XML 56 R35.htm IDEA: XBRL DOCUMENT v3.3.1.900
Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2015
Asset Retirement Obligation Disclosure [Abstract]  
Asset Retirement Obligations Table
The following table provides a summary of changes in asset retirement obligations:
 
 
Year Ended December 31,
thousands
 
2015
 
2014
Carrying amount of asset retirement obligations at beginning of year
 
$
110,735

 
$
78,535

Liabilities incurred
 
9,121

 
13,982

Liabilities settled
 
(7,377
)
 
(4,195
)
Accretion expense
 
5,943

 
4,879

Revisions in estimated liabilities
 
2,105

 
17,534

Carrying amount of asset retirement obligations at end of year
 
$
120,527

 
$
110,735