Quarterly report pursuant to Section 13 or 15(d)

STOCKHOLDERS' EQUITY - Warrant (Details)

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STOCKHOLDERS' EQUITY - Warrant (Details) - USD ($)
$ / shares in Units, $ in Millions
Jun. 19, 2017
Mar. 31, 2019
Dec. 31, 2018
Sep. 19, 2018
Jul. 25, 2017
Jun. 30, 2017
Class of Warrant or Right [Line Items]            
Common stock, par value (in dollars per share)   $ 0.0001 $ 0.0001      
Common stock, shares issued (in shares)   27,595,840 27,568,656      
Common Stock Warrant            
Class of Warrant or Right [Line Items]            
Common stock, par value (in dollars per share) $ 0.0001          
Right to acquire variable amount of common stock, term 15 months          
Common Stock Warrant | Soryn HLDR            
Class of Warrant or Right [Line Items]            
Exercise price (in dollars per share) $ 3.18          
Term of warrant 3 years          
Changes in warrant liability $ 3.3          
Common Stock | Common Stock Warrant | Soryn HLDR            
Class of Warrant or Right [Line Items]            
Common stock warrant purchased (in shares) 2,000,000 2,355,506        
Common stock, shares issued (in shares) 2,000,000       46,370 309,136
Changes in warrant liability       $ 4.5