Significant Accounting Policies - Percentage of Revenue by Major Customers (Details) - Sales Revenue Net - Customer Concentration Risk |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
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| Shell Trading (US) Co. | |||
| Entity Wide Revenue Major Customer [Line Items] | |||
| Percentage of receipts | 46.00% | 43.00% | 50.00% |
| Vitol Inc. | |||
| Entity Wide Revenue Major Customer [Line Items] | |||
| Percentage of receipts | 15.00% | 20.00% | |
| J. P. Morgan | |||
| Entity Wide Revenue Major Customer [Line Items] | |||
| Percentage of receipts | 14.00% | ||
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- Definition For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition 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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