Segment Information - Reconciliation of Segment Information, Revenue and Other Operating Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue, Major Customer [Line Items]
(Loss) Gain on Commodity Derivative Instruments	$ (168,834)	$ 213,913	$ (116,995)	$ 240,118
Other Operating Income	4,466	3,317	13,177	9,436
Total Revenue and Other Operating Income	66,075	529,997	631,275	1,413,460
Operating Segments
Revenue, Major Customer [Line Items]
Total Segment Revenue from Contracts with External Customers	$ 230,443	$ 312,767	$ 735,093	$ 1,163,906