Segment Information (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Schedule of Segment Reporting Information By Segment [Abstract]
Crude Oil and Condensate	$ 3,838,284	$ 1,998,771	$ 1,089,711
Natural Gas Liquids	779,364	462,345	258,799
Natural Gas	2,240,540	2,420,099	2,050,963
Gains on Mark-to-Market Commodity Derivative Contracts	(626,053)	(61,912)	(431,757)
Gathering, Processing and Marketing	2,115,792	909,680	407,116
Gains on Asset Dispositions, Net	492,909	223,538	535,436
Other, Net	33,173	23,551	13,177
Net Operating Revenues (2)	10,126,115	6,099,896	4,786,959
Depreciation, Depletion and Amortization	2,516,381	1,941,926	1,549,188
Operating Income (Loss)	2,113,309	523,319	970,841
Interest Income	1,019	823	1,100
Other Income (Expense)	5,834	13,420	971
Net Interest Expense	210,363	129,586	100,901
Income (Loss) Before Income Taxes	1,909,799	407,976	872,011
Income Tax Provision (Benefit)	818,676	247,322	325,384
Additions to Oil and Gas Properties, Excluding Dry Hole Costs	6,241,167	5,138,126	3,125,540
Total Property, Plant and Equipment, Net	21,288,824	18,680,900	16,139,225
Total Assets	24,838,797	21,624,233	18,118,667
United States [Member]
Schedule of Segment Reporting Information By Segment [Abstract]
Crude Oil and Condensate	3,458,248	1,700,770	945,224
Natural Gas Liquids	762,730	448,647	246,821
Natural Gas	1,593,964	1,778,823	1,540,042
Gains on Mark-to-Market Commodity Derivative Contracts	626,053	61,912	431,757
Gathering, Processing and Marketing	2,115,768	909,660	407,097
Gains on Asset Dispositions, Net	475,878	196,774	535,295
Other, Net	32,329	19,886	9,693
Net Operating Revenues (2)	9,064,970	5,116,472	4,115,929
Depreciation, Depletion and Amortization	2,131,706	1,539,240	1,282,180
Operating Income (Loss)	2,252,508	787,422	896,937
Interest Income	436	152	137
Other Income (Expense)	(6,480)	(3,905)	(7,396)
Net Interest Expense	214,360	112,226	84,411
Income (Loss) Before Income Taxes	2,032,104	671,443	805,267
Income Tax Provision (Benefit)	732,362	255,945	290,473
Additions to Oil and Gas Properties, Excluding Dry Hole Costs	5,790,590	4,491,897	2,770,482
Total Property, Plant and Equipment, Net	18,711,774	15,747,808	12,769,240
Total Assets	21,313,158	17,762,533	14,108,129
Canada [Member]
Schedule of Segment Reporting Information By Segment [Abstract]
Crude Oil and Condensate	264,895	178,349	86,140
Natural Gas Liquids	16,634	13,698	11,978
Natural Gas	178,324	285,369	315,792
Gains on Mark-to-Market Commodity Derivative Contracts	0	0	0
Gathering, Processing and Marketing	0	0	0
Gains on Asset Dispositions, Net	17,033	23,112	141
Other, Net	258	(31)	(16)
Net Operating Revenues (2)	477,144	500,497	414,035
Depreciation, Depletion and Amortization	260,084	315,849	211,514
Operating Income (Loss)	(459,520)	(516,874)	(31,767)
Interest Income	342	387	612
Other Income (Expense)	(2,375)	2,067	5,212
Net Interest Expense	23,085	34,350	28,934
Income (Loss) Before Income Taxes	(484,638)	(548,770)	(54,877)
Income Tax Provision (Benefit)	(125,474)	(146,495)	(27,073)
Additions to Oil and Gas Properties, Excluding Dry Hole Costs	259,634	446,626	268,604
Total Property, Plant and Equipment, Net	1,760,066	2,189,961	2,740,473
Total Assets	2,131,949	2,598,412	2,888,949
Trinidad [Member]
Schedule of Segment Reporting Information By Segment [Abstract]
Crude Oil and Condensate	112,554	117,605	57,089
Natural Gas Liquids	0	0	0
Natural Gas	442,589	330,247	172,560
Gains on Mark-to-Market Commodity Derivative Contracts	0	0	0
Gathering, Processing and Marketing	24	20	19
Gains on Asset Dispositions, Net	(2)	3,652	0
Other, Net	586	3,696	3,500
Net Operating Revenues (2)	555,751	455,220	233,168
Depreciation, Depletion and Amortization	107,141	71,085	47,119
Operating Income (Loss)	383,992	312,128	143,993
Interest Income	101	120	146
Other Income (Expense)	18,755	14,022	4,387
Net Interest Expense	0	448	1,332
Income (Loss) Before Income Taxes	402,848	325,822	147,194
Income Tax Provision (Benefit)	204,698	140,934	57,363
Additions to Oil and Gas Properties, Excluding Dry Hole Costs	132,159	134,198	31,219
Total Property, Plant and Equipment, Net	627,794	595,970	532,989
Total Assets	1,085,664	954,391	813,901
Other International [Member]
Schedule of Segment Reporting Information By Segment [Abstract]
Crude Oil and Condensate	2,587	2,047	1,258
Natural Gas Liquids	0	0	0
Natural Gas	25,663	25,660	22,569
Gains on Mark-to-Market Commodity Derivative Contracts	0	0	0
Gathering, Processing and Marketing	0	0	0
Gains on Asset Dispositions, Net	0	0	0
Other, Net	0	0	0
Net Operating Revenues (2)	28,250	27,707	23,827
Depreciation, Depletion and Amortization	17,450	15,752	8,375
Operating Income (Loss)	(63,671)	(59,357)	(38,322)
Interest Income	140	164	205
Other Income (Expense)	(4,066)	1,236	(1,232)
Net Interest Expense	(27,082)	(17,438)	(13,776)
Income (Loss) Before Income Taxes	(40,515)	(40,519)	(25,573)
Income Tax Provision (Benefit)	7,090	(3,062)	4,621
Additions to Oil and Gas Properties, Excluding Dry Hole Costs	58,784	65,405	55,235
Total Property, Plant and Equipment, Net	189,190	147,161	96,523
Total Assets	$ 308,026	$ 308,897	$ 307,688