Assets Held for Sale, Divestitures and Acquisitions Assets Held for Sale and Divestitures (Details) - USD ($) $ in Thousands, shares in Millions			1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
		Aug. 12, 2016	Oct. 26, 2016	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest				$ (64,639)	$ (1,026)	$ (871,303)	$ (185,748)
Restricted Cash and Cash Equivalents, Noncurrent				49,000		49,000		$ 0
Proceeds from Sale of Oil and Gas Property and Equipment						201,829	335,103
Asset retirement obligation associated with oil and gas properties held for sale				46,290		46,290		241
Disposal Group, Including Discontinued Operation, Assets, Current				1,109,517		$ 1,109,517		641
Assets Held-for-sale Reasonably Certain Period for Sale						1 year
Business Exit Costs				2,900
Stock Issued During Period, Shares, New Issues		18.4
Impairment of Proved Oil and Gas Properties				8,049	55,990	$ 277,834	124,430	$ 468,700
Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	[1]			$ 20,309	(15,132)	(289,563)	55,445
Impairment of Proved Oil and Gas Properties					17,800	269,600	17,800
Permian Divestiture 2016 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal						(10,100)
Proceeds from Sale of Oil and Gas Property and Equipment						54,600
Rocky Mountain Divestiture 2016 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal						16,400
Proceeds from Sale of Oil and Gas Property and Equipment						$ 110,600
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, Gain (Loss) on Disposal							108,400
Proceeds from Sale of Oil and Gas Property and Equipment							310,200
Business Exit Costs					$ 1,000		$ 9,500
Subsequent Event [Member] | Raven/Bear Den [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from Sale of Oil and Gas Property and Equipment			$ 785,000

[1] Income (loss) before income taxes reflects oil, gas, and NGL production revenue less oil, gas, and NGL production expense, depletion, depreciation, amortization, and asset retirement obligation liability accretion, and related general and administrative expense and exploration overhead. Additionally, loss before income taxes for the nine months ended September 30, 2016, includes $269.6 million of proved property impairments, and income (loss) before income taxes for the three and nine months ended September 30, 2015, includes $17.8 million of proved property impairment