Acquisitions, Divestitures, and Assets Held for Sale Assets Held for Sale (Details) $ in Thousands	3 Months Ended	9 Months Ended
	Mar. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Oct. 21, 2015 USD ($)	Dec. 31, 2014 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets Held-for-sale Reasonably Certain Period for Sale		1
Disposal Group, Including Discontinued Operation, Assets, Current		$ 29,173		$ 17,891
Asset Retirement Obligations Assets Held-for-sale Noncurrent		3,300
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down		$ 98,600
Mid Continent Divestiture 2015 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down	$ 30,000
Subsequent Event [Member] | Permian Divestiture 2015 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Purchase Price for Divestiture Package			$ 26,000