Financial Instruments - Notional amounts (Details) - Not Designated as Hedging Instrument [Member] - Commodity Contract [Member] - bbl bbl in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Short [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	4,139	4,312
Long [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	3,375	4,131

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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