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Short-term borrowings (Details 2) - Revolving credit facility [Member] - Short-term debt [Member] - Dakota Prairie Refining, LLC [Member] - USD ($) $ in Millions	Dec. 31, 2015	Sep. 30, 2015	Dec. 01, 2014
Short-term debt [Line Items]
Facility limit, maximum borrowing capacity	$ 75.0	$ 75.0	$ 50.0
Ratio of total debt to total capitalization as specified in debt convenants.	65.00%
Ratio of total funded debt to total capitalization as specified in debt covenants	65.00%

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- Definition

Ratio of total debt to total capitalization as specified in debt convenants.

+ References

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- Definition

Ratio of total funded debt to total capitalization as specified in debt covenants.

+ References

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X

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

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