Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities
Net income (loss)	$ (4,385,448)	$ 635,491	$ 409,597
Adjustments to reconcile net income (loss) to cash flows from operating activities
Depletion, depreciation, and amortization	531,660	592,972	509,943
Write-down of oil and natural gas properties	4,939,600	0	0
Impairment of goodwill	1,261,512	0	0
Deferred income taxes	(1,932,179)	429,973	222,526
Stock-based compensation	30,604	30,513	33,003
Commodity derivatives expense (income)	(147,999)	(555,255)	41,024
Receipt (payment) on settlements of commodity derivatives	511,699	1,421	(662)
Loss on early extinguishment of debt	0	113,908	44,651
Amortization of debt issuance costs and discounts	9,121	13,476	14,023
Other, net	343	6,311	(2,318)
Changes in assets and liabilities, net of effects from acquisitions
Accrued production receivable	81,213	80,285	(15,085)
Trade and other receivables	67,047	(78,469)	4,981
Other current and long-term assets	241	3,174	10,462
Accounts payable and accrued liabilities	(55,234)	501	91,816
Oil and natural gas production payable	(40,833)	(46,506)	12,731
Other liabilities	(7,043)	(4,970)	(15,497)
Net cash provided by operating activities	864,304	1,222,825	1,361,195
Cash flows from investing activities
Oil and natural gas capital expenditures	(476,398)	(946,846)	(900,221)
Acquisitions of oil and natural gas properties	(21,876)	(8,773)	(9,243)
CO2 capital expenditures	(26,301)	(48,134)	(93,744)
Pipelines and plants capital expenditures	(31,728)	(72,151)	(184,286)
Purchases of other assets	(5,492)	(3,197)	(65,987)
Net proceeds from sales of oil and natural gas properties and equipment	563	3,453	8,037
Other	11,047	(1,107)	(29,865)
Net cash used in investing activities	(550,185)	(1,076,755)	(1,275,309)
Cash flows from financing activities
Bank repayments	(1,862,000)	(2,609,000)	(1,550,000)
Bank borrowings	1,642,000	2,664,000	1,190,000
Repayment of senior subordinated notes	(485)	(997,345)	(651,270)
Premium paid on repayment of senior subordinated notes	0	(101,342)	(36,475)
Proceeds from issuance of senior subordinated notes	0	1,250,000	1,200,000
Costs of debt financing	(1,668)	(24,407)	(20,161)
Common stock repurchase program	(11,759)	(211,356)	(281,958)
Cash dividends paid	(65,426)	(87,044)	0
Other	(35,122)	(18,610)	(22,346)
Net cash used in financing activities	(334,460)	(135,104)	(172,210)
Net increase (decrease) in cash and cash equivalents	(20,341)	10,966	(86,324)
Cash and cash equivalents at beginning of year	23,153	12,187	98,511
Cash and cash equivalents at end of year	$ 2,812	$ 23,153	$ 12,187