Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Cash flow from operating activities
Net income (loss)	$ 3,110	$ 217,551
Adjustments to reconcile net income (loss) to cash flow from operating activities
Depletion, depreciation, and amortization	289,294	239,805
Deferred income taxes	1,611	128,342
Stock-based compensation	17,217	15,671
Commodity derivative expense (income)	251,440	(33,572)
Settlements of commodity derivatives	(77,341)	0
Loss on early extinguishment of debt	113,908	44,651
Amortization of debt issuance costs and discounts	6,978	7,139
Other, net	(3,402)	5,097
Changes in assets and liabilities, net of effects from acquisitions
Accrued production receivable	(25,236)	(6,769)
Trade and other receivables	12,921	3,117
Other current and long-term assets	(2,989)	(9,171)
Accounts payable and accrued liabilities	(36,178)	86,969
Oil and natural gas production payable	(2,033)	20,222
Other liabilities	(4,595)	(12,308)
Net cash provided by operating activities	544,705	706,744
Cash flow from investing activities
Oil and natural gas capital expenditures	(451,564)	(486,163)
CO2 capital expenditures	(29,901)	(44,708)
Pipelines and plants capital expenditures	(34,530)	(97,480)
Purchases of other assets	(3,620)	(22,825)
Net proceeds from sales of oil and natural gas properties and equipment	1,736	5,496
Other	977	(19,893)
Net cash used in investing activities	(516,902)	(665,573)
Cash flows from financing activities
Bank repayments	(1,315,000)	(970,000)
Bank borrowings	1,420,000	530,000
Repayment of senior subordinated notes	(997,345)	(651,270)
Premium paid on repayment of senior subordinated notes	(101,342)	(36,475)
Proceeds from issuance of senior subordinated notes	1,250,000	1,200,000
Costs of debt financing	(17,551)	(20,026)
Common stock repurchase program	(211,356)	(100,423)
Dividends paid	(43,461)	0
Other	(11,889)	(15,623)
Net cash used in financing activities	(27,944)	(63,817)
Net decrease in cash and cash equivalents	(141)	(22,646)
Cash and cash equivalents at beginning of period	12,187	98,511
Cash and cash equivalents at end of period	$ 12,046	$ 75,865