Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $)	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Cash flows from operating activities
Net income	$ 410,699,000	$ 520,726,000
Adjustments needed to reconcile to net cash flow provided by operations
Depletion, depreciation, and amortization	390,119,000	299,067,000
Deferred income taxes	216,959,000	317,601,000
Stock-based compensation	22,662,000	27,520,000
Noncash fair value derivative adjustments	(19,757,000)	(217,008,000)
Loss on early extinguishment of debt	0	16,131,000
Amortization of debt issuance costs and discounts	11,021,000	13,280,000
Impairment of assets	17,515,000	0
Other, net	15,087,000	(4,340,000)
Changes in operating assets and liabilities:
Accrued production receivable	3,221,000	(45,017,000)
Trade and other receivables	11,010,000	(38,607,000)
Other current and long-term assets	8,218,000	(11,587,000)
Accounts payable and accrued liabilities	(30,127,000)	(65,407,000)
Oil and natural gas production payable	5,014,000	40,819,000
Other liabilities	(35,515,000)	(14,086,000)
Net cash provided by operating activities	1,026,126,000	839,092,000
Cash flows from investing activities
Oil and natural gas capital expenditures	(848,618,000)	(741,256,000)
Acquisitions of oil and natural gas properties	(155,636,000)	(34,291,000)
Cash paid in Riley Ridge acquisition	0	(199,233,000)
CO2 capital expenditures	(93,945,000)	(62,546,000)
Pipelines and plants capital expenditures	(231,459,000)	(142,406,000)
Purchases of other assets	(18,666,000)	(25,211,000)
Net proceeds from sales of oil and natural gas properties and equipment	33,973,000	47,598,000
Proceeds from sale of short-term investments	83,545,000	0
Other	(7,166,000)	(907,000)
Net cash used for investing activities	(1,237,972,000)	(1,158,252,000)
Cash flows from financing activities
Bank repayments	(970,000,000)	(255,000,000)
Bank borrowings	1,210,000,000	365,000,000
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	12,579,000	12,348,000
Costs of debt financing	(17,000)	(13,104,000)
Common stock repurchase program	(16,747,000)	0
Other	(18,628,000)	(9,453,000)
Net cash provided by (used for) financing activities	217,187,000	(38,346,000)
Net increase (decrease) in cash and cash equivalents	5,341,000	(357,506,000)
Cash and cash equivalents at beginning of period	18,693,000	381,869,000
Cash and cash equivalents at end of period	$ 24,034,000	$ 24,363,000