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ASSET RETIREMENT OBLIGATIONS (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Activity related to ARO liability    
Liability for asset retirement obligations at the beginning of the period $ 4,368 $ 32,375
Liabilities settled and divested (590) (33,796)
Additions 988 592
Acquisitions 2,465 3,109
Accretion expense 329 1,306
Revisions in estimated cash flows (646) 782
Liability for asset retirement obligations at the end of the period $ 6,914 $ 4,368