TERM LOAN PAYABLE (Details) - USD ($)
$ / shares in Units, $ in Thousands
 1 Months Ended 2 Months Ended 12 Months Ended
Aug. 28, 2012
Mar. 31, 2015
Sep. 30, 2014
Aug. 31, 2014
Feb. 28, 2014
Jan. 31, 2014
Feb. 28, 2013
Oct. 31, 2012
Aug. 31, 2012
Dec. 31, 2014
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2016
Loan and Security Agreements                          
Maximum borrowing capacity $ 1,000                        
Proceeds from notes payable, net of original note payoff                       $ 7,056  
Exercise price of warrant (in dollars per share)                         $ 12.27
Gain on extinguishment                     $ 91    
Common stock warrant, Silicon Valley Bank, Original Term Loan                          
Loan and Security Agreements                          
Common stock that may be purchased upon exercise of warrant (in shares) 11,850                        
Exercise price of warrant (in dollars per share) $ 0.07                        
Common stock warrant, Silicon Valley Bank, Term Loan, Amendment No. 1                          
Loan and Security Agreements                          
Common stock that may be purchased upon exercise of warrant (in shares)         14,430                
Exercise price of warrant (in dollars per share)         $ 0.05                
Common stock warrant, Silicon Valley Bank, Term Loan, Amendment No. 2                          
Loan and Security Agreements                          
Common stock that may be purchased upon exercise of warrant (in shares)       86,580                  
Exercise price of warrant (in dollars per share)       $ 0.05                  
Series D convertible redeemable preferred stock                          
Loan and Security Agreements                          
Public offering of common stock, net of issuance costs, shares   4,166,667                      
6.0% Convertible promissory notes                          
Loan and Security Agreements                          
Gain on extinguishment   $ 91                      
6.0% Convertible promissory notes | Bridge Notes Purchase Agreement | Investors                          
Loan and Security Agreements                          
Amount issued                   $ 5,000      
Stated interest rate                   6.00%      
Term loan | Silicon Valley Bank loan agreement                          
Loan and Security Agreements                          
Maximum borrowing capacity $ 1,000                        
Amount borrowed             $ 500 $ 250 $ 250        
Initial period of interest only payments 12 months                        
Subsequent period of principal and interest payments 36 months                        
Term loan | Silicon Valley Bank loan agreement | Prime                          
Loan and Security Agreements                          
Variable interest rate margin (as a percent)                     2.25% 2.25%  
Interest rate (as a percent) 5.50%                        
Term loan | Silicon Valley Bank loan agreement, Amendment No. 1                          
Loan and Security Agreements                          
Maximum borrowing capacity           $ 6,000              
Amount borrowed         $ 2,000                
Proceeds from notes payable, net of original note payoff         $ 1,056                
Initial period of interest only payments         12 months                
Subsequent period of principal and interest payments         36 months                
Term loan | Silicon Valley Bank loan agreement, Amendment No. 1 | Prime                          
Loan and Security Agreements                          
Variable rate basis           1.75%              
Interest rate (as a percent)         5.00%                
Term loan | Silicon Valley Bank loan agreement Amendment No. 2                          
Loan and Security Agreements                          
Maximum borrowing capacity       $ 8,000                  
Amount borrowed     $ 3,000 $ 3,000                  
Initial period of interest only payments       12 months                  
Subsequent period of principal and interest payments       36 months                  
Term loan | Silicon Valley Bank loan agreement Amendment No. 2 | Prime                          
Loan and Security Agreements                          
Interest rate (as a percent)       5.00%