2. STOCK-BASED COMPENSATION - Options outstanding and exercisable (Details 4) $ / shares in Units, $ in Thousands	9 Months Ended
	Feb. 28, 2017 USD ($) $ / shares shares
$0.59-$0.97
Options Outstanding, Ending (in thousands) | shares	514
Weighted Average Remaining Contractual Life (Years) Options Outstanding	2 years 11 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 11 days
Weighted Average Exercise Price for Options exercisable, ending | $ / shares	$ .66
$1.09-$1.40
Options Outstanding, Ending (in thousands) | shares	847
Weighted Average Remaining Contractual Life (Years) Options Outstanding	2 years 7 months 28 days
Weighted Average Exercise Price Outstanding, Ending | $ / shares	$ 1.28
Options exercisable shares, ending (in thousands) | shares	796
Weighted Average Remaining Contractual Life (Years) Options Exercisable	2 years 7 months 6 days
Weighted Average Exercise Price for Options exercisable, ending | $ / shares	$ 1.28
$1.68-$2.06
Options Outstanding, Ending (in thousands) | shares	546
Weighted Average Remaining Contractual Life (Years) Options Outstanding	5 years 4 months 17 days
Weighted Average Exercise Price Outstanding, Ending | $ / shares	$ 1.77
Options exercisable shares, ending (in thousands) | shares	264
Weighted Average Remaining Contractual Life (Years) Options Exercisable	4 years 4 months 24 days
Weighted Average Exercise Price for Options exercisable, ending | $ / shares	$ 1.86
$2.10-$2.81
Options Outstanding, Ending (in thousands) | shares	1,250
Weighted Average Remaining Contractual Life (Years) Options Outstanding	4 years 9 months 11 days
Weighted Average Exercise Price Outstanding, Ending | $ / shares	$ 2.44
Options exercisable shares, ending (in thousands) | shares	792
Weighted Average Remaining Contractual Life (Years) Options Exercisable	4 years 8 months 5 days
Weighted Average Exercise Price for Options exercisable, ending | $ / shares	$ 2.45
$0.59-$2.81
Options Outstanding, Ending (in thousands) | shares	3,157
Weighted Average Remaining Contractual Life (Years) Options Outstanding	3 years 10 months 13 days
Weighted Average Exercise Price Outstanding, Ending | $ / shares	$ 1.72
Options exercisable shares, ending (in thousands) | shares	2,366
Weighted Average Remaining Contractual Life (Years) Options Exercisable	3 years 4 months 13 days
Weighted Average Exercise Price for Options exercisable, ending | $ / shares	$ 1.60
Aggregate Intrinsic Value for Options exercisable, ending | $	$ 8,608