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Asset Retirement Obligations - Schedule of ARO (Details)
$ in Thousands
6 Months Ended
Jun. 30, 2016
USD ($)
Asset Retirement Obligation  
Balance at beginning of period $ 145,606
Liabilities incurred 2,389
Liabilities settled (135)
Liabilities divested (16,353)
Accretion expense 3,559
Balance at end of period $ 135,066