Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $)	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Cash flows from operating activities
Consolidated net income (loss)	$ 520,726,000	$ 281,767,000
Adjustments needed to reconcile to net cash provided by operating activities
Depletion, depreciation, and amortization	299,067,000	322,683,000
Deferred income taxes	317,601,000	167,289,000
Gain on sale of interests in Genesis	0	(101,537,000)
Stock-based compensation	27,520,000	27,326,000
Non-cash fair value derivative adjustments	(217,092,000)	(185,009,000)
Loss on early extinguishment of debt	16,131,000	0
Other, net	9,024,000	14,254,000
Changes in operating assets and liabilities:
Accrued production receivable	(45,017,000)	48,453,000
Trade and other receivables	(53,012,000)	20,548,000
Other assets	2,818,000	1,106,000
Accounts payable and accrued liabilities	(65,407,000)	8,257,000
Oil and natural gas production payable	40,819,000	10,553,000
Increase (Decrease) in Other Operating Liabilities	(14,086,000)	(22,915,000)
Net cash provided by operating activities	839,092,000	592,775,000
Cash flows used for investing activities
Oil and natural gas capital expenditures	(741,256,000)	(500,062,000)
Acquisitions of oil and natural gas properties	(34,291,000)	(24,390,000)
Cash paid to acquire a business, net of cash acquired	(199,233,000)	(813,894,000)
CO2 and other non-hydrocarbon gases capital expenditures	(65,866,000)	(67,328,000)
Pipelines and plants capital expenditures	(142,406,000)	(169,157,000)
Net proceeds from sales of oil and natural gas properties and equipment	47,598,000	909,986,000
Net proceeds from sale of interests in Genesis	0	162,619,000
Payments for (proceeds from) other investing activities	(22,798,000)	(17,927,000)
Net cash used for investing activities	(1,158,252,000)	(520,153,000)
Cash flows from financing activities
Bank repayments	(255,000,000)	(1,519,000,000)
Bank borrowings	365,000,000	1,229,000,000
Repayment of senior subordinated notes	(525,000,000)	(609,424,000)
Premium paid on repayment of senior subordinated notes	(13,137,000)	(7,213,000)
Net proceeds from issuance of senior subordinated notes	400,000,000	1,000,000,000
Net proceeds from issuance of common stock	12,348,000	8,614,000
Costs of debt financing	(13,104,000)	(76,232,000)
ENP distributions to noncontrolling interest	0	(24,513,000)
Other	(9,453,000)	(8,100,000)
Net cash provided by (used for) financing activities	(38,346,000)	(6,868,000)
Net increase (decrease) in cash and cash equivalents	(357,506,000)	65,754,000
Cash and cash equivalents at beginning of period	381,869,000	20,591,000
Cash and cash equivalents at end of period	$ 24,363,000	$ 86,345,000