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Asset Retirement Obligations
 12 Months Ended
Dec. 31, 2016
Asset Retirement Obligation Disclosure [Abstract]  
Asset Retirement Obligations
Note 2. Asset Retirement Obligations

The following table summarizes the changes in our asset retirement obligations for the years ended December 31, 2016 and 2015:
 
 
Year Ended December 31,
In thousands
 
2016
 
2015
Beginning asset retirement obligations
 
$
145,696

 
$
128,095

Liabilities incurred and assumed during period
 
5,383

 
9,628

Revisions in estimated retirement obligations
 
6,238

 
5,238

Liabilities settled and sold during period
 
(19,878
)
 
(6,914
)
Accretion expense
 
11,681

 
9,649

Ending asset retirement obligations
 
149,120

 
145,696

Less: current asset retirement obligations (1)
 
(2,313
)
 
(6,777
)
Long-term asset retirement obligations
 
$
146,807

 
$
138,919



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

Liabilities assumed relate to minor acquisitions, with liabilities incurred generally relating to wells and facilities.

We have escrow accounts that are legally restricted for certain of our asset retirement obligations.  The balances of these escrow accounts were $39.3 million and $38.2 million as of December 31, 2016 and 2015, respectively.  These balances are primarily invested in U.S. Treasury bonds, are recorded at amortized cost and are included in “Other assets” in our Consolidated Balance Sheets.  The carrying value of these investments approximates their estimated fair market value as of December 31, 2016 and 2015.