CONSOLIDATED STATEMENT OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
OPERATING REVENUES
Total revenues from contracts with customers	$ 1,405,220	$ 1,985,469	$ 2,143,716
Gain on derivative instruments	61,404	80,808	44,432
Total operating revenues	1,466,624	2,066,277	2,188,148
OPERATING EXPENSES
Direct operations	73,403	76,958	69,646
Taxes other than income	14,380	17,053	22,642
Exploration	15,419	20,270	113,820
Depreciation, depletion and amortization	390,903	405,733	417,479
General and administrative	105,391	94,870	96,641
TOTAL OPERATING EXPENSES	1,170,598	1,189,561	1,401,157
(Loss) earnings on equity method investments	(59)	80,496	1,137
(Loss) gain on sale of assets	(491)	(1,462)	(16,327)
INCOME FROM OPERATIONS	295,476	955,750	771,801
Interest expense, net	54,124	54,952	73,201
Other expense	229	574	463
Income before income taxes	241,123	900,224	698,137
Income tax expense	40,594	219,154	141,094
NET INCOME	$ 200,529	$ 681,070	$ 557,043
Earnings per share
Basic (in dollars per share)	$ 0.50	$ 1.64	$ 1.25
Diluted (in dollars per share)	$ 0.50	$ 1.63	$ 1.24
Weighted-average common shares outstanding
Basic (in shares)	398,521	415,514	445,538
Diluted (in shares)	400,522	417,451	447,568
Natural gas
OPERATING REVENUES
Total revenues from contracts with customers	$ 1,404,989	$ 1,985,240	$ 1,881,150
Crude oil and condensate
OPERATING REVENUES
Total revenues from contracts with customers	0	0	48,722
Brokered natural gas
OPERATING REVENUES
Total revenues from contracts with customers	0	0	209,530
OPERATING EXPENSES
Operating expenses	0	0	184,198
Other
OPERATING REVENUES
Total revenues from contracts with customers	231	229	4,314
Transportation and gathering
OPERATING EXPENSES
Operating expenses	$ 571,102	$ 574,677	$ 496,731