Consolidated Statements of Cash Flows - USD ($)	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2020	Sep. 18, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities
Net income (loss)	$ (50,658,000)	$ (1,432,578,000)	$ 216,959,000	$ 322,698,000
Adjustments to reconcile net income (loss) to cash flows from operating activities
Noncash reorganization items, net	0	810,909,000	0	0
Depletion, depreciation, and amortization	45,812,000	188,593,000	233,816,000	216,449,000
Write-down of oil and natural gas properties	1,006,000	996,658,000	0	0
Deferred income taxes	(2,556,000)	(408,869,000)	100,471,000	103,234,000
Stock-based compensation	8,212,000	4,111,000	12,470,000	11,951,000
Commodity derivatives expense (income)	61,902,000	(102,032,000)	70,078,000	(21,087,000)
Receipt (payment) on settlements of commodity derivatives	21,089,000	81,396,000	23,606,000	(175,248,000)
Gain on debt extinguishment	0	(18,994,000)	(155,998,000)	0
Debt issuance costs and discounts	799,000	11,571,000	12,303,000	6,246,000
Other, net	(2,349,000)	439,000	(8,596,000)	(4,725,000)
Changes in assets and liabilities, net of effects from acquisitions
Accrued production receivable	21,411,000	26,575,000	(13,619,000)	20,547,000
Trade and other receivables	15,567,000	(22,343,000)	9,379,000	16,094,000
Other current and long-term assets	(1,795,000)	743,000	7,629,000	(6,827,000)
Accounts payable and accrued liabilities	(67,167,000)	(16,102,000)	(3,275,000)	13,008,000
Oil and natural gas production payable	(6,912,000)	(6,792,000)	2,170,000	(15,300,000)
Other liabilities	(4,035,000)	123,000	(13,250,000)	42,645,000
Net cash provided by operating activities	40,326,000	113,408,000	494,143,000	529,685,000
Cash flows from investing activities
Oil and natural gas capital expenditures	(17,964,000)	(99,582,000)	(262,005,000)	(316,647,000)
CO2 capital expenditures	(269,000)	(196,000)	(3,154,000)	(5,878,000)
Pipelines and plants capital expenditures	(618,000)	(11,601,000)	(27,319,000)	(23,108,000)
Net proceeds from sales of oil and natural gas properties and equipment	938,000	41,322,000	10,196,000	7,762,000
Other	16,029,000	12,943,000	12,590,000	4,595,000
Net cash used in investing activities	(1,884,000)	(57,114,000)	(269,692,000)	(333,276,000)
Cash flows from financing activities
Bank repayments	(190,000,000)	(551,000,000)	(925,791,000)	(1,982,653,000)
Bank borrowings	120,000,000	691,000,000	925,791,000	1,507,653,000
Interest payments treated as a reduction of debt	0	(46,417,000)	(85,303,000)	(79,606,000)
Proceeds from issuance of senior secured notes	0	0	0	450,000,000
Cash paid in conjunction with debt exchange	0	0	(136,427,000)	0
Cash paid in conjunction with debt repurchases	0	(14,171,000)	0	0
Costs of debt financing	(8,000)	(12,482,000)	(11,065,000)	(16,060,000)
Pipeline financing and capital lease debt repayments	(22,938,000)	(51,792,000)	(13,908,000)	(23,300,000)
Other	1,638,000	(9,363,000)	348,000	(13,486,000)
Net cash provided by (used in) financing activities	(91,308,000)	5,775,000	(246,355,000)	(157,452,000)
Net increase (decrease) in cash, cash equivalents, and restricted cash	(52,866,000)	62,069,000	(21,904,000)	38,957,000
Cash, cash equivalents, and restricted cash at beginning of period	95,114,000	33,045,000	54,949,000	15,992,000
Cash, cash equivalents, and restricted cash at end of period	$ 42,248,000	$ 95,114,000	$ 33,045,000	$ 54,949,000