Financial Derivatives (Schedule Of Gains And Losses On Derivative Contracts) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative [Line Items]
Net Realized Gain/Loss on Financial Derivatives	$ (11,211)	$ (21,479)	$ (34,797)
Unrealized Gain (Loss) on Financial Derivatives	(8,272)	13,482	13,417
Financial Derivatives - Assets [Member]
Derivative [Line Items]
Net Realized Gain/Loss on Financial Derivatives	26,098	(7,876)	(17,464)
Unrealized Gain (Loss) on Financial Derivatives	9,338	26,486	(2,201)
Financial Derivatives - Assets [Member] | Credit Default Swaps On Asset Backed Securities [Member]
Derivative [Line Items]
Primary risk exposure	Credit	Credit	Credit
Net Realized Gain/Loss on Financial Derivatives	(4,596)	(2,826)	(1,164)
Unrealized Gain (Loss) on Financial Derivatives	4,547	1,070	3,218
Financial Derivatives - Assets [Member] | Credit Default Swaps On Asset Backed Indices [Member]
Derivative [Line Items]
Primary risk exposure	Credit	Credit	Credit
Net Realized Gain/Loss on Financial Derivatives	(4,662)	(5,954)	(14,870)
Unrealized Gain (Loss) on Financial Derivatives	2,059	1,082	(5,887)
Financial Derivatives - Assets [Member] | Credit Default Swaps On Corporate Bond Indices [Member]
Derivative [Line Items]
Primary risk exposure	Credit	Credit	Credit
Net Realized Gain/Loss on Financial Derivatives	1,938	626	(1,548)
Unrealized Gain (Loss) on Financial Derivatives	(2,589)	1,026	570
Financial Derivatives - Assets [Member] | Total Return Swaps [Member]
Derivative [Line Items]
Primary risk exposure	Equity Market	Equity Market
Net Realized Gain/Loss on Financial Derivatives	12,975	2,992
Unrealized Gain (Loss) on Financial Derivatives	3	4
Financial Derivatives - Assets [Member] | Interest Rate Swaps [Member]
Derivative [Line Items]
Primary risk exposure	Interest Rates	Interest Rates	Interest Rates
Net Realized Gain/Loss on Financial Derivatives	10,610	(2,829)	169
Unrealized Gain (Loss) on Financial Derivatives	5,101	23,548	(91)
Financial Derivatives - Assets [Member] | Futures [Member]
Derivative [Line Items]
Primary risk exposure	Interest Rates/Equity Market		Interest Rates
Net Realized Gain/Loss on Financial Derivatives	4,841		(51)
Unrealized Gain (Loss) on Financial Derivatives	261		(11)
Financial Derivatives - Assets [Member] | Forwards [Member]
Derivative [Line Items]
Primary risk exposure	Currency
Net Realized Gain/Loss on Financial Derivatives	3,845
Unrealized Gain (Loss) on Financial Derivatives	884
Financial Derivatives - Assets [Member] | Other Derivatives [Member]
Derivative [Line Items]
Primary risk exposure	Credit/ Interest Rates	Credit/ Interest Rates
Net Realized Gain/Loss on Financial Derivatives	1,147	115
Unrealized Gain (Loss) on Financial Derivatives	(928)	(244)
Financial Derivatives - Liabilities [Member]
Derivative [Line Items]
Net Realized Gain/Loss on Financial Derivatives	(37,309)	(13,603)	(17,333)
Unrealized Gain (Loss) on Financial Derivatives	(17,610)	(13,004)	15,618
Financial Derivatives - Liabilities [Member] | Credit Default Swaps On Asset Backed Securities [Member]
Derivative [Line Items]
Primary risk exposure	Credit	Credit	Credit
Net Realized Gain/Loss on Financial Derivatives	(78)	(78)	(79)
Unrealized Gain (Loss) on Financial Derivatives	111	(349)	(1)
Financial Derivatives - Liabilities [Member] | Credit Default Swaps On Asset Backed Indices [Member]
Derivative [Line Items]
Primary risk exposure	Credit	Credit	Credit
Net Realized Gain/Loss on Financial Derivatives	3,111	1,870	9,665
Unrealized Gain (Loss) on Financial Derivatives	(1,743)	2,869	(491)
Financial Derivatives - Liabilities [Member] | Credit Default Swaps On Corporate Bond Indices [Member]
Derivative [Line Items]
Primary risk exposure	Credit	Credit	Credit
Net Realized Gain/Loss on Financial Derivatives	(6,242)	(9,573)	(579)
Unrealized Gain (Loss) on Financial Derivatives	6,926	(9,157)	(122)
Financial Derivatives - Liabilities [Member] | Credit Default Swaps On Corporate Bonds [Member]
Derivative [Line Items]
Primary risk exposure	Credit
Net Realized Gain/Loss on Financial Derivatives	270
Unrealized Gain (Loss) on Financial Derivatives	(782)
Financial Derivatives - Liabilities [Member] | Total Return Swaps [Member]
Derivative [Line Items]
Primary risk exposure	Equity Market	Equity Market	Equity Market
Net Realized Gain/Loss on Financial Derivatives	(5,671)	(5,260)	(3,563)
Unrealized Gain (Loss) on Financial Derivatives	46	(3)	209
Financial Derivatives - Liabilities [Member] | Interest Rate Swaps [Member]
Derivative [Line Items]
Primary risk exposure	Interest Rates	Interest Rates	Interest Rates
Net Realized Gain/Loss on Financial Derivatives	(23,939)	319	(22,777)
Unrealized Gain (Loss) on Financial Derivatives	(24,318)	(3,940)	16,094
Financial Derivatives - Liabilities [Member] | Futures [Member]
Derivative [Line Items]
Primary risk exposure	Interest Rates/Equity Market	Interest Rates	Interest Rates
Net Realized Gain/Loss on Financial Derivatives	(252)	(795)	0
Unrealized Gain (Loss) on Financial Derivatives	2,291	(2,302)	(71)
Financial Derivatives - Liabilities [Member] | Forwards [Member]
Derivative [Line Items]
Primary risk exposure	Currency	Currency
Net Realized Gain/Loss on Financial Derivatives	(2,215)	0
Unrealized Gain (Loss) on Financial Derivatives	(98)	(38)
Financial Derivatives - Liabilities [Member] | Other Derivatives [Member]
Derivative [Line Items]
Primary risk exposure	Credit/ Interest Rates/Equity Market	Interest Rates/ Equity Market
Net Realized Gain/Loss on Financial Derivatives	(2,293)	(86)
Unrealized Gain (Loss) on Financial Derivatives	$ (43)	$ (84)