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Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2015
Asset Retirement Obligation Disclosure [Abstract]  
Summary of change in asset retirement obligations
The following table presents a reconciliation of the Company’s asset retirement obligations:
 
December 31,
 
2015
 
2014
 
(in thousands)
 
 
 
 
Asset retirement obligations at beginning of year
$
121,760

 
$
94,830

Liabilities added from drilling
1,270

 
5,124

Settlements
(683
)
 
(5,260
)
Liabilities added from acquisitions
—

 
25,223

Liabilities associated with assets divested
—

 
(5,460
)
Current year accretion expense
6,897

 
5,670

Revision of estimates
8,319

 
1,633

Asset retirement obligations at end of year
$
137,563

 
$
121,760