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Asset Retirement Obligation
 6 Months Ended
Jun. 30, 2017
Asset Retirement Obligation Disclosure [Abstract]  
Asset Retirement Obligation
Asset Retirement Obligation

The following table describes the changes to the Company’s asset retirement obligation liability (in thousands):
 
Six Months Ended June 30,
 
2017
 
2016
Asset retirement obligation, beginning of period
$
36,610

 
$
42,556

Liabilities incurred
574

 
—

Liabilities settled
(1,357
)
 
(2,574
)
Accretion expense
1,100

 
1,226

Revisions in estimates
(161
)
 
291

Divestiture of oil and gas properties
(248
)
 
(17
)
Asset retirement obligation, end of period
36,518

 
41,482

Less: current portion of asset retirement obligation
(2,759
)
 
(1,496
)
Long-term asset retirement obligation
$
33,759

 
$
39,986