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Divestiture (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Jan. 21, 2016
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Disposal Group, Not Discontinued Operation, Disposal Disclosures [Abstract]          
Cash paid on settlement of contract       $ 11,000 $ 0
Loss on settlement of contract   $ 0 $ 0 90,184 $ 0
Disposed of by Means Other Than Sales | WTO Properties          
Disposal Group, Not Discontinued Operation, Disposal Disclosures [Abstract]          
Cash paid on settlement of contract $ 11,000        
Treating Agreement | WTO Properties          
Disposal Group, Not Discontinued Operation, Disposal Disclosures [Abstract]          
Reduction in asset retirement obligations       34,100  
Treating Agreement | Disposed of by Means Other Than Sales | WTO Properties          
Disposal Group, Not Discontinued Operation, Disposal Disclosures [Abstract]          
Contract agreement, term 30 years        
Cumulative shortfall accrued $ 111,900        
Loss on settlement of contract       $ 89,100