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Asset Retirement Obligation
 12 Months Ended
Dec. 31, 2016
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,
 
2016
 
2015
 
2014
Beginning balance
$
8,909

 
$
2,580

 
$
3,172

Obligations acquired
—

 
5,725

 
—

Accretion expense
362

 
604

 
239

Revision in estimate
—

 
—

 
(831
)
Liabilities settled during period
(229
)
 
—

 
—

Ending balance
$
9,042

 
$
8,909

 
$
2,580


The revision in estimate during the year ended December 31, 2014 resulted from a revised valuation of the retirement obligation related to the removal of the underground tanks at our retail locations.