Financial Derivatives (Schedule Of Gains And Losses On Derivative Contracts) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Derivative [Line Items]
Net Realized Gain/(Loss)	$ (34,797)	$ 16,307	$ 2,072
Change in Net Unrealized Gain/(Loss)	13,417	(21,878)	(15,004)
Financial Derivatives - Assets [Member]
Derivative [Line Items]
Net Realized Gain/(Loss)	(17,464)	12,817	1,566
Change in Net Unrealized Gain/(Loss)	(2,201)	(7,786)	(17,693)
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)	(1,164)	9,969	11,415
Change in Net Unrealized Gain/(Loss)	3,218	(5,721)	(20,085)
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)	(14,870)	3,751	(7,904)
Change in Net Unrealized Gain/(Loss)	(5,887)	192	3,613
Financial Derivatives - Assets [Member] | Credit Default Swaps On Corporate Bond Indices [Member]
Derivative [Line Items]
Primary risk exposure	Credit	Credit
Net Realized Gain/(Loss)	(1,548)	(709)
Change in Net Unrealized Gain/(Loss)	570	(570)
Financial Derivatives - Assets [Member] | Credit Default Swaps On Corporate Bond [Member]
Derivative [Line Items]
Primary risk exposure			Credit
Net Realized Gain/(Loss)			(2,281)
Change in Net Unrealized Gain/(Loss)			(2,650)
Financial Derivatives - Assets [Member] | Other Swaps [Member]
Derivative [Line Items]
Primary risk exposure			Interest Rates
Net Realized Gain/(Loss)			335
Change in Net Unrealized Gain/(Loss)			(257)
Financial Derivatives - Assets [Member] | Interest Rate Swaps [Member]
Derivative [Line Items]
Primary risk exposure	Interest Rates	Interest Rates	Interest Rates
Net Realized Gain/(Loss)	169	(195)	1
Change in Net Unrealized Gain/(Loss)	(91)	(1,699)	1,686
Financial Derivatives - Assets [Member] | Eurodollar Futures [Member]
Derivative [Line Items]
Primary risk exposure	Interest Rates	Interest Rates
Net Realized Gain/(Loss)	(51)	1
Change in Net Unrealized Gain/(Loss)	(11)	12
Financial Derivatives - Liabilities [Member]
Derivative [Line Items]
Net Realized Gain/(Loss)	(17,333)	3,490	506
Change in Net Unrealized Gain/(Loss)	15,618	(14,092)	2,689
Financial Derivatives - Liabilities [Member] | Credit Default Swaps On Asset Backed Securities [Member]
Derivative [Line Items]
Primary risk exposure	Credit		Credit
Net Realized Gain/(Loss)	(79)		(1,657)
Change in Net Unrealized Gain/(Loss)	(1)		3,881
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)	9,665	14,319	9,324
Change in Net Unrealized Gain/(Loss)	(491)	474	(572)
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)	(579)	(297)	(1,101)
Change in Net Unrealized Gain/(Loss)	(122)	359	787
Financial Derivatives - Liabilities [Member] | Total Return Swaps [Member]
Derivative [Line Items]
Primary risk exposure	Equity Market	Equity Market	Equity Market
Net Realized Gain/(Loss)	(3,563)	(1,599)	(854)
Change in Net Unrealized Gain/(Loss)	209	(274)	88
Financial Derivatives - Liabilities [Member] | Interest Rate Swaps [Member]
Derivative [Line Items]
Primary risk exposure	Interest Rates	Interest Rates	Interest Rates
Net Realized Gain/(Loss)	(22,777)	(7,839)	(1,517)
Change in Net Unrealized Gain/(Loss)	16,094	(15,541)	(1,677)
Financial Derivatives - Liabilities [Member] | Eurodollar Futures [Member]
Derivative [Line Items]
Primary risk exposure	Interest Rates	Interest Rates	Interest Rates
Net Realized Gain/(Loss)	0	(1,094)	(3,689)
Change in Net Unrealized Gain/(Loss)	$ (71)	$ 890	$ 182