Acquisitions and Divestitures (Details) $ in Thousands, shares in Millions, Mcfe in Billions			1 Months Ended				12 Months Ended
	Dec. 20, 2017 USD ($) a	Jun. 04, 2015 USD ($)	Jan. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) Mcfe	Dec. 15, 2017 USD ($)	Apr. 17, 2017 USD ($)	Oct. 31, 2016 USD ($)	Apr. 20, 2016 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Other receivable				$ 7,750	$ 0		$ 7,750	$ 0
Gain on sale of assets							0	0	$ 21,937
Sale of oil and gas properties							10,707	25,482	$ 271,769
Decrease in asset retirement obligation liabilities related to divestiture of oil and gas properties							248	3,419
Deposit for surety bonds				8,300	0		8,300	0
Woodford And Mississippian Lime
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration received from sale		$ 280,000
Cash received from sale		257,700
Other receivable		$ 13,900
Proved reserves | Mcfe									227.2
Estimated proved reserves attributable to Sold Assets (percent of total)									57.00%
Sale of oil and gas properties, significant alteration threshold percent									25.00%
Gain on sale of assets								23,200
Sale of oil and gas properties							274,100
Woodford Shale Assets (East Hoss Assets)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration received from sale													$ 18,000
Oklahoma Assets
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration received from sale												$ 700
Sale of oil and gas properties								17,600
Decrease in asset retirement obligation liabilities related to divestiture of oil and gas properties								$ 3,300
Interests in East Lake Verret Field
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration received from sale											$ 2,200
Saltwater Disposal Assets in East Texas
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration received from sale										$ 8,500
Gulf of Mexico Properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash collateral, refund receivable				10,700			10,700
Deposit for surety bonds				$ 8,300			$ 8,300
East Texas
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale of oil and gas properties						$ 7,000
Payments to repurchase certain non-producing assets					$ 5,000
Austin Chalk Acreage
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Acres acquired | a	24,600
Purchase price	$ 9,300
Common shares issued in connection with acquisition | shares				2.0
Subsequent Event | Gulf of Mexico Properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Purchase commitment			$ 3,800
Pro Forma | Subsequent Event | Gulf of Mexico Properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Decrease in asset retirement obligation liabilities related to divestiture of oil and gas properties			$ 28,400