Exploratory Well Costs (Details) (USD $)	6 Months Ended
	Jun. 30, 2012
Exploratory Well Costs [Abstract]
Balance at December 31, 2011	$ 61,111,000
Additions Pending the Determination of Proved Reserves	60,885,000
Reclassifications to Proved Properties	(23,572,000)
Charged to Dry Hole Costs	(9,671,000)
Foreign Currency Translations	266,000
Balance at June 30, 2012	89,019,000
Capitalized exploratory well costs that have been capitalized for a period less than one year	63,017,000
Capitalized exploratory well costs that have been capitalized for a period greater than one year	26,002,000
Number of exploratory wells that have been capitalized for a period greater than one year	2
Number of exploratory wells related to an outside operated, offshore Central North Sea project in the United Kingdom	1
Number of exploratory wells related to a shale project in British Columbia, Canada	1
Exploratory well costs related to an outside operated, offshore Central North Sea project in the United Kingdom	20,000,000
Exploratory well costs related to a shale project in British Columbia, Canada	$ 6,000,000