Financial Instruments - Effects of Derivative Instruments on Statements of Income (Details) - Cost of Goods Sold [Member] - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Commodity Contracts [Member] \| Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain on the derivatives in designated and qualifying fair value hedges	$ 0	$ 0	$ 391	$ 0
Commodity Contracts [Member] \| Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on commodity contracts (nonqualifying)	2,301	672	8,427	(423)
Inventories [Member] \| Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain on the derivatives in designated and qualifying fair value hedges	$ 0	$ 0	$ (385)	$ 0

Amount of the increase (decrease) in fair value of the hedged item in a fair value hedge recognized in the income statement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 50
-Paragraph 1
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=109977999&loc=d3e76258-113986

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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

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4CC
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL109998890-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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