STOCKHOLDERS' EQUITY - Stock options (Details) - USD ($)
3 Months Ended 12 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Dec. 31, 2019
Dec. 31, 2018
STOCKHOLDERS' EQUITY        
Number of Options, Exercised   15,000    
Stock options [Member]        
STOCKHOLDERS' EQUITY        
Number of Options, Outstanding at Beginning of Year 4,197,000      
Number of Options, Grants 0      
Number of Options, Exercised 0      
Number of Option, Forfeited/cancelled/expired/settled 24,000      
Number of Options, Balance at End of Year 4,173,000   4,197,000  
Number of Options, Vested and expected to vest 4,170,000      
Number of Options, Unvested 17,000      
Number of Options, Exercisable 4,156,000      
Weighted-Average Exercise Price, Outstanding at Beginning of Year (in dollars per share) $ 2.13      
Weighted-Average Exercise Price, Grants (in dollars per share) 0.00      
Weighted-Average Exercise Price, Exercised (in dollars per share) 0.00      
Weighted-Average Exercise Price, Forfeited/cancelled/expired/settled (in dollars per share) 3.17      
Weighted-Average Exercise Price, Balance at End of Year (in dollars per share) 2.12   $ 2.13  
Weighted-Average Exercise Price, Vested and expected to vest (in dollars per share) 2.12      
Weighted-Average Exercise Price, Unvested (in dollars per share) 1.90      
Weighted-Average Exercise Price, Exercisable (in dollars per share) $ 2.12      
Weighted-Average Remaining Contractual Term, Outstanding (in years) 6 years 5 months 27 days   6 years 8 months 12 days  
Weighted-Average Remaining Contractual Term, Vested and expected to vest (in years) 6 years 5 months 27 days      
Weighted-Average Remaining Contractual Term, Unvested (in years) 7 years 5 months 16 days      
Weighted-Average Remaining Contractual Term, Exercisable (in years)       6 years 5 months 23 days
Aggregate Intrinsic Value, Outstanding $ 14,458   $ 255,000  
Aggregate Intrinsic Value, Vested and expected to vest 0      
Aggregate Intrinsic Value, Unvested 0      
Aggregate Intrinsic Value, Exercisable $ 14,458