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Asset Retirement Obligations - Schedule of ARO (Details)
$ in Thousands
6 Months Ended
Jun. 30, 2018
USD ($)
Asset Retirement Obligation  
Balance at beginning of period $ 48,553
Liabilities incurred 2,322
Liabilities settled (789)
Liabilities divested (3,782)
Accretion expense 1,223
Balance at end of period $ 47,527