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Summary of Significant Accounting Policies - Computation of Depreciation of Property and Equipment (Detail) | 12 Months Ended
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Dec. 31, 2018
Buildings and improvements | Minimum |
Property Plant And Equipment [Line Items] |
Property and equipment useful life | 10 years
Buildings and improvements | Maximum |
Property Plant And Equipment [Line Items] |
Property and equipment useful life | 40 years
Machinery and equipment | Minimum |
Property Plant And Equipment [Line Items] |
Property and equipment useful life | 3 years
Machinery and equipment | Maximum |
Property Plant And Equipment [Line Items] |
Property and equipment useful life | 20 years
Mine development costs |
Property Plant And Equipment [Line Items] |
Property and equipment useful life | Units-of-production

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- Definition Description of the methodology for computing depreciation for classes of depreciable assets. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 + Details
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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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