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Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2017
Asset Retirement Obligation [Abstract]  
Schedule of Asset Retirement Obligations [Table Text Block]
Changes in the carrying amounts of the Company’s AROs for the years ended December 31, 2017 and 2016 are shown below:
(In thousands)
2017
2016
Balance at beginning of year
$
11,529

$
11,334

Liabilities settled
(577
)
(975
)
Liabilities incurred
412

491

Accretion expense
215

188

Revision of estimate
588

491

Balance at end of year
$
12,167

$
11,529