Derivatives (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Derivative [Line Items]
Derivative Fair Value Of Derivative Asset	$ 67,880	[1]	$ 18,518	[1]
Derivative Fair Value Of Derivative Liability	(18,882)	[1]	(30,502)	[1]
Fair value net	48,998		(11,984)
[ForeignExchangeForwardMember]
Derivative [Line Items]
Derivative Fair Value Of Derivative Asset	7,486		7,889
Derivative Fair Value Of Derivative Liability	(4,656)		(17,395)
Net notional exposure	1,924,401		2,170,914
Fair value net	2,830		(9,506)
[ForeignExchangeOptionMember]
Derivative [Line Items]
Derivative Fair Value Of Derivative Asset	0		1,410
Derivative Fair Value Of Derivative Liability	(3,280)		(186)
Net notional exposure	97,113		133,377
Fair value net	(3,280)		1,224
[FutureMember]
Derivative [Line Items]
Derivative Fair Value Of Derivative Asset	55,879		1,956
Derivative Fair Value Of Derivative Liability	(9)		(1,352)
Net notional exposure	5,022,813		3,981,107
Fair value net	55,870		604
[CreditDefaultSwapBuyingProtectionMember]
Derivative [Line Items]
Derivative Fair Value Of Derivative Asset	0		6
Derivative Fair Value Of Derivative Liability	(404)		(807)
Net notional exposure	34,000		55,000
Fair value net	(404)		(801)
[CreditDefaultSwapSellingProtectionMember]
Derivative [Line Items]
Derivative Fair Value Of Derivative Asset	157		512
Derivative Fair Value Of Derivative Liability	0		0
Net notional exposure	10,000		17,500
Fair value net	157		512
[InsuranceLinkedSecuritiesMember]
Derivative [Line Items]
Derivative Fair Value Of Derivative Asset	814	[2]	0	[2]
Derivative Fair Value Of Derivative Liability	(906)	[2]	(2,173)	[2]
Net notional exposure	140,744	[2]	135,964	[2]
Fair value net	(92)	[2]	(2,173)	[2]
[TotalReturnSwapMember]
Derivative [Line Items]
Derivative Fair Value Of Derivative Asset	3,328		6,630
Derivative Fair Value Of Derivative Liability	(903)		(546)
Net notional exposure	68,414		68,730
Fair value net	2,425		6,084
[InterestRateSwapMember]
Derivative [Line Items]
Derivative Fair Value Of Derivative Asset	215	[3]	0	[3]
Derivative Fair Value Of Derivative Liability	(4,919)	[3]	(7,880)	[3]
Net notional exposure	0	[3]	0	[3]
Fair value net	(4,704)	[3]	(7,880)	[3]
[ToBeAnnouncedSecuritiesMember]
Derivative [Line Items]
Derivative Fair Value Of Derivative Asset	1		115
Derivative Fair Value Of Derivative Liability	(3,805)		(163)
Net notional exposure	143,466		155,760
Fair value net	$ (3,804)		$ (48)

[1] Amounts include all derivative instruments, irrespective of whether there is a legally enforceable master netting arrangement in place.

[2] At June 30, 2013 and December 31, 2012, insurance-linked securities include a longevity swap for which the notional amount is not reflective of the overall potential exposure of the swap. As such, the Company has included the probable maximum loss under the swap within the net notional exposure as an approximation of the notional amount.

[3] The Company enters into interest rate swaps to mitigate notional exposures on certain total return swaps. Accordingly, the notional value of interest rate swaps is not presented separately in the table.