Derivatives (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Derivative [Line Items]
Asset derivatives at fair value		$ 70,585
Liability derivatives at fair value		45,238
Fair value		25,347
[DesignatedAsHedgingInstrumentMember]
Derivative [Line Items]
Asset derivatives at fair value	0	0
Liability derivatives at fair value	0	1,160
Fair value	0	(1,160)
[DesignatedAsHedgingInstrumentMember] | [ForwardContractsNetInvestmentHedgeMember]
Derivative [Line Items]
Asset derivatives at fair value		0
Liability derivatives at fair value		1,160
Notional value		198,448
Fair value		(1,160)
[NondesignatedMember]
Derivative [Line Items]
Asset derivatives at fair value	31,269	70,585
Liability derivatives at fair value	32,025	44,078
Fair value	(756)	26,507
[NondesignatedMember] | [ForeignExchangeForwardMember]
Derivative [Line Items]
Asset derivatives at fair value	7,865	27,880
Liability derivatives at fair value	5,816	12,487
Notional value	2,555,230	1,770,448
Fair value	2,049	15,393
[NondesignatedMember] | [ForeignExchangeOptionMember]
Derivative [Line Items]
Asset derivatives at fair value	1,074	3,516
Liability derivatives at fair value	321	0
Notional value	110,079	104,386
Fair value	753	3,516
[NondesignatedMember] | [FutureMember]
Derivative [Line Items]
Asset derivatives at fair value	13,572	30,593
Liability derivatives at fair value	14,173	7,956
Notional value	2,534,995	1,756,811
Fair value	(601)	22,637
[NondesignatedMember] | [CreditDefaultSwapBuyingProtectionMember]
Derivative [Line Items]
Asset derivatives at fair value	92	93
Liability derivatives at fair value	1,285	2,407
Notional value	94,961	113,752
Fair value	(1,193)	(2,314)
[NondesignatedMember] | [CreditDefaultSwapSellingProtectionMember]
Derivative [Line Items]
Asset derivatives at fair value	246	533
Liability derivatives at fair value	772	401
Notional value	17,500	27,500
Fair value	(526)	132
[NondesignatedMember] | [InsuranceLinkedSecuritiesMember]
Derivative [Line Items]
Asset derivatives at fair value	0	1,320
Liability derivatives at fair value	968	1,393
Notional value	136,375	88,765
Fair value	(968)	(73)
[NondesignatedMember] | [TotalReturnSwapMember]
Derivative [Line Items]
Asset derivatives at fair value	7,673	6,041
Liability derivatives at fair value	640	12,848
Notional value	122,230	161,408
Fair value	7,033	(6,807)
[NondesignatedMember] | [InterestRateSwapMember]
Derivative [Line Items]
Asset derivatives at fair value	0	246
Liability derivatives at fair value	7,992	6,033
Notional value	0	0
Fair value	(7,992)	(5,787)
[NondesignatedMember] | [ToBeAnnouncedSecuritiesMember]
Derivative [Line Items]
Asset derivatives at fair value	747	363
Liability derivatives at fair value	58	553
Notional value	104,315	149,065
Fair value	$ 689	$ (190)