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Asset Retirement Obligations (Tables)
12 Months Ended
Dec. 31, 2019
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 2019, 2018 and 2017:
 
2019

 
 
2018

 
2017

Balance at January 1
$
14,050

 
 
$
14,214

 
$
14,243

Liabilities incurred
32

 
 
96

 
684

Liabilities settled
(1,694
)
 
 
(830
)
 
(1,721
)
Accretion expense
628

 
 
654

 
668

Revisions in estimated cash flows
(184
)
 
 
(84
)
 
340

Balance at December 31
$
12,832

 
 
$
14,050

 
$
14,214