Supplemental Oil And Gas Disclosures (Schedule Of Base Prices Used In Determining The Standardized Measure) (Details)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Oil Price Per Bbl [Member]
Average Sales Price and Production Costs Per Unit of Production [Line Items]
Base prices, Barrel	105.35	77.55	58.05
Oil Price Per Bbl [Member] | United States [Member]
Average Sales Price and Production Costs Per Unit of Production [Line Items]
Base prices, Barrel	105.35	77.55	58.05
Oil Price Per Bbl [Member] | United Kingdom [Member]
Average Sales Price and Production Costs Per Unit of Production [Line Items]
Base prices, Barrel
Natural Gas Prices Per Mcf [Member]
Average Sales Price and Production Costs Per Unit of Production [Line Items]
Base prices, Mcf	4.34	4.40	3.76
Natural Gas Prices Per Mcf [Member] | United States [Member]
Average Sales Price and Production Costs Per Unit of Production [Line Items]
Base prices, Mcf	4.34	4.40	3.72
Natural Gas Prices Per Mcf [Member] | United Kingdom [Member]
Average Sales Price and Production Costs Per Unit of Production [Line Items]
Base prices, Mcf			5.07