Derivatives (Details) ([NondesignatedMember], USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Derivative [Line Items]
Asset derivatives at fair value	$ 18,518		$ 31,269
Liability derivatives at fair value	30,502		32,025
Fair value net	(11,984)		(756)
[ForeignExchangeForwardMember]
Derivative [Line Items]
Asset derivatives at fair value	7,889		7,865
Liability derivatives at fair value	17,395		5,816
Net notional exposure	2,170,914		2,555,230
Fair value net	(9,506)		2,049
[ForeignExchangeOptionMember]
Derivative [Line Items]
Asset derivatives at fair value	1,410		1,074
Liability derivatives at fair value	186		321
Net notional exposure	133,377		110,079
Fair value net	1,224		753
[FutureMember]
Derivative [Line Items]
Asset derivatives at fair value	1,956		13,572
Liability derivatives at fair value	1,352		14,173
Net notional exposure	3,981,107		2,534,995
Fair value net	604		(601)
[CreditDefaultSwapBuyingProtectionMember]
Derivative [Line Items]
Asset derivatives at fair value	6		92
Liability derivatives at fair value	807		1,285
Net notional exposure	55,000		94,961
Fair value net	(801)		(1,193)
[CreditDefaultSwapSellingProtectionMember]
Derivative [Line Items]
Asset derivatives at fair value	512		246
Liability derivatives at fair value	0		772
Net notional exposure	17,500		17,500
Fair value net	512		(526)
[InsuranceLinkedSecuritiesMember]
Derivative [Line Items]
Asset derivatives at fair value	0	[1]	0	[1]
Liability derivatives at fair value	2,173	[1]	968	[1]
Net notional exposure	135,964	[1]	136,375	[1]
Fair value net	(2,173)	[1]	(968)	[1]
[TotalReturnSwapMember]
Derivative [Line Items]
Asset derivatives at fair value	6,630		7,673
Liability derivatives at fair value	546		640
Net notional exposure	68,730		122,230
Fair value net	6,084		7,033
[InterestRateSwapMember]
Derivative [Line Items]
Asset derivatives at fair value	0	[2]	0	[2]
Liability derivatives at fair value	7,880	[2]	7,992	[2]
Net notional exposure	0	[2]	0	[2]
Fair value net	(7,880)	[2]	(7,992)	[2]
[ToBeAnnouncedSecuritiesMember]
Derivative [Line Items]
Asset derivatives at fair value	115		747
Liability derivatives at fair value	163		58
Net notional exposure	155,760		104,315
Fair value net	$ (48)		$ 689

[1] At December 31, 2012 and December 31, 2011, 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.

[2] (2) 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.