v3.19.1
ASSET RETIREMENT OBLIGATION (Tables)
12 Months Ended
Dec. 31, 2018
Asset Retirement Obligation Disclosure [Abstract]  
Schedule of changes to asset retirement obligations
Following is a table of the changes to our asset retirement obligations for the following periods (in thousands):
 
 
Year Ended December 31,
 
 
2018
 
2017
 
2016
Asset retirement obligation, at beginning of period
 
$
21,476

 
$
19,976

 
$
22,951

Liabilities settled
 
(19
)
 

 
(3
)
Liabilities incurred
 

 
29

 

Changes in estimated obligations
 

 
(87
)
 
(4,740
)
Accretion of discount
 
1,668

 
1,558

 
1,768

Total asset retirement obligation, at end of period
 
$
23,125

 
$
21,476

 
$
19,976