2. STOCK-BASED COMPENSATION - Options outstanding and exercisable (Details 4) $ / shares in Units, $ in Thousands	3 Months Ended
	Aug. 31, 2016 USD ($) $ / shares shares
Range Exercise Prices Options Outstanding Minimum	$ .59
Range Exercise Prices Options Outstanding Maximum	$ 2.71
Options Outstanding, Ending (in thousands) | shares	3,382
Weighted Average Remaining Contractual Life (Years) Options Outstanding	4 years 2 months 16 days
Weighted Average Exercise Price Outstanding, Ending	$ 1.67
Options exercisable shares, ending (in thousands) | shares	2,379
Weighted Average Remaining Contractual Life (Years) Options Exercisable	3 years 7 months 10 days
Weighted Average Exercise Price for Options exercisable, ending	$ 1.52
Aggregate Intrinsic Value for Options exercisable, ending | $	$ 2,235
Options Price Range A
Range Exercise Prices Options Outstanding Minimum	$ .59
Range Exercise Prices Options Outstanding Maximum	$ .97
Options Outstanding, Ending (in thousands) | shares	565
Weighted Average Remaining Contractual Life (Years) Options Outstanding	2 years 6 months 25 days
Weighted Average Exercise Price Outstanding, Ending	$ .68
Options exercisable shares, ending (in thousands) | shares	565
Weighted Average Remaining Contractual Life (Years) Options Exercisable	2 years 6 months 25 days
Weighted Average Exercise Price for Options exercisable, ending	$ .68
Options Price Range B
Range Exercise Prices Options Outstanding Minimum	1.09
Range Exercise Prices Options Outstanding Maximum	$ 1.40
Options Outstanding, Ending (in thousands) | shares	1,039
Weighted Average Remaining Contractual Life (Years) Options Outstanding	3 years 11 days
Weighted Average Exercise Price Outstanding, Ending	$ 1.28
Options exercisable shares, ending (in thousands) | shares	923
Weighted Average Remaining Contractual Life (Years) Options Exercisable	2 years 10 months 28 days
Weighted Average Exercise Price for Options exercisable, ending	$ 1.28
Options Price Range C
Range Exercise Prices Options Outstanding Minimum	1.68
Range Exercise Prices Options Outstanding Maximum	$ 2.06
Options Outstanding, Ending (in thousands) | shares	548
Weighted Average Remaining Contractual Life (Years) Options Outstanding	5 years 10 months 17 days
Weighted Average Exercise Price Outstanding, Ending	$ 1.77
Options exercisable shares, ending (in thousands) | shares	215
Weighted Average Remaining Contractual Life (Years) Options Exercisable	4 years 7 months 6 days
Weighted Average Exercise Price for Options exercisable, ending	$ 1.90
Options Price Range D
Range Exercise Prices Options Outstanding Minimum	2.10
Range Exercise Prices Options Outstanding Maximum	$ 2.71
Options Outstanding, Ending (in thousands) | shares	1,230
Weighted Average Remaining Contractual Life (Years) Options Outstanding	5 years 2 months 12 days
Weighted Average Exercise Price Outstanding, Ending	$ 2.43
Options exercisable shares, ending (in thousands) | shares	676
Weighted Average Remaining Contractual Life (Years) Options Exercisable	5 years 1 month 13 days
Weighted Average Exercise Price for Options exercisable, ending	$ 2.45