2. STOCK-BASED COMPENSATION - Options outstanding and exercisable (Details 4) $ / shares in Units, $ in Thousands	6 Months Ended
	Nov. 30, 2016 USD ($) $ / shares shares
$0.59-$0.97
Options Outstanding, Ending (in thousands) | shares	514
Weighted Average Remaining Contractual Life (Years) Options Outstanding	2 years 7 months 7 days
Weighted Average Exercise Price Outstanding, Ending | $ / shares	$ .66
Options exercisable shares, ending (in thousands) | shares	514
Weighted Average Remaining Contractual Life (Years) Options Exercisable	2 years 7 months 7 days
Weighted Average Exercise Price for Options exercisable, ending | $ / shares	$ .66
$1.09-$1.40
Options Outstanding, Ending (in thousands) | shares	899
Weighted Average Remaining Contractual Life (Years) Options Outstanding	2 years 10 months 13 days
Weighted Average Exercise Price Outstanding, Ending | $ / shares	$ 1.28
Options exercisable shares, ending (in thousands) | shares	816
Weighted Average Remaining Contractual Life (Years) Options Exercisable	2 years 9 months 7 days
Weighted Average Exercise Price for Options exercisable, ending | $ / shares	$ 1.28
$1.68-$2.06
Options Outstanding, Ending (in thousands) | shares	547
Weighted Average Remaining Contractual Life (Years) Options Outstanding	5 years 7 months 17 days
Weighted Average Exercise Price Outstanding, Ending | $ / shares	$ 1.77
Options exercisable shares, ending (in thousands) | shares	240
Weighted Average Remaining Contractual Life (Years) Options Exercisable	4 years 6 months 7 days
Weighted Average Exercise Price for Options exercisable, ending | $ / shares	$ 1.88
$2.10-$2.81
Options Outstanding, Ending (in thousands) | shares	1,269
Weighted Average Remaining Contractual Life (Years) Options Outstanding	5 years 11 days
Weighted Average Exercise Price Outstanding, Ending | $ / shares	$ 2.44
Options exercisable shares, ending (in thousands) | shares	738
Weighted Average Remaining Contractual Life (Years) Options Exercisable	4 years 10 months 24 days
Weighted Average Exercise Price for Options exercisable, ending | $ / shares	$ 2.45
$0.59-$2.81
Options Outstanding, Ending (in thousands) | shares	3,229
Weighted Average Remaining Contractual Life (Years) Options Outstanding	4 years 29 days
Weighted Average Exercise Price Outstanding, Ending | $ / shares	$ 1.72
Options exercisable shares, ending (in thousands) | shares	2,308
Weighted Average Remaining Contractual Life (Years) Options Exercisable	3 years 6 months 7 days
Weighted Average Exercise Price for Options exercisable, ending | $ / shares	$ 1.58
Aggregate Intrinsic Value for Options exercisable, ending | $	$ 3,261