Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Cash flows from operating activities
Net income	$ 87,571	$ 113,467
Adjustments to reconcile net income to cash flow from operating activities
Depletion, depreciation, and amortization	112,898	120,895
Deferred income taxes	43,845	37,137
Stock-based compensation	7,908	7,913
Noncash fair value derivative adjustments	11,957	44,113
Loss on early extinguishment of debt	44,223	0
Amortization of debt issuance costs and discounts	3,736	3,674
Impairment of assets	0	17,300
Other, net	3,608	7,725
Changes in assets and liabilities, net of effects from acquisitions:
Accrued production receivable	344	(8,863)
Trade and other receivables	(13,815)	9,162
Other current and long-term assets	(4,756)	676
Accounts payable and accrued liabilities	(33,337)	(32,861)
Oil and natural gas production payable	12,424	(470)
Other liabilities	(7,430)	(28,214)
Net cash provided by operating activities	269,176	291,654
Cash flow used in investing activities
Oil and natural gas capital expenditures	(226,917)	(302,246)
Acquisitions of oil and natural gas properties	(101)	(592)
CO2 capital expenditures	(27,014)	(30,693)
Pipelines and plants capital expenditures	(50,416)	(60,441)
Purchases of other assets	(14,867)	(4,945)
Net proceeds from sales of oil and natural gas properties and equipment	663	26,572
Proceeds from sale of short-term investments	0	83,545
Other	(1,994)	(83)
Net cash used for investing activities	(320,646)	(288,883)
Cash flow provided by financing activities:
Bank repayments	(820,000)	(150,000)
Bank borrowings	395,000	210,000
Repayment of senior subordinated notes	(613,064)	0
Premium paid on repayment of senior subordinated notes	(34,660)	0
Proceeds from issuance of senior subordinated notes	1,200,000	0
Costs of debt financing	(20,000)	(11)
Common stock repurchase program	(81,402)	0
Other	(10,646)	(4,087)
Net cash provided by financing activities	15,228	55,902
Net increase (decrease) in cash and cash equivalents	(36,242)	58,673
Cash and cash equivalents at beginning of period	98,511	18,693
Cash and cash equivalents at end of period	$ 62,269	$ 77,366