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Acquisitions - Divestitures (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Proceeds from sale of property $ 333,229 $ 5,774 $ 12,333
Impairment 384,228 $ 6,887 $ 4,684
Proved oil and gas properties      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]      
Impairment $ 3,600