Commitment and contingencies variable interest entities (Details 4) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Dec. 01, 2014	Sep. 30, 2014
Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Percent of ownership	50.00%
Total project costs	$ 300,000
Portion of capital commitment	150,000
Partner portion of capital commitment	75,000
Excess capital commitments	300,000
Term loan for project debt financing	75,000
Line of credit facility, maximum borrowing capacity	75,000		$ 50,000
Dakota Prairie Refining, LLC [Member] | Cash and cash equivalents [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, assets	625	$ 21,376		$ 16,723
Dakota Prairie Refining, LLC [Member] | Accounts receivable [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, assets	14,648	2,759		150
Dakota Prairie Refining, LLC [Member] | Inventories [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, assets	12,354	5,311		0
Dakota Prairie Refining, LLC [Member] | Other current assets [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, assets	7,125	4,019		4,187
Dakota Prairie Refining, LLC [Member] | Total current assets [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, assets	34,752	33,465		21,060
Dakota Prairie Refining, LLC [Member] | Net property, plant and equipment [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, assets	428,383	398,984		314,551
Dakota Prairie Refining, LLC [Member] | Other [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, assets	5,052	3,400		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	5,052	3,400		0
Dakota Prairie Refining, LLC [Member] | Total assets [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, assets	468,187	435,849		335,611
Dakota Prairie Refining, LLC [Member] | Short-term borrowings [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, liabilities	29,500	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	4,125	3,000		3,000
Dakota Prairie Refining, LLC [Member] | Accounts payable [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, liabilities	21,686	55,089		36,541
Dakota Prairie Refining, LLC [Member] | Taxes payable [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, liabilities	1,630	648		323
Dakota Prairie Refining, LLC [Member] | Accrued compensation [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, liabilities	1,059	727		617
Dakota Prairie Refining, LLC [Member] | Other accrued liabilities [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, liabilities	1,217	899		633
Dakota Prairie Refining, LLC [Member] | Total current liabilities [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, liabilities	59,217	60,363		41,114
Dakota Prairie Refining, LLC [Member] | Long-term debt [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, liabilities	64,875	69,000		69,000
Dakota Prairie Refining, LLC [Member] | Total liabilities [Member]
Variable Interest Entities [Line Items]
Limited liability entity, consolidated, carrying amount, liabilities	124,092	$ 129,363		$ 110,114
Fuel contract [Member]
Variable Interest Entities [Line Items]
Variable interest entity, reporting entity involvement, maximum loss exposure, amount	33,900
WBI Holdings [Member] | Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Cumulative capital contributions, net of distributions	230,400
Noncontrolling interest [Member] | Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Cumulative capital contributions, net of distributions	$ 163,600
Percent of credit agreement guaranteed	50.00%
Centennial Energy Holdings, Inc [Member] | Dakota Prairie Refining, LLC [Member]
Variable Interest Entities [Line Items]
Percent of credit agreement guaranteed	50.00%