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Commitment and contingencies variable interest entities (Details 4) - USD ($) | Jun. 30, 2015 | Dec. 31, 2014 | Dec. 01, 2014 | Jun. 30, 2014
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Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Percent of ownership | 50.00% |  |  |
Total project costs | $ 300,000,000 |  |  |
Portion of capital commitment | 150,000,000 |  |  |
Partner portion of capital commitment | 75,000,000 |  |  |
Excess capital commitments | 300,000,000 |  |  |
Term loan for project debt financing | 75,000,000 |  |  |
Line of credit facility, maximum borrowing capacity |  |  | $ 50,000,000 |
Dakota Prairie Refining, LLC [Member] | Cash and cash equivalents [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Limited liability entity, consolidated, carrying amount, assets | 845,000 | $ 21,376,000 |  | $ 32,283,000
Dakota Prairie Refining, LLC [Member] | Accounts receivable [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Limited liability entity, consolidated, carrying amount, assets | 29,639,000 | 2,759,000 |  | 0
Dakota Prairie Refining, LLC [Member] | Inventories [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Limited liability entity, consolidated, carrying amount, assets | 24,166,000 | 5,311,000 |  | 0
Dakota Prairie Refining, LLC [Member] | Other current assets [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Limited liability entity, consolidated, carrying amount, assets | 7,887,000 | 4,019,000 |  | 2,136,000
Dakota Prairie Refining, LLC [Member] | Total current assets [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Limited liability entity, consolidated, carrying amount, assets | 62,537,000 | 33,465,000 |  | 34,419,000
Dakota Prairie Refining, LLC [Member] | Net property, plant and equipment [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Limited liability entity, consolidated, carrying amount, assets | 431,476,000 | 398,984,000 |  | 254,079,000
Dakota Prairie Refining, LLC [Member] | Other [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Limited liability entity, consolidated, carrying amount, assets | 5,729,000 | 3,400,000 |  | 0
Dakota Prairie Refining, LLC [Member] | Total deferred charges and other assets [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Limited liability entity, consolidated, carrying amount, assets | 5,729,000 | 3,400,000 |  | 0
Dakota Prairie Refining, LLC [Member] | Total assets [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Limited liability entity, consolidated, carrying amount, assets | 499,742,000 | 435,849,000 |  | 288,498,000
Dakota Prairie Refining, LLC [Member] | Short-term borrowings [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Limited liability entity, consolidated, carrying amount, liabilities | 26,000,000 | 0 |  | 0
Dakota Prairie Refining, LLC [Member] | Long-term debt due within one year [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Limited liability entity, consolidated, carrying amount, liabilities | 3,000,000 | 3,000,000 |  | 3,000,000
Dakota Prairie Refining, LLC [Member] | Accounts payable [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Limited liability entity, consolidated, carrying amount, liabilities | 38,339,000 | 55,089,000 |  | 28,150,000
Dakota Prairie Refining, LLC [Member] | Taxes payable [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Limited liability entity, consolidated, carrying amount, liabilities | 1,601,000 | 648,000 |  | 225,000
Dakota Prairie Refining, LLC [Member] | Accrued compensation [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Limited liability entity, consolidated, carrying amount, liabilities | 649,000 | 727,000 |  | 256,000
Dakota Prairie Refining, LLC [Member] | Other accrued liabilities [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Limited liability entity, consolidated, carrying amount, liabilities | 932,000 | 899,000 |  | 494,000
Dakota Prairie Refining, LLC [Member] | Total current liabilities [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Limited liability entity, consolidated, carrying amount, liabilities | 70,521,000 | 60,363,000 |  | 32,125,000
Dakota Prairie Refining, LLC [Member] | Long-term debt [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Limited liability entity, consolidated, carrying amount, liabilities | 66,000,000 | 69,000,000 |  | 69,000,000
Dakota Prairie Refining, LLC [Member] | Total liabilities [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Limited liability entity, consolidated, carrying amount, liabilities | 136,521,000 | $ 129,363,000 |  | $ 101,125,000
Fuel contract [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Variable interest entity, reporting entity involvement, maximum loss exposure, amount | 26,100,000 |  |  |
WBI Holdings [Member] | Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Cumulative capital contributions | 234,500,000 |  |  |
Percent of credit agreement guaranteed |  |  | 50.00% |
Noncontrolling interest [Member] | Dakota Prairie Refining, LLC [Member] |  |  |  |
Variable Interest Entities [Line Items] |  |  |  |
Cumulative capital contributions | $ 159,500,000 |  |  |
Percent of credit agreement guaranteed |  |  | 50.00% |

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