Income Taxes (Schedule Of Tax Attributes Available To Reduce Future Income Taxes) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
U.K. [Member] | Corporate Tax [Member] | Net Operating Loss Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Carry-forward Amount	610,743	638,466
U.K. [Member] | Supplemental Corporate Tax [Member] | Net Operating Loss Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Carry-forward Amount	346,828	455,318
U.S. [Member] | Corporate Tax [Member] | Minimum [Member]
Operating Loss Carryforwards [Line Items]
Years of Expiration	2023
U.S. [Member] | Corporate Tax [Member] | Maximum [Member]
Operating Loss Carryforwards [Line Items]
Years of Expiration	2034
U.S. [Member] | Corporate Tax [Member] | Net Operating Loss Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Carry-forward Amount	354,171	232,745
U.S. [Member] | Corporate Tax [Member] | Net Operating Loss Carryforward [Member] | Minimum [Member]
Operating Loss Carryforwards [Line Items]
Years of Expiration		2023
U.S. [Member] | Corporate Tax [Member] | Net Operating Loss Carryforward [Member] | Maximum [Member]
Operating Loss Carryforwards [Line Items]
Years of Expiration		2033
U.S. [Member] | State Income Tax [Member] | Minimum [Member]
Operating Loss Carryforwards [Line Items]
Years of Expiration	2015	2014
U.S. [Member] | State Income Tax [Member] | Maximum [Member]
Operating Loss Carryforwards [Line Items]
Years of Expiration	2034	2033
U.S. [Member] | State Income Tax [Member] | Net Operating Loss Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Carry-forward Amount	84,069	83,613
U.S. [Member] | Capital Gains Tax [Member] | Capital Loss Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Years of Expiration	2015	2015
Carry-forward Amount	1,848	1,848