Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities
Net income (loss)	$ 322,698	$ 163,152	$ (976,177)
Adjustments to reconcile net income (loss) to cash flows from operating activities
Depletion, depreciation, and amortization	216,449	207,713	846,043
Write-down of oil and natural gas properties	0	0	810,921
Deferred income taxes	103,234	(95,779)	(543,385)
Stock-based compensation	11,951	15,154	14,995
Commodity derivatives expense (income)	(21,087)	77,576	127,944
Receipt (payment) on settlements of commodity derivatives	(175,248)	(47,795)	84,181
Gain on debt extinguishment	0	0	(115,095)
Debt issuance costs and discounts	6,246	6,191	17,006
Other, net	(4,725)	3,112	(2,161)
Changes in assets and liabilities, net of effects from acquisitions
Accrued production receivable	20,547	(21,398)	(24,290)
Trade and other receivables	16,094	(4,421)	35,923
Other current and long-term assets	(6,827)	(1,722)	(8,661)
Accounts payable and accrued liabilities	13,008	(24,710)	(34,240)
Oil and natural gas production payable	(15,300)	(3,997)	(6,752)
Other liabilities	42,645	(5,933)	(7,029)
Net cash provided by operating activities	529,685	267,143	219,223
Cash flows from investing activities
Oil and natural gas capital expenditures	(316,647)	(262,867)	(243,027)
Acquisitions of oil and natural gas properties	(541)	(88,886)	(1,310)
CO2 capital expenditures	(5,878)	(2,159)	(2,321)
Pipelines and plants capital expenditures	(23,108)	(2,540)	(2,666)
Net proceeds from sales of oil and natural gas properties and equipment	7,762	1,696	47,725
Other	5,136	(2,058)	(3,064)
Net cash used in investing activities	(333,276)	(356,814)	(204,663)
Cash flows from financing activities
Bank repayments	(1,982,653)	(1,589,000)	(1,730,500)
Bank borrowings	1,507,653	1,763,000	1,856,500
Interest payments treated as a reduction of debt	(79,606)	(50,349)	(25,835)
Proceeds from issuance of senior secured notes	450,000	0	0
Repayment or repurchases of senior subordinated notes	0	(2,503)	(76,708)
Cost of debt financing	(16,060)	(6,289)	(9,574)
Pipeline financing and capital lease debt repayments	(23,300)	(27,462)	(28,849)
Other	(13,486)	1,216	(46)
Net cash provided by (used in) financing activities	(157,452)	88,613	(15,012)
Net increase (decrease) in cash, cash equivalents, and restricted cash	38,957	(1,058)	(452)
Cash, cash equivalents, and restricted cash at beginning of year	15,992	17,050	17,502
Cash, cash equivalents, and restricted cash at end of year	$ 54,949	$ 15,992	$ 17,050