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Summary of Significant Accounting Policies - Estimated Useful Life of Property, Plant and Equipment (Detail) | 12 Months Ended
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Dec. 31, 2017
Land and Improvements |
Property Plant And Equipment [Line Items] |
Property, plant and equipment, useful life | 10 years
Rail Spur |
Property Plant And Equipment [Line Items] |
Property, plant and equipment, useful life | 30 years
Deferred Mining Costs |
Property Plant And Equipment [Line Items] |
Property, plant and equipment, useful life | 3 years
Minimum | Plant and Building |
Property Plant And Equipment [Line Items] |
Property, plant and equipment, useful life | 5 years
Minimum | Real Estate Properties |
Property Plant And Equipment [Line Items] |
Property, plant and equipment, useful life | 10 years
Minimum | Vehicles |
Property Plant And Equipment [Line Items] |
Property, plant and equipment, useful life | 3 years
Minimum | Machinery, Equipment and Tooling |
Property Plant And Equipment [Line Items] |
Property, plant and equipment, useful life | 3 years
Minimum | Furniture and Fixtures |
Property Plant And Equipment [Line Items] |
Property, plant and equipment, useful life | 3 years
Maximum | Plant and Building |
Property Plant And Equipment [Line Items] |
Property, plant and equipment, useful life | 15 years
Maximum | Real Estate Properties |
Property Plant And Equipment [Line Items] |
Property, plant and equipment, useful life | 40 years
Maximum | Vehicles |
Property Plant And Equipment [Line Items] |
Property, plant and equipment, useful life | 5 years
Maximum | Machinery, Equipment and Tooling |
Property Plant And Equipment [Line Items] |
Property, plant and equipment, useful life | 15 years
Maximum | Furniture and Fixtures |
Property Plant And Equipment [Line Items] |
Property, plant and equipment, useful life | 10 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. + References No definition available. + Details
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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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- Details
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- Details
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