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Financial Instruments (Narrative) (Details) BRL in Thousands, $ in Thousands, lb in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 USD ($) lb | Dec. 31, 2016 USD ($) lb | Dec. 31, 2017 BRL
Derivative [Line Items] |  |  |
Weight of aluminum that hedged future purchase of aluminum to meet fixed-price forward sales contract obligations, lbs | lb | 8.0 | 9.6 |
Amounts of unrealized after-tax gains on derivative instruments | $ 400 |  |
Aluminum Futures Contracts |  |  |
Derivative [Line Items] |  |  |
Notional amount | 8,200 | $ 8,000 |
Cost of Sales [Member] | Foreign Currency Forwards And Options [Member] |  |  |
Derivative [Line Items] |  |  |
Notional amount | $ 15,000 |  | BRL 48,800

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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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- Definition The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=35736893&loc=d3e80748-113994 + Details
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