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Supplemental Oil and Gas Disclosures (Future Cash Inflows) (Details)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
United Kingdom [Member]    
Prices Used To Determine Estimate Of Future Cash Inflows Oil 98.72end_PricesUsedToDetermineEstimateOfFutureCashInflowsOil
/ us-gaap_StatementGeographicalAxis
= country_GB		 104.45end_PricesUsedToDetermineEstimateOfFutureCashInflowsOil
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= country_GB
Prices Used To Determine Estimate Of Future Cash Inflows Gas 8.10end_PricesUsedToDetermineEstimateOfFutureCashInflowsGas
/ us-gaap_StatementGeographicalAxis
= country_GB		 10.38end_PricesUsedToDetermineEstimateOfFutureCashInflowsGas
/ us-gaap_StatementGeographicalAxis
= country_GB
United States [Member]    
Prices Used To Determine Estimate Of Future Cash Inflows Oil 84.42end_PricesUsedToDetermineEstimateOfFutureCashInflowsOil
/ us-gaap_StatementGeographicalAxis
= country_US		 97.71end_PricesUsedToDetermineEstimateOfFutureCashInflowsOil
/ us-gaap_StatementGeographicalAxis
= country_US
Prices Used To Determine Estimate Of Future Cash Inflows Gas 3.40end_PricesUsedToDetermineEstimateOfFutureCashInflowsGas
/ us-gaap_StatementGeographicalAxis
= country_US		 2.94end_PricesUsedToDetermineEstimateOfFutureCashInflowsGas
/ us-gaap_StatementGeographicalAxis
= country_US