STOCKHOLDERS' EQUITY - Common Stock Warrants (Details) $ / shares in Units, $ in Millions	Feb. 27, 2015 shares	Apr. 02, 2014 USD ($) shares	Apr. 02, 2014 USD ($) shares	Dec. 31, 2015 $ / shares shares
Class of Warrant or Right [Line Items]
Convertible preferred stock warrant liability | $		$ 0.6	$ 0.6
Series B Convertible Preferred Stock Warrants
Class of Warrant or Right [Line Items]
Conversion to common stock warrants, conversion ratio			1.1228
Series C Convertible Preferred Stock Warrants
Class of Warrant or Right [Line Items]
Conversion to common stock warrants, conversion ratio		1
Series E Convertible Preferred Stock Warrants
Class of Warrant or Right [Line Items]
Conversion to common stock warrants, conversion ratio			1
Convertible Preferred Stock
Class of Warrant or Right [Line Items]
Number of shares called by warrant		103,034	103,034
Common Stock
Class of Warrant or Right [Line Items]
Number of shares called by warrant		107,876	107,876
Common Stock | Series B And Series C Common Stock Warrants
Class of Warrant or Right [Line Items]
Warrants extension term	1 year
Number of warrants with extension term	73,883
Number of warrants expired				33,993
Common Stock | Series B Common Stock Warrants
Class of Warrant or Right [Line Items]
Convertible preferred stock warrants outstanding				44,280
Exercise price (in dollars per share) | $ / shares				$ 4.057
Common Stock | Series C Common Stock Warrants
Class of Warrant or Right [Line Items]
Convertible preferred stock warrants outstanding				29,603
Exercise price (in dollars per share) | $ / shares				$ 2.768