Fair Value Of Financial Instruments (Schedule Of Fair Value Measurement Using Significant Unobservable Inputs Level Three) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Other invested assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Opening balance	$ 520,890		$ 562,267		$ 540,409		$ 347,632
Realized and unrealized gains (losses) included in net income	11,871		(34,729)		26,753		(22,236)
Purchases	34,800		29,553		52,578		274,893
Sales	(2,859)		(5,017)		(55,038)		(48,215)
Transfers into Level 3 from Level 2	0		0		0		0
Transfers out of Level 3 to Level 2	0	[1]	0	[1]	0	[1]	0	[1]
Ending balance	564,702		552,074		564,702		552,074
Mortgage-Backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Opening balance	157,959		216,660		249,204		172,558
Realized and unrealized gains (losses) included in net income	4,855		1,876		10,951		5,103
Purchases	40,481		46,077		50,302		108,681
Sales	(48,728)		(7,021)		(124,940)		(50,308)
Transfers into Level 3 from Level 2	14,730		18,170		18,461		104,255
Transfers out of Level 3 to Level 2	(27)	[1]	(28,299)	[1]	(34,708)	[1]	(92,826)	[1]
Ending balance	169,270		247,463		169,270		247,463
Asset-Backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Opening balance	117,586		113,310		94,745		48,707
Realized and unrealized gains (losses) included in net income	988		(1,374)		1,643		(788)
Purchases	7,466		328		32,573		115,745
Sales	(7,326)		(5,708)		(57,325)		(8,933)
Transfers into Level 3 from Level 2	12,495		1,351		15,835		34,152
Transfers out of Level 3 to Level 2	(55,442)	[1]	(12,300)	[1]	(11,704)	[1]	(93,276)	[1]
Ending balance	$ 75,767		$ 95,607		$ 75,767		$ 95,607

[1] Transfers out of Level 3 are primarily attributable to the availability of market observable information.