SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Summary of Valuation Input for Warrant and Derivative Liabilities (Details)
Jun. 30, 2019
year
month
$ / shares
May 17, 2019
year
$ / shares
May 01, 2019
year
$ / shares
Mar. 18, 2019
year
$ / shares
Mar. 08, 2019
month
$ / shares
Dec. 31, 2018
month
$ / shares
Jan. 29, 2018
Discount rate              
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Derivative liability, measurement input 0.291       0.293 0.136  
Expected stock price volatility              
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Derivative liability, measurement input 1.056       1.011 1.056  
Warrants and rights outstanding, measurement input             0.848
Expected stock price volatility | Short-term Warrants              
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Warrants and rights outstanding, measurement input 0.853     1.220      
Expected stock price volatility | Long-term Warrants              
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Warrants and rights outstanding, measurement input   0.834 0.841 0.852      
Risk-free interest rate              
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Derivative liability, measurement input 0.018       0.025 0.025  
Warrants and rights outstanding, measurement input             0.025
Risk-free interest rate | Short-term Warrants              
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Warrants and rights outstanding, measurement input 0.020     0.025      
Risk-free interest rate | Long-term Warrants              
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Warrants and rights outstanding, measurement input   0.022 0.022 0.022      
Expected Term              
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Derivative liability, measurement input | month 20       24 21  
Expected Term | Short-term Warrants              
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Warrants and rights outstanding, measurement input | year 1     1      
Expected Term | Long-term Warrants              
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Warrants and rights outstanding, measurement input | year       5      
Price of the underlying common stock              
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Derivative liability, measurement input 1.16       1.99 2.31  
Price of the underlying common stock | Short-term Warrants              
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Warrants and rights outstanding, measurement input 1.16     2.48      
Price of the underlying common stock | Long-term Warrants              
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Warrants and rights outstanding, measurement input 1.16 1.58 1.54 2.48      
Conversion price | Short-term Warrants              
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Warrants and rights outstanding, measurement input 4.00     4.00      
Conversion price | Long-term Warrants              
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Warrants and rights outstanding, measurement input   2.13   2.56      
Minimum | Expected stock price volatility | Long-term Warrants              
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Warrants and rights outstanding, measurement input 0.83            
Minimum | Risk-free interest rate | Long-term Warrants              
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Warrants and rights outstanding, measurement input 0.018            
Minimum | Expected Term | Long-term Warrants              
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Warrants and rights outstanding, measurement input | year 5 5 5        
Minimum | Conversion price | Long-term Warrants              
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Warrants and rights outstanding, measurement input 2.13   2.13        
Maximum | Expected stock price volatility | Long-term Warrants              
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Warrants and rights outstanding, measurement input 0.835            
Maximum | Risk-free interest rate | Long-term Warrants              
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Warrants and rights outstanding, measurement input 0.020            
Maximum | Expected Term | Long-term Warrants              
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Warrants and rights outstanding, measurement input | year 5.5   5.5        
Maximum | Conversion price | Long-term Warrants              
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Warrants and rights outstanding, measurement input 2.56   2.53