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, 2012		Dec. 31, 2011		Dec. 31, 2010
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Unproved properties			$ 41		$ 364
Total property acquisition costs			41		364
Exploration costs	135,311		2,513		1,362
Development costs	17,344	[1]	126,196	[1]	53,002	[1]
Asset retirement cost	59,715	[2]	46,446	[2]	25,356	[2]
Total costs incurred	212,370		175,196		80,084
Camelot Field [Member]
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Asset retirement cost	$ 15,500		$ 20,000		$ 900

[1] Development costs include costs incurred to obtain access to proved reserves to drill and equip development wells.

[2] Asset retirement costs include $15.5 million, $20.0 million, $0.9 million, respectively, associated with the Camelot field in the United Kingdom during the years ended December 31, 2012, 2011 and 2010.