Revenue from Contracts with Customers (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	$ 758,829	$ 285,745	$ 1,351,356	$ 886,303
(Loss) gain on crude contracts	(226,245)	(75,880)	(440,630)	324,792
Gain on sale of assets and other income	17,059	1,677	18,902	4,175
Total revenues and other income	549,643	211,542	929,628	1,215,270
Net crude oil and condensate revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	656,810	227,349	1,147,606	755,418
Net natural gas liquids revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	23,602	8,616	45,171	21,179
Net natural gas revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	78,417	49,780	158,579	109,706
United States | Net crude oil and condensate revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	183,267	54,550	297,757	185,786
United States | Net natural gas liquids revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	9,596	3,876	17,124	9,379
United States | Net natural gas revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	6,872	4,090	13,315	9,648
United States Offshore | Net crude oil and condensate revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	411,076	150,253	739,417	497,225
United States Offshore | Net natural gas liquids revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	10,766	3,464	20,820	8,490
United States Offshore | Net natural gas revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	17,273	10,665	39,411	25,660
Canada     | Net crude oil and condensate revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	30,695	11,527	60,598	34,910
Canada     | Net natural gas liquids revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	3,240	1,276	7,227	3,310
Canada     | Net natural gas revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	54,272	35,025	105,853	74,398
Canada Offshore | Net crude oil and condensate revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	31,772	11,077	49,834	35,691
Other | Net crude oil and condensate revenue
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	$ 0	$ (58)	$ 0	$ 1,806