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STOCK AWARD PLAN AND STOCK-BASED COMPENSATION - Summary of Assumptions Used in Black Scholes Model to Estimate Fair Value of Stock Options (Details) - $ / shares
9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Stock Award Plan and Stock-Based Compensation    
Dividend yield 0.00%  
Weighted average grant date fair value per share of common stock $ 5.08  
Employee Stock Option    
Stock Award Plan and Stock-Based Compensation    
Expected term (years) 5 years 6 months  
Dividend yield 0.00% 0.00%
Weighted average grant date fair value per share of common stock $ 3.26 $ 4.97
Employee Stock Option | Minimum    
Stock Award Plan and Stock-Based Compensation    
Expected term (years)   5 years 6 months
Risk free interest rate 1.91% 2.33%
Volatility 74.00% 76.00%
Employee Stock Option | Maximum    
Stock Award Plan and Stock-Based Compensation    
Expected term (years)   6 years 3 months
Risk free interest rate 1.96% 2.93%
Volatility 77.00% 83.00%
Non-Employees Stock Options    
Stock Award Plan and Stock-Based Compensation    
Dividend yield   0.00%
Weighted average reporting date fair value per share of common stock   $ 10.94
Non-Employees Stock Options | Minimum    
Stock Award Plan and Stock-Based Compensation    
Expected term (years)   7 years 10 months 24 days
Risk free interest rate   2.46%
Volatility   83.00%
Non-Employees Stock Options | Maximum    
Stock Award Plan and Stock-Based Compensation    
Expected term (years)   9 years 3 months 18 days
Risk free interest rate   3.04%
Volatility   88.00%