Quarterly report pursuant to Section 13 or 15(d)

4. Derivatives - Schedule of Derivatives Not Designated as Hedging Instruments (Details)

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4. Derivatives - Schedule of Derivatives Not Designated as Hedging Instruments (Details) - Commodity Contracts [Member] - Non Designated Derivative Instruments [Member] - USD ($)
$ in Thousands
Mar. 31, 2017
Dec. 31, 2016
Commodity contracts - Derivative assets $ 594 $ 978
Commodity contracts - Derivative liabilities $ 1,171 $ 4,115