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Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2015
Asset Retirement Obligation Disclosure [Abstract]  
Schedule Of Changes In Asset Retirement Obligation
 
2015
 
2014
 
2013
Asset retirement obligation at beginning of year
$
3,028

 
$
2,859

 
$
3,168

Liabilities incurred
12,539

 
—

 
—

Liabilities settled
(29
)
 
(41
)
 
(263
)
Accretion expense (income)
459

 
210

 
(46
)
Asset retirement obligation at end of year
$
15,997

 
$
3,028

 
$
2,859