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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - STOCK OPTIONS AND EMLOYEE STOCK PURCHASE PLAN (Details)
3 Months Ended
Mar. 03, 2015
Mar. 31, 2016
Mar. 31, 2015
Stock-Based Compensation      
Original exercise period for vested outstanding awards after termination 90 days    
Modified exercise period for vested outstanding awards after termination 1 year    
Stock options      
Stock-Based Compensation      
Vesting period of awards   4 years  
Assumptions used to estimate fair value of awards      
Dividend yield (as a percent)   0.00% 0.00%
Expected volatility (as a percent)   89.00% 88.40%
Risk-free interest rate (as a percent)   1.21% 1.70%
Expected term   5 years 6 months 5 years 6 months
Employee Stock Purchase Plan      
Assumptions used to estimate fair value of awards      
Dividend yield (as a percent)   0.00% 0.00%
Expected volatility (as a percent)   68.40%  
Expected volatility range, minimum (as a percent)     72.10%
Expected volatility range, maximum (as a percent)     139.20%
Risk-free interest rate (as a percent)   0.28%  
Risk-free interest rate range, minimum (as a percent)     0.11%
Risk-free interest rate range, maximum (as a percent)     0.25%
Expected term   12 months  
Employee Stock Purchase Plan | Minimum      
Assumptions used to estimate fair value of awards      
Expected term     6 months
Employee Stock Purchase Plan | Maximum      
Assumptions used to estimate fair value of awards      
Expected term     12 months
Service-based restricted stock awards      
Stock-Based Compensation      
Vesting period of awards   4 years