Supplemental Oil And Gas Disclosures (Costs Incurred In Oil And Gas Producing Activities) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Proved properties					$ 56
Unproved properties	41		364		1,829
Total property acquisition costs	41		364		1,885
Exploration costs	2,513		1,362		39,225
Development costs	126,196	[1]	53,002	[1]	71,489	[1]
Asset retirement cost	46,446		25,356		69,112
Total costs incurred	175,196		80,084		181,711
United States [Member]
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Proved properties					56
Unproved properties	41		364		1,829
Total property acquisition costs	41		364		1,885
Exploration costs	2,513		1,362		39,225
Development costs	126,196	[1]	53,002	[1]	71,489	[1]
Asset retirement cost	26,523		18,814		66,468
Total costs incurred	155,273		73,542		179,067
United Kingdom [Member]
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Proved properties
Unproved properties
Total property acquisition costs
Exploration costs
Development costs		[1]
Asset retirement cost	19,923		6,542		2,644
Total costs incurred	$ 19,923		$ 6,542		$ 2,644

[1] Development costs include costs incurred to obtain access to proved reserves to drill and equip development wells. Development costs also include costs of developmental dry holes.