Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $)	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Cash flows from operating activities
Net income	$ 325,332,000	$ 245,056,000
Adjustments needed to reconcile to net cash flow provided by operations
Depletion, depreciation, and amortization	253,184,000	197,089,000
Deferred income taxes	167,289,000	144,620,000
Stock-based compensation	15,249,000	18,132,000
Noncash fair value derivative adjustments	(87,686,000)	(11,451,000)
Loss on early extinguishment of debt	0	16,131,000
Amortization of debt issuance costs and discounts	7,347,000	9,613,000
Impairment of assets	17,515,000	0
Other, net	15,835,000	(3,915,000)
Changes in operating assets and liabilities:
Accrued production receivable	35,466,000	(35,068,000)
Trade and other receivables	(10,769,000)	(10,142,000)
Other current and long-term assets	6,851,000	(21,036,000)
Accounts payable and accrued liabilities	28,256,000	(48,471,000)
Oil and natural gas production payable	(7,985,000)	30,135,000
Other liabilities	(33,264,000)	(7,340,000)
Net cash provided by operating activities	732,620,000	523,353,000
Cash flows from investing activities
Oil and natural gas capital expenditures	(574,008,000)	(471,601,000)
Acquisitions of oil and natural gas properties	(154,366,000)	(32,482,000)
CO2 capital expenditures	(53,313,000)	(32,042,000)
Pipelines and plants capital expenditures	(169,675,000)	(98,237,000)
Purchases of other assets	(10,748,000)	(20,372,000)
Net proceeds from sales of oil and natural gas properties and equipment	32,302,000	18,432,000
Proceeds from sale of short-term investments	83,545,000	0
Other	(2,961,000)	3,462,000
Net cash used for investing activities	(849,224,000)	(632,840,000)
Cash flows from financing activities
Bank repayments	(400,000,000)	(130,000,000)
Bank borrowings	535,000,000	130,000,000
Repayment of senior subordinated notes	0	(525,000,000)
Premium paid on repayment of senior subordinated notes	0	(13,137,000)
Net proceeds from issuance of senior subordinated notes	0	400,000,000
Net proceeds from issuance of common stock	8,055,000	9,203,000
Costs of debt financing	(11,000)	(13,274,000)
Other	(17,020,000)	(8,382,000)
Net cash provided by (used for) financing activities	126,024,000	(150,590,000)
Net increase (decrease) in cash and cash equivalents	9,420,000	(260,077,000)
Cash and cash equivalents at beginning of period	18,693,000	381,869,000
Cash and cash equivalents at end of period	$ 28,113,000	$ 121,792,000