Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $)	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010
Cash flows from operating activities
Consolidated net income (loss)	$ 245,056,000	$ 250,533,000
Adjustments needed to reconcile to net cash provided by operating activities
Depletion, depreciation, and amortization	197,089,000	211,081,000
Deferred income taxes	144,620,000	150,694,000
Gain on sale of interests in Genesis	0	(101,540,000)
Stock-based compensation	18,132,000	17,130,000
Non-cash fair value derivative adjustments	(11,508,000)	(226,899,000)
Loss on early extinguishment of debt	16,131,000	0
Other, net	5,755,000	5,871,000
Changes in operating assets and liabilities:
Accrued production receivable	(35,068,000)	52,075,000
Trade and other receivables	(28,258,000)	10,058,000
Other assets	(2,920,000)	(3,134,000)
Accounts payable and accrued liabilities	(48,471,000)	12,066,000
Oil and natural gas production payable	30,135,000	11,236,000
Increase (Decrease) in Other Operating Liabilities	(7,340,000)	(4,880,000)
Net cash provided by operating activities	523,353,000	384,291,000
Cash flows used for investing activities
Oil and natural gas capital expenditures	(471,601,000)	(317,173,000)
Acquisitions of oil and natural gas properties	(32,482,000)	(24,243,000)
Cash paid in Encore Merger, net of cash acquired	0	(801,489,000)
CO2 and other non-hydrocarbon gases capital expenditures	(31,731,000)	(44,274,000)
Pipelines and plants capital expenditures	(98,669,000)	(108,177,000)
Net proceeds from sales of oil and natural gas properties and equipment	0	881,344,000
Net proceeds from sale of interests in Genesis	0	162,622,000
Payments for (proceeds from) other investing activities	1,643,000	(7,224,000)
Net cash used for investing activities	(632,840,000)	(258,614,000)
Cash flows from financing activities
Bank repayments	(130,000,000)	(1,514,000,000)
Bank borrowings	130,000,000	1,149,000,000
Repayment of senior subordinated notes	(525,000,000)	(609,424,000)
Premium paid on repayment of senior subordinated notes	(13,137,000)	(7,214,000)
Net proceeds from issuance of senior subordinated notes	400,000,000	1,000,000,000
Net proceeds from issuance of common stock	9,203,000	5,540,000
Costs of debt financing	(13,274,000)	(76,232,000)
ENP distributions to noncontrolling interest	0	(12,209,000)
Other	(8,382,000)	(14,255,000)
Net cash provided by (used for) financing activities	(150,590,000)	(78,794,000)
Net increase (decrease) in cash and cash equivalents	(260,077,000)	46,883,000
Cash and cash equivalents at beginning of period	381,869,000	20,591,000
Cash and cash equivalents at end of period	$ 121,792,000	$ 67,474,000