Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Segment Reporting Information [Line Items]
Total Assets	$ 9,942,578		$ 9,942,578		$ 10,308,952
External Revenues	959,645	$ 1,303,425	2,615,949	$ 2,957,443
Income (Loss)	277,804	574,076	583,974	918,094
Continuing operations
Segment Reporting Information [Line Items]
Total Assets	9,941,500		9,941,500
External Revenues	959,600	1,303,400	2,615,900	2,957,400
Income (Loss)	278,200	574,500	584,700	920,000
Discontinued operations, net of tax
Segment Reporting Information [Line Items]
Total Assets	1,100		1,100
External Revenues	0	0	0	0
Income (Loss)	(400)	(400)	(700)	(1,900)
Corporate
Segment Reporting Information [Line Items]
Total Assets	714,900		714,900
External Revenues	3,200	115,200	3,300	(302,600)
Income (Loss)	(30,100)	57,400	(105,400)	(363,700)
Exploration and Production | Operating Segments
Segment Reporting Information [Line Items]
Total Assets	9,226,600		9,226,600
External Revenues	956,400	1,188,200	2,612,600	3,260,000
Income (Loss)	308,300	517,100	690,100	1,283,700
Exploration and Production | Operating Segments | United States
Segment Reporting Information [Line Items]
Total Assets	6,925,000		6,925,000
External Revenues	823,700	973,800	2,202,200	2,659,200
Income (Loss)	310,300	481,500	705,200	1,225,900
Exploration and Production | Operating Segments | Canada
Segment Reporting Information [Line Items]
Total Assets	2,074,700		2,074,700
External Revenues	129,300	209,600	403,300	582,300
Income (Loss)	10,500	41,400	34,900	111,300
Exploration and Production | Operating Segments | Other
Segment Reporting Information [Line Items]
Total Assets	226,900		226,900
External Revenues	3,400	4,800	7,100	18,500
Income (Loss)	$ (12,500)	$ (5,800)	$ (50,000)	$ (53,500)