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Asset Retirement Obligation | 12 Months Ended
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Dec. 31, 2017
Asset Retirement Obligation Disclosure [Abstract] |
Asset Retirement Obligations | Note 8—Asset Retirement Obligations The table below summarizes the changes in our recorded asset retirement obligations (in thousands):
| Year Ended December 31,
| 2017 |  | 2016 |  | 2015
Beginning balance | $ | 9,042 |  |  | $ | 8,909 |  |  | $ | 2,580 |
Obligations acquired | — |  |  | — |  |  | 5,725 |
Accretion expense | 369 |  |  | 362 |  |  | 604 |
Liabilities settled during period | (308 | ) |  | (229 | ) |  | — |
Ending balance | $ | 9,103 |  |  | $ | 9,042 |  |  | $ | 8,909 |

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- Definition The entire disclosure for an asset retirement obligation and the associated long-lived asset. An asset retirement obligation is a legal obligation associated with the disposal or retirement from service 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -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 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7569-110849 + Details
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