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Significant Accounting Policies (Schedule of Estimated Useful LIves of Property, Plant and Equipment) (Details)
 12 Months Ended
Dec. 31, 2017
Land development, roads and structures [Member]  
Property, Plant and Equipment [Line Items]  
Estimated Useful Life Depreciation in Years 15–30
Facilities, machinery and equipment [Member]  
Property, Plant and Equipment [Line Items]  
Estimated Useful Life Depreciation in Years 8–25 [1]
Dams and ponds [Member]  
Property, Plant and Equipment [Line Items]  
Estimated Useful Life Depreciation in Years 20–40 [2]
Heavy mechanical equipment, train cars and tanks [Member]  
Property, Plant and Equipment [Line Items]  
Estimated Useful Life Depreciation in Years 5-15
Office furniture and equipment, motor vehicles, computer equipment and other [Member]  
Property, Plant and Equipment [Line Items]  
Estimated Useful Life Depreciation in Years 3–10
[1] Mainly 25 years.
[2] Mainly 40 years.