Acquisitions and Divestitures (Details) $ in Thousands, shares in Millions	1 Months Ended	6 Months Ended
	Dec. 31, 2017 USD ($) a shares	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jan. 31, 2018 USD ($)	Dec. 15, 2017 USD ($)	Apr. 17, 2017 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Liabilities related to oil and gas properties sold		$ 28,214	$ 248
Interests In East Lake Verret Field
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net proceeds from sale of a majority of interests						$ 2,200
Saltwater Disposal Assets In East Texas
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net proceeds from sale of a majority of interests					$ 8,500
Gulf Of Mexico Properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Purchase commitment, remaining minimum amount committed				$ 3,800
Final purchase price adjustments		(2,800)
Purchase price adjustment cash payment		2,400
Purchase price adjustment, payable		(400)
Liabilities related to oil and gas properties sold		28,200
Refund receivable		$ 12,300		$ 12,700
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	$ 10,700
Common shares issued in connection with acquisition (in shares) | shares	2.0