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Derivative Instruments (Details 1) - Energy contracts and options [Member] - USD ($) $ in Thousands | Sep. 30, 2018 | Dec. 31, 2017
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Other current assets [Member] |  |
Schedule of fair value of outstanding derivative instruments recorded as assets and liability |  |
Asset Derivatives not designated or not qualifying as hedging instruments | $ 2,485 | $ 4,358
Other current liabilities [Member] |  |
Schedule of fair value of outstanding derivative instruments recorded as assets and liability |  |
Liability Derivatives not designated or not qualifying as hedging instruments | $ 701 | $ 1,228

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