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Mineral Leaseholds, Net (Tables)
 3 Months Ended
Mar. 31, 2017
Mineral Leaseholds, Net [Abstract]  
Summary of Mineral Leaseholds, Net of Accumulated Depletion
Mineral leaseholds, net of accumulated depletion, consisted of the following:

  
March 31,
2017
  
December 31,
2016
 
Mineral leaseholds
 
$
2,005
  
$
1,996
 
Less accumulated depletion
  
(399
)
  
(389
)
Mineral leaseholds, net
 
$
1,606
  
$
1,607