Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

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

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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

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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.

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- Definition

Nominal mass used to calculate payments on a derivative instrument.

+ References

No definition available.

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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