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SHARE-BASED COMPENSATION - Weighted-Average Inputs and Assumptions (Details) - $ / shares
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Share-based Payment Arrangement [Abstract]      
Fair value of common stock (in dollars per share) $ 1.02 $ 1.71 $ 1.74
Exercise price of the option (in dollars per share) $ 1.02 $ 1.71 $ 1.74
Expected term (years) 5 years 11 months 23 days 5 years 11 months 21 days 5 years 6 months 32 days
Risk-free interest rate 2.10% 2.80% 1.90%
Expected volatility 78.10% 74.20% 81.60%
Dividend yield 0.00% 0.00% 0.00%