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Asset retirement obligations (“ARO”) | 12 Months Ended
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Dec. 31, 2014
Asset Retirement Obligation Disclosure [Abstract] |
Asset retirement obligations (“ARO”) | Asset retirement obligations ("ARO") Our asset retirement obligations consist primarily of costs associated with the disposal of spent pot liner used in the reduction cells of our domestic facilities. The reconciliation of the changes in the asset retirement obligations is presented below:
| Year ended December 31,
| 2014 | 2013
Beginning balance, ARO liability | $ | 27,113 |  | $ | 16,124 |
Additional ARO liability incurred | 2,548 |  | 1,730 |
ARO liabilities settled | (4,731 | ) | (2,580 | )
Accretion expense | 1,517 |  | 1,733 |
Additional ARO liability from Sebree acquisition | — |  | 10,106 |
Additional ARO liability from Mt. Holly acquisition | 10,503 |  | — |
Ending balance, ARO liability | $ | 36,950 |  | $ | 27,113 |
Certain conditional AROs related to the disposal costs of fixed assets at our primary aluminum facilities have not been recorded because they have an indeterminate settlement date. These conditional AROs will be initially recognized in the period in which sufficient information exists to estimate their fair value.

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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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