Segment Information - Reconciliation of Segment Information, Revenue and Other Operating Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue, Major Customer [Line Items]
Gain (Loss) on Commodity Derivative Instruments	$ 213,913	$ 18,005	$ 240,118	$ 78,752
Other Operating Income	3,316	3,903	9,436	23,146
Total Revenue	529,997	397,126	1,413,460	1,294,979
Operating Segments
Revenue, Major Customer [Line Items]
Total Segment Revenue from Contracts with External Customers	$ 312,768	$ 375,218	$ 1,163,906	$ 1,193,081