Fair Value Measurements (Narrative) (Details) $ in Thousands, lb in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2019 USD ($) derivative_instrument lb $ / lb	Dec. 31, 2018 USD ($) derivative_instrument lb $ / lb	Mar. 31, 2018 USD ($)
Fair Value Disclosures [Abstract]
Number of years long-term sales growth forecasted over	6 years
Average long-term sales growth forecast, over next 4 years, percent per year	13.00%
Derivative, number of instruments held \| derivative_instrument	6	5
Underlying, derivative mass \| $ / lb	0.37	0.39
Derivative, nonmonetary notional amount, mass \| lb	52.6	34.4
Derivative instruments	$ 80		$ 0
Derivative liability	$ 1,125	$ 1,108	1,100
Derivative liability, current		900
Derivative liability, noncurrent		$ 200	$ 100

Long-term sales growth forecast, percent.

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Period long-term sales growth forecasted over.

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Unrealized Gain on Derivative Instruments

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled within one year or normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled after one year or the normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Nominal mass used to calculate payments on a derivative instrument.

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The number of derivative instruments of a particular group held by the entity.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 815
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-Section 50
-Paragraph 1A
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-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5580258-113959

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Specified interest rate, security price, commodity price, foreign exchange rate, index of prices or rates for a derivative contract measured in mass but not the derivative contract itself.

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