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Fixed Assets - ARO Rollforward (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Fixed Assets And Asset Retirement Obligations [Abstract]        
Gain on sale of assets $ 26,684 $ 0 $ 26,684 $ 0
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]        
ARO liability balance, December 31, 2016     213,726  
Accretion expense     5,581  
Change in estimate     729  
Divestitures     (7,649)  
Settlements     (12,553)  
Other     240  
ARO liability balance, June 30, 2017 $ 200,074   $ 200,074