Property And Equipment (Narrative) (Details) (USD $)	3 Months Ended
Mar. 31, 2014	Mar. 31, 2013
Oil And Gas Properties And Equipment [Line Items]
Amortization period	3 years
Transfer period	2 years
Directly related employee costs capitalized	$ 3,100,000	$ 5,100,000
Impairment of oil and gas properties		3,534,000
U.S. [Member]
Oil And Gas Properties And Equipment [Line Items]
Impairment of oil and gas properties		3,500,000
Average price per barrel, oil	98.43	92.63
Average price per barrel, gas	3.99	2.97
United Kingdom [Member]
Oil And Gas Properties And Equipment [Line Items]
Average price per barrel, oil	107.06	110.49
Average price per barrel, gas	10.57	9.71
U.K. Activities [Member]
Oil And Gas Properties And Equipment [Line Items]
Exploration and development related capitalized costs	$ 2,600,000	$ 6,200,000

- Definition

The capitalized costs incurred during the period (excluded from amortization) in identifying areas that may warrant examination and in examining specific areas that are considered to have prospects of containing oil and gas reserves, including costs of drilling exploratory wells and exploratory-type stratigraphic test wells. Exploration costs may be incurred both before acquiring the related property (sometimes referred to in part as prospecting costs) and after acquiring the property. Principal types of exploration costs, which include depreciation and applicable operating costs of support equipment and facilities and other costs of exploration activities, are: costs of topographical, geographical and geophysical studies, rights of access to properties to conduct those studies, and salaries and other expenses of geologists, geophysical crews, and others conducting those studies. Collectively, these are sometimes referred to as geological and geophysical or "G&G" costs. Exploration costs also include costs of carrying and retaining undeveloped properties, such as delay rentals, ad valorem taxes on properties, legal costs for title defense, the maintenance of land and lease records, dry hole contributions and bottom hole contributions, costs of drilling and equipping exploratory wells and costs of drilling exploratory-type stratigraphic test wells.

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