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Asset Retirement Obligations - Schedule of Changes in Asset Retirement Obligations (Details)
$ in Thousands
3 Months Ended
Mar. 31, 2019
USD ($)
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]  
December 31, 2018 $ 52,449
Liabilities incurred during period 405
Liabilities settled during period (72)
Accretion expense during period 718
Liabilities held for sale 827
March 31, 2019 $ 54,327