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Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2017
Asset Retirement Obligation Disclosure [Abstract]  
Changes In Asset Retirement Obligations
The following table summarizes the changes in our asset retirement obligations for the years ended December 31, 2017 and 2016:
 
 
Year Ended December 31,
In thousands
 
2017
 
2016
Beginning asset retirement obligations
 
$
149,120

 
$
145,696

Liabilities incurred and assumed during period
 
2,698

 
5,383

Revisions in estimated retirement obligations
 
6,867

 
6,238

Liabilities settled and sold during period
 
(5,617
)
 
(19,878
)
Accretion expense
 
13,242

 
11,681

Ending asset retirement obligations
 
166,310

 
149,120

Less: current asset retirement obligations (1)
 
(554
)
 
(2,313
)
Long-term asset retirement obligations
 
$
165,756

 
$
146,807



(1)
Included in “Accounts payable and accrued liabilities” in our Consolidated Balance Sheets.