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Exploration and Production Activities (Unaudited) Results of operations (Details 4) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                      
Income (loss) from discontinued operations, net of tax $ 6,261 $ (202,626) $ (251,415) $ (324,605) $ 27,700 $ 38,482 $ 23,881 $ 25,112 $ (772,385) $ 115,175 $ 109,879
Discontinued operations, disposed of by sale                      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                      
Income (loss) from discontinued operations, net of tax                 $ (772,385) $ 111,998 $ 110,191