Financial Instruments - Notional amounts (Details) - Not Designated as Hedging Instrument [Member] - Commodity Contract [Member] - bbl bbl in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Short [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	2,704	3,386	10,467	9,980
Long [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	2,701	2,820	9,892	9,772

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.

No definition available.

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