Divestitures, Assets Held for Sale, and Acquisitions Divestitures and Assets Held for Sale (Details) - USD ($) $ in Thousands		3 Months Ended				9 Months Ended
		Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net divestiture proceeds						$ 778,365	$ 201,829
Net gain on divestiture activity		$ (1,895)			$ 22,388	(131,565)	3,413
Income (loss) before income taxes		(128,382)			(64,639)	(200,410)	(871,303)
Impairment of proved properties		0			8,049	3,806	277,834
Assets held for sale		7,144				7,144		$ 372,621
Other Divestitures 2016 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net divestiture proceeds					165,200
Net gain on divestiture activity					22,400
Accrued costs and payments to Net Profits Plan participants					23,600		23,600
Assets held for sale, Loss (Gain) on Write-down							(6,300)
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | Non-Operated Eagle Ford Divestiture 2017 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net divestiture proceeds						747,400
Net gain on divestiture activity						396,800
Income (loss) before income taxes	[1]	0			$ 22,116	24,324	(251,451)
Impairment of proved properties							$ 269,600
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | Other Divestitures 2017 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net divestiture proceeds		$ 31,000
Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Divide County Disposal Group [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment of proved properties						$ 526,500
Assets held for sale, Loss (Gain) on Write-down			$ 166,900	$ 359,600

[1] Income (loss) before income taxes reflects oil, gas, and NGL production revenue, less oil, gas, and NGL production expense, and depletion, depreciation, amortization, and asset retirement obligation liability accretion. Additionally, income (loss) before income taxes included impairment of proved properties expense of approximately $269.6 million for the nine months ended September 30, 2016.