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2. STOCK-BASED COMPENSATION - Fair values of the ESPP shares (Details 2) - Employee Stock Purchase Plan - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 6 Months Ended
Nov. 30, 2014
Nov. 30, 2014
Volatility, Minimum 55.00% 55.00%
Volatility, Maximum 83.00% 83.00%
Expected dividend $ 0 $ 0
Risk-free interest rates, Minimum 0.04% 0.04%
Risk-free interest rates, Maximum 0.53% 0.53%
Estimated forfeiture rate 0.00% 0.00%
Weighted average grant date fair value $ 1.47 $ 1.47
Minimum    
Expected term (in years) 6 months 6 months
Maximum    
Expected term (in years) 2 years 2 years