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Derivative Instruments - Balance Sheet Location (Details) - USD ($) $ in Thousands | Jun. 30, 2018 | Dec. 31, 2017
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Foreign currency derivatives | Not Designated as Hedging Instrument | Prepaid and other current assets |  |
Derivatives, Fair Value |  |
Derivative asset fair value | $ 23 | $ 9
Foreign currency derivatives | Not Designated as Hedging Instrument | Other current liabilities |  |
Derivatives, Fair Value |  |
Derivative liability fair value | 34 | 90
Cash Flow Hedging | Commodity derivative contracts | Designated as Hedging Instrument |  |
Derivatives, Fair Value |  |
Derivative asset fair value | 28,738 | 5,326
Derivative liability fair value | 58 | 581
Cash Flow Hedging | Commodity derivative contracts | Designated as Hedging Instrument | Prepaid and other current assets |  |
Derivatives, Fair Value |  |
Derivative asset fair value | 15,643 | 2,518
Cash Flow Hedging | Commodity derivative contracts | Designated as Hedging Instrument | Other accrued liabilities |  |
Derivatives, Fair Value |  |
Derivative liability fair value | 0 | 0
Cash Flow Hedging | Commodity derivative contracts | Designated as Hedging Instrument | Other long-term assets |  |
Derivatives, Fair Value |  |
Derivative asset fair value | 13,095 | 2,808
Cash Flow Hedging | Commodity derivative contracts | Designated as Hedging Instrument | Other long-term obligations |  |
Derivatives, Fair Value |  |
Derivative liability fair value | $ 58 | $ 581

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