Commodity Derivatives (Details 2) - Commodity derivative contracts [Member] - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Settlement gains (losses)	$ 225	$ (674)	$ (231)	$ (1,060)
Unrealized gains (losses)	8,455	(5,348)	(396)	(5,587)
Total settlement and unrealized gains (losses), net	$ 8,680	$ (6,022)	$ (627)	$ (6,647)

Amount of gain (loss) from the increase (decrease) in fair value of derivative and nonderivative instruments designated as fair value hedging instruments recognized in the income statement.

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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

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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.

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The difference between the book value and the sale price of options, swaps, futures, forward contracts, and other derivative instruments. This element refers to the gain (loss) included in earnings.

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