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Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2013
Asset Retirement Obligation Disclosure [Abstract]  
Schedule of Changes to the Company's Before-tax Asset Retirement Obligation
The following table indicates the changes to the company’s before-tax asset retirement obligations in 2013, 2012 and 2011:
 
2013

 
 
2012

 
2011

Balance at January 1
$
13,271

 
 
$
12,767

 
$
12,488

Liabilities incurred
59

 
 
133

 
62

Liabilities settled
(907
)
 
 
(966
)
 
(1,316
)
Accretion expense
627

 
 
629

 
628

Revisions in estimated cash flows
1,248

 
 
708

 
905

Balance at December 31
$
14,298

 
 
$
13,271

 
$
12,767