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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, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
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 $ 350 $ 478 1,022 $ 1,434 1,911
Asset retirement obligation, end of period 14,021   14,021   13,038
Asset Retirement Obligation [Abstract]          
 Current 131   131   131
Asset Retirement Obligation Held For Sale, Current 242   242   0
 Non-current 13,648   13,648   12,907
Asset retirement obligation, end of period $ 14,021   $ 14,021   $ 13,038