Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash flow from operating activities
Net income	$ 409,597	$ 525,360	$ 573,333
Adjustments to reconcile net income to cash flow from operating activities
Depletion, depreciation and amortization	509,943	507,538	409,196
Deferred income taxes	222,526	255,743	342,463
Stock-based compensation	33,003	29,310	33,190
Commodity derivatives expense (income)	41,024	(4,834)	(52,497)
Cash receipt (payment) on settlements of commodity derivatives	(662)	17,880	2,377
Loss on early extinguishment of debt	44,651	0	16,131
Amortization of debt issuance costs and discounts	14,023	14,695	16,954
Impairment of assets	0	17,515	22,951
Other, net	(2,318)	16,917	(4,190)
Changes in assets and liabilities, net of effects from acquisitions
Accrued production receivable	(15,085)	36,234	(74,781)
Trade and other receivables	4,981	45,836	(55,470)
Other current and long-term assets	10,462	7,688	(15,817)
Accounts payable and accrued liabilities	91,816	5,828	(35,462)
Oil and natural gas production payable	12,731	(23,460)	54,391
Other liabilities	(15,497)	(41,359)	(27,955)
Net cash provided by operating activities	1,361,195	1,410,891	1,204,814
Cash flow used for investing activities
Oil and natural gas capital expenditures	(900,221)	(1,122,615)	(1,082,853)
Acquisitions of oil and natural gas properties	(9,243)	(156,082)	(35,305)
Cash paid in Riley Ridge acquisition	0	0	(199,263)
Bakken exchange transaction	(10,385)	281,669	0
CO2 capital expenditures	(93,744)	(131,043)	(84,789)
Pipelines and plants capital expenditures	(184,286)	(330,417)	(236,133)
Purchases of other assets	(65,987)	(25,765)	(28,838)
Net proceeds from sales of oil and natural gas properties and equipment	8,037	34,750	69,370
Net proceeds from sale of short-term investments	0	83,545	0
Other	(19,480)	(10,883)	(8,147)
Net cash used for investing activities	(1,275,309)	(1,376,841)	(1,605,958)
Cash flow provided by (used for) financing activities
Bank repayments	(1,550,000)	(1,555,000)	(330,000)
Bank borrowings	1,190,000	1,870,000	715,000
Repayment of senior subordinated notes	(651,270)	0	(525,000)
Premium paid on repayment of senior subordinated notes	(36,475)	0	(13,137)
Net proceeds from issuance of senior subordinated notes	1,200,000	0	400,000
Costs of debt financing	(20,161)	(34)	(13,123)
Common stock repurchase program	(281,958)	(251,480)	(195,227)
Other	(22,346)	(17,718)	(545)
Net cash provided by (used for) financing activities	(172,210)	45,768	37,968
Net increase (decrease) in cash and cash equivalents	(86,324)	79,818	(363,176)
Cash and cash equivalents at beginning of year	98,511	18,693	381,869
Cash and cash equivalents at end of year	$ 12,187	$ 98,511	$ 18,693