Business Segments - Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenues from External Customers and Long-Lived Assets [Line Items]
Net income (loss) including noncontrolling interest	$ 204,000	$ 137,300	$ (27,000)	$ (266,800)	$ (162,700)	$ (266,600)	$ (324,400)	$ (508,700)	$ 47,528	$ (1,262,445)	$ 1,253,302
Revenues from external customers									2,299,281	1,967,341	2,829,053
Interest income and other (loss)									(16,771)	(17,303)	(22,520)
Interest expense, net of capitalization									(221,773)	(169,423)	(219,275)
Income tax expense (benefit)									(5,862)	(293,741)	14,683
Impairment of assets									196,296	1,206,284	0
Depreciation, depletion and amortization									795,105	987,239	1,147,842
Accretion of asset retirement obligations									46,613	42,136	40,506
Amortization of undeveloped leases									18,925	26,743	27,973
Deferred income tax (benefit) expense									(4,146)	(278,042)	28,530
Additions to property, plant, equipment									585,300	756,600	2,560,800
Total assets at year-end	10,304,940				10,620,852				10,304,940	10,620,852	11,718,500
Discontinued Operations
Revenues from External Customers and Long-Lived Assets [Line Items]
Net income (loss) including noncontrolling interest									(1,200)	(7,200)	1,064,500
Revenues from external customers									0	0	0
Interest income and other (loss)									0	0	0
Interest expense, net of capitalization									0	0	0
Income tax expense (benefit)									0	0	0
Impairment of assets									0	0
Depreciation, depletion and amortization									0	0	0
Accretion of asset retirement obligations									0	0	0
Amortization of undeveloped leases									0	0	0
Deferred income tax (benefit) expense									0	0	0
Additions to property, plant, equipment									0	0	0
Total assets at year-end	800				700				800	700	16,700
Corporate and Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Net income (loss) including noncontrolling interest									(668,000)	(120,300)	(271,800)
Revenues from external customers									(519,400)	207,900	3,500
Interest income and other (loss)									(6,500)	(9,100)	(6,700)
Interest expense, net of capitalization									(221,600)	(168,500)	(218,800)
Income tax expense (benefit)									(178,600)	(30,200)	(85,600)
Impairment of assets									7,000	14,100
Depreciation, depletion and amortization									13,000	22,300	22,600
Accretion of asset retirement obligations									0	0	0
Amortization of undeveloped leases									0	0	0
Deferred income tax (benefit) expense									(170,500)	(25,100)	(83,900)
Additions to property, plant, equipment									0	0	13,600
Total assets at year-end	1,220,800				1,032,900				1,220,800	1,032,900	1,046,200
Exploration and Production | Operating Segments
Revenues from External Customers and Long-Lived Assets [Line Items]
Net income (loss) including noncontrolling interest									716,700	(1,134,900)	460,600
Revenues from external customers									2,818,700	1,759,400	2,825,600
Interest income and other (loss)									(10,300)	(8,200)	(15,800)
Interest expense, net of capitalization									(200)	(900)	(500)
Income tax expense (benefit)									172,700	(263,500)	100,300
Impairment of assets									189,300	1,192,200
Depreciation, depletion and amortization									782,100	964,900	1,125,200
Accretion of asset retirement obligations									46,600	42,100	40,500
Amortization of undeveloped leases									18,900	26,700	28,000
Deferred income tax (benefit) expense									166,400	(252,900)	112,400
Additions to property, plant, equipment									585,300	756,600	2,547,200
Total assets at year-end	9,083,300				9,587,300				9,083,300	9,587,300	10,655,600
Exploration and Production | Operating Segments | UNITED STATES
Revenues from External Customers and Long-Lived Assets [Line Items]
Net income (loss) including noncontrolling interest									766,300	(1,014,300)	518,400
Revenues from external customers									2,337,500	1,411,800	2,367,000
Interest income and other (loss)									(11,600)	(9,900)	(13,400)
Interest expense, net of capitalization									0	0	0
Income tax expense (benefit)									183,900	(244,200)	115,600
Impairment of assets									0	1,152,500
Depreciation, depletion and amortization									616,500	749,400	878,700
Accretion of asset retirement obligations									36,900	36,600	34,400
Amortization of undeveloped leases									11,100	17,200	23,100
Deferred income tax (benefit) expense									176,300	(244,200)	111,800
Additions to property, plant, equipment									519,500	623,100	2,193,300
Total assets at year-end	6,591,600				6,915,500				6,591,600	6,915,500	8,043,300
Exploration and Production | Operating Segments | Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Net income (loss) including noncontrolling interest									(16,100)	(35,000)	(4,300)
Revenues from external customers									476,300	345,800	447,000
Interest income and other (loss)									(1,900)	800	(1,500)
Interest expense, net of capitalization									0	(500)	(100)
Income tax expense (benefit)									(1,700)	(21,400)	(2,900)
Impairment of assets									171,300	0
Depreciation, depletion and amortization									163,800	213,200	243,000
Accretion of asset retirement obligations									9,700	5,500	6,100
Amortization of undeveloped leases									200	400	1,300
Deferred income tax (benefit) expense									(1,900)	(10,600)	14,000
Additions to property, plant, equipment									52,700	118,300	284,100
Total assets at year-end	2,231,900				2,404,100				2,231,900	2,404,100	2,303,700
Exploration and Production | Operating Segments | Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Net income (loss) including noncontrolling interest									(33,500)	(85,600)	(53,500)
Revenues from external customers									4,900	1,800	11,600
Interest income and other (loss)									3,200	800	(900)
Interest expense, net of capitalization									(200)	(400)	(400)
Income tax expense (benefit)									(9,500)	2,100	(12,400)
Impairment of assets									18,000	39,700
Depreciation, depletion and amortization									1,800	2,300	3,500
Accretion of asset retirement obligations									0	0	0
Amortization of undeveloped leases									7,600	9,100	3,600
Deferred income tax (benefit) expense									(8,000)	1,900	(13,400)
Additions to property, plant, equipment									13,100	15,200	69,800
Total assets at year-end	$ 259,800				$ 267,700				$ 259,800	$ 267,700	$ 308,600