Asset Retirement Obligations - Changes in Asset Retirement Obligation Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Asset Retirement Obligation
Balance	$ 6,547	$ 7,408
Accretion	552	542	$ 562
Amounts paid	(177)	(154)
Additions	32	55
Reductions	(803)	(1,304)
Reclassifications	0	0
Balance	6,151	6,547	7,408
Total estimated liability	7,600
Short-Term Portion
Asset Retirement Obligation
Balance	34	234
Accretion	39	(91)
Amounts paid	(177)	(154)
Additions	0	0
Reductions	14	(185)
Reclassifications	180	230
Balance	90	34	234
Long-Term Portion
Asset Retirement Obligation
Balance	6,513	7,174
Accretion	513	633
Amounts paid	0	0
Additions	32	55
Reductions	(817)	(1,119)
Reclassifications	(180)	(230)
Balance	$ 6,061	$ 6,513	$ 7,174

Asset Retirement Obligation, Additions

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- Definition

Asset Retirement Obligation, Estimated Liability, Removal Costs and Timing Refinements

+ References

No definition available.

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- Definition

Asset Retirement Obligation, Other Period Increase (Decrease)

+ References

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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- 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://fasb.org/us-gaap/role/ref/legacyRef
-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://fasb.org/us-gaap/role/ref/legacyRef
-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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- 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.

+ References

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- Definition

Amount of increase (decrease) in the asset retirement obligation from changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 35
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6392603&loc=d3e7123-110846

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)(4)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

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