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Debt - Wyoming Refining Credit Facilities (Details) - USD ($)
12 Months Ended
Dec. 21, 2017
Apr. 30, 2015
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Debt Instrument [Line Items]          
Cost associated with termination of debt     $ 8,633,000 $ 0 $ 19,669,000
Revolving Credit Facility | Wyoming Refining Senior Secured Revolver          
Debt Instrument [Line Items]          
Line credit maximum borrowing amount   $ 30,000,000      
Cost associated with termination of debt $ 100,000        
Term Loan | Wyoming Refining Senior Secured Term Loan          
Debt Instrument [Line Items]          
Periodic payment, principal amount   $ 2,300,000      
Term Loan | Wyoming Refining Company | Wyoming Refining Senior Secured Term Loan | London Interbank Offered Rate (LIBOR)          
Debt Instrument [Line Items]          
Basis spread on variable rate   3.00%