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Summary of Significant Accounting Policies - Estimated Useful Life of Property, Plant and Equipment (Detail)	3 Months Ended
	Mar. 31, 2018
Land improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	10 years
Plant and buildings | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years
Plant and buildings | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	15 years
Real estate properties | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	10 years
Real estate properties | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	40 years
Railroad and sidings
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	30 years
Vehicles | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	3 years
Vehicles | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years
Machinery, equipment and tooling | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	3 years
Machinery, equipment and tooling | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	15 years
Furniture and fixtures | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	3 years
Furniture and fixtures | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	10 years
Deferred mining costs
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	3 years

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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- Definition

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

+ References

No definition available.

+ Details

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