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Asset Retirement Obligations (Tables) | 12 Months Ended
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Dec. 31, 2017
Asset Retirement Obligation [Abstract] |
Reconciliation of the company's asset retirement obligation | A reconciliation of the Company's liability, which is included in other accrued liabilities and deferred credits and other liabilities - other on the Consolidated Balance Sheets, for the years ended December 31 was as follows:
| 2017 |  | 2016 |
| (In thousands)
Balance at beginning of year | $ | 314,970 |  | $ | 242,224 |
Liabilities incurred | 15,110 |  | 15,114 |
Liabilities settled | (4,981 | ) | (4,338 | )
Accretion expense* | 16,839 |  | 13,918 |
Revisions in estimates | 31 |  | 48,052 |
Balance at end of year | $ | 341,969 |  | $ | 314,970 |
* | Includes $15.6 million and $12.7 million in 2017 and 2016, respectively, related to regulatory assets.

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- Definition Tabular disclosure of the changes in carrying amount of a liability for asset retirement obligations, for changes such as new obligations, changes in estimates of existing obligations, spending on existing obligations, property dispositions, and foreign currency translation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13201-110859 + Details
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