Asset Retirement Obligations (Summary of Changes In Asset Retirement Obligations) (Details) - USD ($) $ in Thousands |
12 Months Ended | ||
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Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
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| Asset Retirement Obligations [Abstract] | |||
| Balance at January 1 | $ 18,612 | $ 16,166 | $ 14,846 |
| Accretion | 951 | 903 | 778 |
| Additions | 1,085 | ||
| Acquisitions and dispositions | (103) | 1,544 | |
| Revisions | 703 | (1) | (543) |
| Balance at December 31 | $ 20,163 | $ 18,612 | $ 16,166 |
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- Definition Asset Retirement Obligation, Acquisitions And Dispositions 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. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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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. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- References No definition available.
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- Definition Amount of asset retirement obligations incurred during the period. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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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. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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