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1. ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 4) - Employee Stock Purchase Plan - $ / shares
12 Months Ended
May 31, 2017
May 31, 2016
May 31, 2015
Minimum      
Fair Value Assumptions for ESPP purchase rights granted      
Expected term (in years) 6 months 6 months 6 months
Volatility 79.00% 64.00% 55.00%
Risk-free interest rates 0.48% 0.40% 0.04%
Weighted Average Grant Date Fair Value $ 1.65 $ 0.80 $ 1.43
Maximum      
Fair Value Assumptions for ESPP purchase rights granted      
Expected term (in years) 2 years 2 years 2 years
Volatility 108.00% 74.00% 83.00%
Risk-free interest rates 0.80% 0.76% 0.55%
Weighted Average Grant Date Fair Value $ 1.65 $ 0.80 $ 1.43