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Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2016
Asset Retirement Obligation Disclosure [Abstract]  
Schedule of changes in asset retirement obligations
The following table reflects the changes in ARO for the years ended December 31, 2016 and 2015:
 
 
2016
 
2015
 
(In thousands)
Beginning of year
$
48,728

 
$
45,697

Additional ARO from new properties
61

 
469

Sales or abandonments of properties
(17,206
)
 
(4,435
)
Accretion expense
4,364

 
3,945

Revisions of previous estimates
11,276

 
3,052

End of year
$
47,223

 
$
48,728