2. STOCK-BASED COMPENSATION - Options outstanding and exercisable (Details 4) (USD $) In Thousands, except Share data, unless otherwise specified	6 Months Ended
	Nov. 30, 2014	Aug. 31, 2014	May 31, 2014
Number of Options Outstanding, Ending (in thousands)	3,418	3,323	3,002
Weighted Average Exercise Price Outstanding, Ending	$ 1.61	$ 1.59	$ 1.31
Options exercisable shares, ending (in thousands)	1,928
Weighted Average Exercise Price for Options exercisable, ending	$ 1.29
Options exercisable at November 30, 2014 Aggregate intrinsic value	$ 2,435
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)	680
Weighted Average Remaining Contractual Life (Years) Options Outstanding	4 years 4 months 2 days
Weighted Average Exercise Price Outstanding, Ending	$ 0.70
Options exercisable shares, ending (in thousands)	561
Weighted Average Remaining Contractual Life (Years) Options Exercisable	4 years 4 months 20 days
Weighted Average Exercise Price for Options exercisable, ending	$ 0.72
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)	1,327
Weighted Average Remaining Contractual Life (Years) Options Outstanding	4 years 5 months 19 days
Weighted Average Exercise Price Outstanding, Ending	$ 1.28
Options exercisable shares, ending (in thousands)	737
Weighted Average Remaining Contractual Life (Years) Options Exercisable	4 years 22 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)	547
Weighted Average Remaining Contractual Life (Years) Options Outstanding	3 years 6 months 29 days
Weighted Average Exercise Price Outstanding, Ending	$ 1.92
Options exercisable shares, ending (in thousands)	372
Weighted Average Remaining Contractual Life (Years) Options Exercisable	2 years 2 months 16 days
Weighted Average Exercise Price for Options exercisable, ending	$ 1.91
Options Price Range D
Range Exercise Prices Options Outstanding Minimum	$ 2.15
Range Exercise Prices Options Outstanding Maximum	$ 2.71
Number of Options Outstanding, Ending (in thousands)	864
Weighted Average Remaining Contractual Life (Years) Options Outstanding	6 years 2 months 5 days
Weighted Average Exercise Price Outstanding, Ending	$ 2.63
Options exercisable shares, ending (in thousands)	258
Weighted Average Remaining Contractual Life (Years) Options Exercisable	4 years 11 months 26 days
Weighted Average Exercise Price for Options exercisable, ending	$ 1.68
Options Price Range E
Range Exercise Prices Options Outstanding Minimum	$ 0.59
Range Exercise Prices Options Outstanding Maximum	$ 2.71
Number of Options Outstanding, Ending (in thousands)	3,418
Weighted Average Remaining Contractual Life (Years) Options Outstanding	4 years 8 months 27 days
Weighted Average Exercise Price Outstanding, Ending	$ 1.61
Options exercisable shares, ending (in thousands)	1,928
Weighted Average Remaining Contractual Life (Years) Options Exercisable	3 years 11 months 1 day
Weighted Average Exercise Price for Options exercisable, ending	$ 1.29