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Asset Retirement Obligations | 9 Months Ended
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Sep. 30, 2017
Asset Retirement Obligation Disclosure [Abstract] |
Asset Retirement Obligations | Asset Retirement Obligations In the third quarter of 2017, an updated decommissioning study was completed for the Navajo Generating Station, which resulted in an increase to the asset retirement obligation ("ARO") in the amount of $22 million. The following schedule shows the change in our asset retirement obligations for the nine months ended September 30, 2017 (dollars in thousands):
Asset retirement obligations at January 1, 2017 | $ | 624,475 |
Changes attributable to: |  |
Accretion expense | 24,170 |
Estimated cash flow revisions | 22,211 |
Asset retirement obligations at September 30, 2017 | $ | 670,856 |
In accordance with regulatory accounting, APS accrues removal costs for its regulated utility assets, even if there is no legal obligation for removal. See detail of regulatory liabilities in Note 3.

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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 -URI http://asc.fasb.org/subtopic&trid=2175671 + Details
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