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2. STOCK-BASED COMPENSATION - Options (Details 1) (Stock Options, USD $)
3 Months Ended 9 Months Ended
Feb. 28, 2013
Feb. 28, 2014
Feb. 28, 2013
Stock Options
     
Expected term (in years) 5 years 4 years 5 years
Volatility 94.00% 95.00% 91.00%
Expected dividend $ 0 $ 0 $ 0
Risk-free interest rates 0.76% 1.40% 0.72%
Estimated forfeiture rate 0.25% 0.25% 0.25%
Weighted average grant date fair value $ 0.62 $ 1.03 $ 0.78