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Fair value of the assets less the liabilities of a derivative or group of derivatives.

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Nominal energy measure used to calculate payments on a derivative instrument.

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Nominal mass used to calculate payments on a derivative instrument.

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The percentage of expected requirements covered by the aggregate notional amount of derivative contracts expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract as a percentage of expected need.

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Fair value as of the balance sheet date of all foreign currency derivatives designated as cash flow hedging instruments.

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Net fair value of all derivative instruments not designated as a hedging instrument.

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Fair value as of the balance sheet date of all price risk derivatives designated as cash flow hedging instruments.

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Amount after tax of reclassification adjustments of other comprehensive income (loss).

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Financial Instruments and Derivatives - Additional Information (Details) $ in Thousands, MMBTU in Millions	3 Months Ended
	Mar. 31, 2019 USD ($) MMBTU T	Apr. 01, 2018 USD ($)	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jan. 01, 2018 USD ($)
Derivative [Line Items]
Impact of new accounting pronouncements			$ (6,771)		$ 1,721
Fair value of commodity cash flow hedges, gain (loss)	$ (914)			$ (1,571)
Commodity gain (loss) expected to be reclassified to the income statement during the next 12 months	(918)
Fair value of foreign currency cash flow hedges, gain (loss)	155			(1,624)
Foreign currency gain (loss) expected to be reclassified to the income statement during the next 12 months	155
Total fair value of other derivatives not designated as hedging instruments	$ (164)			166
Natural Gas Swaps
Derivative [Line Items]
Approximate amount of commodity covered by swap contracts outstanding (in MMBTUs) \| MMBTU	6.0
Anticipated usage percentage covered by a swap contract for the current fiscal year	74.00%
Anticipated usage percentage covered by a swap contract for the second succeeding fiscal year	42.00%
Aluminum Swaps
Derivative [Line Items]
Anticipated usage percentage covered by a swap contract for the current fiscal year	51.00%
Approximate amount of commodity covered by swap contracts outstanding (in tons) \| T	3,062
Foreign Exchange Forward For Construction In Progress
Derivative [Line Items]
Net position of contracts	$ (57)			$ (88)
Retained Earnings
Derivative [Line Items]
Impact of new accounting pronouncements			$ (6,771)		1,897
Accumulated Other Comprehensive Loss
Derivative [Line Items]
Impact of new accounting pronouncements					$ (176)
Accumulated Other Comprehensive Loss \| Fixed Assets
Derivative [Line Items]
Amounts reclassified from accumulated other comprehensive loss	$ (45)	$ (45)