Oil and Gas Exploration and Production Industries Disclosures, Costs Incurred (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Acquisition Costs of Properties - Proved	$ 739,000	$ 4,247,000	$ 0
Acquisition Costs of Properties - Unproved	505,303,000	300,772,000	417,358,000
Exploration Costs	445,598,000	363,554,000	603,153,000
Development Costs	6,116,550,000	5,930,591,000	4,437,994,000
Total	7,068,190,000	6,599,164,000	5,458,505,000
United States [Member]
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Acquisition Costs of Properties - Proved	739,000	4,219,000	0
Acquisition Costs of Properties - Unproved	471,345,000	295,160,000	403,509,000
Exploration Costs	333,534,000	311,369,000	454,379,000
Development Costs	5,657,378,000	5,410,378,000	3,892,403,000
Total	6,462,996,000	6,021,126,000	4,750,291,000
Asset Retirement Costs Included In Development	80,000,000	52,000,000	71,000,000
Canada [Member]
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Acquisition Costs of Properties - Proved	0	28,000	0
Acquisition Costs of Properties - Unproved	33,561,000	6,216,000	13,956,000
Exploration Costs	38,530,000	31,472,000	38,604,000
Development Costs	278,995,000	302,564,000	417,176,000
Total	351,086,000	340,280,000	469,736,000
Asset Retirement Costs Included In Development	33,000,000	70,000,000	2,000,000
Trinidad [Member]
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Acquisition Costs of Properties - Proved	0	0	0
Acquisition Costs of Properties - Unproved	1,000,000	0	0
Exploration Costs	19,555,000	2,549,000	23,386,000
Development Costs	32,609,000	138,905,000	114,986,000
Total	53,164,000	141,454,000	138,372,000
Asset Retirement Costs Included In Development	2,000,000	7,000,000	(3,000,000)
Other International [Member]
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Acquisition Costs of Properties - Proved	0	0	0
Acquisition Costs of Properties - Unproved	(603,000)	(604,000)	(107,000)
Exploration Costs	53,979,000	18,164,000	86,784,000
Development Costs	147,568,000	78,744,000	13,429,000
Total	200,944,000	96,304,000	100,106,000
Asset Retirement Costs Included In Development	$ 12,000,000	$ 4,000,000	$ 2,000,000