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ASSET RETIREMENT OBLIGATIONS AND RESTRICTED CASH - Schedule of Change in Asset Retirement Obligation (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Dec. 31, 2020
Mar. 31, 2021
Dec. 31, 2020
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]          
Asset retirement obligation, beginning of period $ 13,038 $ 18,972 $ 18,972    
 Revision of estimate (39)   (7,845)    
 Accretion of liabilities 321 478 1,911    
Asset retirement obligation, end of period 13,320   13,038    
Asset Retirement Obligation [Abstract]          
 Current       $ 131 $ 131
 Non-current       13,189 12,907
Asset retirement obligation, end of period $ 13,320 $ 18,972 $ 18,972 $ 13,320 $ 13,038