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	Sep. 30, 2018	Dec. 31, 2017
Derivative asset - current
Derivative Asset [Abstract]
Gross Recognized Assets	$ 0	$ 184
Gross Amounts Offset, Assets	0	0
Total financial assets	0	184
Derivative liability - current
Derivative Liability [Abstract]
Gross Recognized Liabilities	25,200	11,805
Gross Amounts Offset, Liabilities	(1,809)	0
Total financial liabilities	23,391	11,805
Derivative liability - noncurrent
Derivative Liability [Abstract]
Gross Recognized Liabilities	10,025	1,826
Gross Amounts Offset, Liabilities	(6)	0
Total financial liabilities	$ 10,019	$ 1,826