Asset Retirement Obligation (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Asset Retirement Obligation
Asset retirement obligation, beginning balance			$ 6,074	$ 13,579	$ 13,579
Liabilities added from escalating working interests			288		198
Sales			(347)		(8,416)
Settlements					(60)
Accretion expense	$ 123	$ 240	249	$ 498	773
Asset retirement obligation, ending balance	6,264		6,264		6,074
Legally restricted assets	$ 0		$ 0		$ 0

Asset Retirement Obligation, Liabilities Incurred, Acquisitions

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- Definition

Asset Retirement Obligations Sold

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No definition available.

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- Definition

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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+ Details

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- Definition

Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6392676&loc=d3e7480-110848

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No definition available.

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- Definition

Carrying amount of an asset that is legally restricted for purposes of settling an asset retirement obligation.

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- Definition

Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset.

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