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ASSET RETIREMENT OBLIGATIONS AND RESTRICTED CASH - Schedule of Change in Asset Retirement Obligation (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2020
Sep. 30, 2019
Sep. 30, 2020
Sep. 30, 2019
Dec. 31, 2019
Sep. 30, 2020
Dec. 31, 2019
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]              
Asset retirement obligation, beginning of period     $ 18,972 $ 19,104 $ 19,104    
 Revision of estimate     0   (2,063)    
 Accretion of liabilities $ 478 $ 484 1,434 1,478 1,931    
Asset retirement obligation, end of period 20,406   20,406   18,972    
Asset Retirement Obligation [Abstract]              
 Current           $ 46 $ 46
 Non-current           20,360 18,926
Asset retirement obligation, end of period $ 20,406   $ 20,406 $ 19,104 $ 19,104 $ 20,406 $ 18,972