Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Cash flow from operating activities:
Net income	$ 58,310	$ 87,571
Adjustments to reconcile net income to cash flow from operating activities:
Depletion, depreciation, and amortization	141,130	112,898
Deferred income taxes	30,175	43,845
Stock-based compensation	8,346	7,908
Commodity derivative expense (income)	76,669	11,929
Settlements of commodity derivatives	(27,169)	0
Loss on early extinguishment of debt	0	44,223
Amortization of debt issuance costs and discounts	3,520	3,736
Other, net	(2,297)	3,636
Changes in assets and liabilities, net of effects from acquisitions:
Accrued production receivable	(24,937)	344
Trade and other receivables	6,372	(13,815)
Other current and long-term assets	(5,459)	(4,756)
Accounts payable and accrued liabilities	(52,580)	(33,337)
Oil and natural gas production payable	3,916	12,424
Other liabilities	(1,138)	(7,430)
Net cash provided by operating activities	214,858	269,176
Cash flow used in investing activities:
Oil and natural gas capital expenditures	(198,237)	(226,917)
Acquisitions of oil and natural gas properties	0	(101)
CO2 capital expenditures	(15,909)	(27,014)
Pipelines and plants capital expenditures	(22,597)	(50,416)
Purchases of other assets	(1,645)	(14,867)
Net proceeds from sales of oil and natural gas properties and equipment	457	663
Other	1,177	(1,994)
Net cash used in investing activities	(236,754)	(320,646)
Cash flow provided by financing activities:
Bank repayments	(815,000)	(820,000)
Bank borrowings	1,075,000	395,000
Repayment of senior subordinated notes	0	(613,064)
Premium paid on repayment of senior subordinated notes	0	(34,660)
Proceeds from issuance of senior subordinated notes	0	1,200,000
Costs of debt financing	0	(20,000)
Common stock repurchase program	(211,356)	(81,402)
Dividends paid	(21,727)	0
Other	(9,316)	(10,646)
Net cash provided by financing activities	17,601	15,228
Net decrease in cash and cash equivalents	(4,295)	(36,242)
Cash and cash equivalents at beginning of period	12,187
Cash and cash equivalents at end of period	$ 7,892	$ 62,269