Significant Accounting Policies - Schedule of Economic Lives of Assets (Details)	12 Months Ended
	Dec. 31, 2017
Railroad and equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	15 years
Railroad and equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	30 years
Furniture and fixtures | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	5 years
Furniture and fixtures | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	10 years
Machinery and equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	3 years
Machinery and equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	10 years
Office equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	5 years
Office equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	10 years
Autos and trucks
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	5 years
Real Estate | Land improvements | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	15 years
Real Estate | Land improvements | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	20 years
Real Estate | Buildings | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	20 years
Real Estate | Buildings | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	40 years
Real Estate | Building improvements | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	5 years
Real Estate | Building improvements | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	25 years