Consolidated Statements of Cash Flows (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cash flow from operating activities:
Net income (loss)	$ 573,333,000	$ 285,527,000	$ (75,156,000)
Adjustments needed to reconcile to net cash flow provided by operations:
Depletion, depreciation and amortization	409,196,000	434,307,000	238,323,000
Deferred income taxes	342,463,000	160,349,000	(51,644,000)
Gain on sale of interests in Genesis	0	(101,537,000)	0
Stock-based compensation	33,190,000	35,366,000	35,581,000
Non-cash fair value derivative adjustments	(50,008,000)	(55,445,000)	383,072,000
Loss on early extinguishment of debt	16,131,000	0	0
Founder's retirement compensation	0	0	6,350,000
Debt issuance costs and discount amortization	16,954,000	17,876,000	7,215,000
Impairment of assets	22,951,000	0	0
Other, net	(4,302,000)	(2,144,000)	(3,704,000)
Changes in assets and liabilities, net of effects from acquisitions:
Accrued production receivable	(74,781,000)	2,426,000	(52,863,000)
Trade and other receivables	(55,470,000)	24,977,000	12,681,000
Other current and long-term assets	(15,817,000)	(4,119,000)	(559,000)
Accounts payable and accrued liabilities	(35,462,000)	48,549,000	25,673,000
Oil and natural gas production payable	54,391,000	15,565,000	4,385,000
Other liabilities	(27,955,000)	(5,886,000)	1,245,000
Net cash provided by operating activities	1,204,814,000	855,811,000	530,599,000
Cash flow used for investing activities:
Oil and natural gas capital expenditures	(1,082,853,000)	(671,574,000)	(343,351,000)
Acquisitions of oil and natural gas properties	(35,305,000)	(25,672,000)	(452,795,000)
Cash paid in Encore Merger and Riley Ridge acquisitions	(199,263,000)	(947,241,000)	0
CO2 capital expenditures	(84,789,000)	(93,556,000)	(100,358,000)
Pipelines and plants capital expenditures	(236,133,000)	(207,536,000)	(566,014,000)
Purchases of other assets	(28,838,000)	(28,684,000)	(13,591,000)
Net proceeds from sale of interests in Genesis	0	162,619,000	0
Net proceeds from sales of oil and natural gas properties and equipment	69,370,000	1,458,029,000	516,814,000
Other	(8,147,000)	(1,165,000)	(10,419,000)
Net cash used for investing activities	(1,605,958,000)	(354,780,000)	(969,714,000)
Cash flow from financing activities:
Bank repayments	(330,000,000)	(1,530,000,000)	(856,000,000)
Bank borrowings	715,000,000	1,114,000,000	906,000,000
Repayment of senior subordinated notes	(525,000,000)	(609,424,000)	0
Premium paid on repayment of senior subordinated notes	(13,137,000)	(7,213,000)	0
Net proceeds from issuance of senior subordinated notes	400,000,000	1,000,000,000	389,827,000
Net proceeds from issuance of common stock	15,920,000	13,065,000	12,991,000
Costs of debt financing	(13,123,000)	(76,251,000)	(10,080,000)
ENP distributions to noncontrolling interest	0	(36,738,000)	0
Stock repurchase program	(195,227,000)	0	0
Other	(16,465,000)	(7,192,000)	(101,000)
Net cash provided by (used for) financing activities	37,968,000	(139,753,000)	442,637,000
Net increase in cash and cash equivalents	(363,176,000)	361,278,000	3,522,000
Cash and cash equivalents at beginning of year	381,869,000	20,591,000	17,069,000
Cash and cash equivalents at end of year	$ 18,693,000	$ 381,869,000	$ 20,591,000