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Derivatives - Open Commodity Derivative Contracts - Crude Oil (Details) - Crude Oil - Exchange Traded bbl in Thousands | 3 Months Ended
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Mar. 31, 2018 bbl
Derivative [Line Items] |  |
Percentage of derivative contracts expiring in the period | 94.70% |
Derivative contract expiration date | Jun. 30, 2017 |
Long |  |
Derivative [Line Items] |  |
Notional contracts (in thousands of Total Barrels) | 16,664 | [1]
Short |  |
Derivative [Line Items] |  |
Notional contracts (in thousands of Total Barrels) | 22,145 | [1]
[1] | of the exchange-traded contracts expire in the second quarter of 2018.

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- Definition Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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