1.27
$1.68-$2.06
Options Outstanding, Ending (in thousands) | shares	487
Weighted Average Remaining Contractual Life (Years) Options Outstanding	4 years 8 months 23 days
Weighted Average Exercise Price Outstanding, Ending | $ / shares	$ 1.74
Options exercisable shares, ending (in thousands) | shares	276
Weighted Average Remaining Contractual Life (Years) Options Exercisable	4 years 11 days
Weighted Average Exercise Price for Options exercisable, ending | $ / shares	$ 1.79
$2.10-$2.81
Options Outstanding, Ending (in thousands) | shares	1,197
Weighted Average Remaining Contractual Life (Years) Options Outstanding	4 years 4 days
Weighted Average Exercise Price Outstanding, Ending | $ / shares	$ 2.45
Options exercisable shares, ending (in thousands) | shares	953
Weighted Average Remaining Contractual Life (Years) Options Exercisable	3 years 11 months 26 days
Weighted Average Exercise Price for Options exercisable, ending | $ / shares	$ 2.47
$3.46-$3.93
Options Outstanding, Ending (in thousands) | shares	265
Weighted Average Remaining Contractual Life (Years) Options Outstanding	6 years 7 months 28 days
Weighted Average Exercise Price Outstanding, Ending | $ / shares	$ 3.88
Options exercisable shares, ending (in thousands) | shares	22
Weighted Average Remaining Contractual Life (Years) Options Exercisable	6 years 7 months 28 days
Weighted Average Exercise Price for Options exercisable, ending | $ / shares	$ 3.88
$0.59-$3.93
Options Outstanding, Ending (in thousands) | shares	3,018
Weighted Average Remaining Contractual Life (Years) Options Outstanding	3 years 6 months 25 days
Weighted Average Exercise Price Outstanding, Ending | $ / shares	$ 1.96
Options exercisable shares, ending (in thousands) | shares	2,320
Weighted Average Remaining Contractual Life (Years) Options Exercisable	3 years
Weighted Average Exercise Price for Options exercisable, ending | $ / shares	$ 1.74
Aggregate Intrinsic Value for Options exercisable, ending | $	$ 1,985