2. STOCK-BASED COMPENSATION - Options outstanding and exercisable (Details 4) $ / shares in Units, $ in Thousands	6 Months Ended
	Nov. 30, 2015 USD ($) $ / shares shares
Range Exercise Prices Options Outstanding Minimum	$ 0.59
Range Exercise Prices Options Outstanding Maximum	$ 2.71
Number of Options Outstanding, Ending (in thousands) | shares	3,385
Weighted Average Remaining Contractual Life (Years) Options Outstanding	4 years 6 months 29 days
Weighted Average Exercise Price Outstanding, Ending	$ 1.67
Options exercisable shares, ending (in thousands) | shares	2,238
Weighted Average Remaining Contractual Life (Years) Options Exercisable	4 years 29 days
Weighted Average Exercise Price for Options exercisable, ending	$ 1.47
Aggregate Intrinsic Value for Options exercisable, ending | $	$ 1,416
Options Price Range A
Range Exercise Prices Options Outstanding Minimum	$ 0.59
Range Exercise Prices Options Outstanding Maximum	$ 0.97
Number of Options Outstanding, Ending (in thousands) | shares	578
Weighted Average Remaining Contractual Life (Years) Options Outstanding	3 years 3 months 22 days
Weighted Average Exercise Price Outstanding, Ending	$ .68
Options exercisable shares, ending (in thousands) | shares	561
Weighted Average Remaining Contractual Life (Years) Options Exercisable	3 years 3 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
Number of Options Outstanding, Ending (in thousands) | shares	1,222
Weighted Average Remaining Contractual Life (Years) Options Outstanding	3 years 7 months 2 days
Weighted Average Exercise Price Outstanding, Ending	$ 1.28
Options exercisable shares, ending (in thousands) | shares	945
Weighted Average Remaining Contractual Life (Years) Options Exercisable	3 years 4 months 17 days
Weighted Average Exercise Price for Options exercisable, ending	$ 1.28
Options Price Range C
Range Exercise Prices Options Outstanding Minimum	1.73
Range Exercise Prices Options Outstanding Maximum	$ 2.06
Number of Options Outstanding, Ending (in thousands) | shares	267
Weighted Average Remaining Contractual Life (Years) Options Outstanding	5 years 2 months 5 days
Weighted Average Exercise Price Outstanding, Ending	$ 1.88
Options exercisable shares, ending (in thousands) | shares	228
Weighted Average Remaining Contractual Life (Years) Options Exercisable	5 years 3 months
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
Number of Options Outstanding, Ending (in thousands) | shares	1,318
Weighted Average Remaining Contractual Life (Years) Options Outstanding	5 years 11 months 5 days
Weighted Average Exercise Price Outstanding, Ending	$ 2.43
Options exercisable shares, ending (in thousands) | shares	504
Weighted Average Remaining Contractual Life (Years) Options Exercisable	5 years 8 months 12 days
Weighted Average Exercise Price for Options exercisable, ending	$ 2.49