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Asset Retirement Obligations - Schedule of Changes in Asset Retirement Obligations (Details)
$ in Thousands
3 Months Ended
Mar. 31, 2018
USD ($)
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]  
December 31, 2017 $ 48,799
Liabilities incurred during period 2,703
Liabilities settled during period (1)
Accretion expense during period 665
Liabilities held for sale 84
March 31, 2018 $ 52,250