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Derivatives - Schedule of Pre-Tax Gain (Loss) Recognized in the Statement of Operations (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Commodity derivatives | Cost of revenues      
Derivative Instruments, Gain (Loss) [Line Items]      
Cost of revenues $ (4,517) $ (1,338) $ 14,367
J. Aron repurchase obligation derivative | Cost of revenues      
Derivative Instruments, Gain (Loss) [Line Items]      
Cost of revenues 436 (29,810) 12,654
Interest rate derivatives | Interest Expense      
Derivative Instruments, Gain (Loss) [Line Items]      
Cost of revenues $ 489 $ 2,729 $ 0