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2. STOCK-BASED COMPENSATION - Fair values of the ESPP shares (Details 2) (Employee Stock Purchase Plan, USD $)
3 Months Ended 6 Months Ended
Nov. 30, 2013
Nov. 30, 2013
Volatility, Minimum 86.00% 86.00%
Volatility, Maximum 100.00% 100.00%
Expected dividend $ 0 $ 0
Risk-free interest rates, Minimum 0.04% 0.04%
Risk-free interest rates, Maximum 0.33% 0.33%
Estimated forfeiture rate 0.00% 0.00%
Weighted average grant date fair value $ 1.34 $ 1.34
Minimum
   
Expected term (in years) 6 months 6 months
Maximum
   
Expected term (in years) 2 years 2 years