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Derivative Financial Instruments - Schedule of Location and Fair Value Amounts of All Derivative Instruments (Details) - Derivatives Not Designated as Hedging Contracts - Commodity Contracts - USD ($)
$ in Thousands
Jun. 30, 2019
Dec. 31, 2018
Derivative asset - current    
Derivative Asset [Abstract]    
Gross Recognized Assets $ 17,346 $ 48,662
Gross Amounts Offset, Assets (8,768) (4,774)
Total financial assets 8,578 43,888
Derivative liability - current    
Derivative Liability [Abstract]    
Gross Recognized Liabilities 8,944 5,302
Gross Amounts Offset, Liabilities (8,768) (4,774)
Total financial liabilities 176 528
Derivative asset - noncurrent    
Derivative Asset [Abstract]    
Gross Recognized Assets 8,583 23,605
Gross Amounts Offset, Assets (1,649) (2,484)
Total financial assets 6,934 21,121
Derivative liability - noncurrent    
Derivative Liability [Abstract]    
Gross Recognized Liabilities 2,748 4,375
Gross Amounts Offset, Liabilities (1,649) (2,484)
Total financial liabilities $ 1,099 $ 1,891