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Property, Plant and Equipment, net (Tables)
 3 Months Ended
Mar. 31, 2018
Property, Plant and Equipment [Abstract]  
Schedule of net property, plant and equipment
Depreciation is calculated using the straight-line method over the estimated useful lives of the property, plant and equipment, which are:
 
 
Years
Land improvements
10
Plant and buildings
5-15
Real estate properties
10-40
Railroad and sidings
30
Vehicles
3-5
Machinery, equipment and tooling
3-15
Furniture and fixtures
3-10
Deferred mining costs
3
Net property, plant and equipment consisted of:
 
 
March 31, 2018
 
December 31, 2017
Machinery, equipment and tooling
$
10,529

 
$
8,242

Vehicles
1,544

 
1,546

Furniture and fixtures
730

 
720

Plant and building
83,057

 
81,561

Real estate properties
4,432

 
4,432

Railroad and sidings
25,286

 
10,254

Land improvements
23,156

 
16,378

Asset retirement obligation
8,657

 
8,408

Mineral properties
9,879

 
9,878

Deferred mining costs
657

 
657

Construction in progress
71,639

 
56,493

 
239,566

 
198,569

Less: accumulated depreciation and depletion
29,529

 
26,367

Total property, plant and equipment, net
$
210,037

 
$
172,202