Derivatives (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Derivative [Line Items]
Asset derivatives at fair value		$ 70,222
Liability derivatives at fair value		(44,685)
Fair value		25,537
Designated as hedging instrument [Member]
Derivative [Line Items]
Asset derivatives at fair value		0
Liability derivatives at fair value		(1,160)
Fair value		(1,160)
Designated as hedging instrument [Member] | Forward Contracts Net Investment Hedge [Member]
Derivative [Line Items]
Asset derivatives at fair value		0
Liability derivatives at fair value		(1,160)
Notional value		198,448
Fair value		(1,160)
Foreign exchange forward contracts [Member] | Derivates not designated as hedges [Member]
Derivative [Line Items]
Asset derivatives at fair value	11,634	27,880
Liability derivatives at fair value	(4,512)	(12,487)
Notional value	2,956,150	1,770,448
Fair value	7,122	15,393
Foreign currency option contracts [Member] | Derivates not designated as hedges [Member]
Derivative [Line Items]
Asset derivatives at fair value	2,921	3,516
Liability derivatives at fair value	(470)	0
Notional value	163,304	104,386
Fair value	2,451	3,516
Futures contracts [Member] | Derivates not designated as hedges [Member]
Derivative [Line Items]
Asset derivatives at fair value	6,398	30,593
Liability derivatives at fair value	(19,613)	(7,956)
Notional value	2,334,365	1,756,811
Fair value	(13,215)	22,637
Credit default swaps (protection purchased) [Member] | Derivates not designated as hedges [Member]
Derivative [Line Items]
Asset derivatives at fair value	4	93
Liability derivatives at fair value	(2,162)	(2,407)
Notional value	109,890	113,752
Fair value	(2,158)	(2,314)
Credit default swaps (assumed risks) [Member] | Derivates not designated as hedges [Member]
Derivative [Line Items]
Asset derivatives at fair value	906	533
Liability derivatives at fair value	0	(401)
Notional value	27,500	27,500
Fair value	906	132
Insurance-linked securities [Member] | Derivates not designated as hedges [Member]
Derivative [Line Items]
Asset derivatives at fair value	274	1,320
Liability derivatives at fair value	(15,126)	(1,393)
Notional value	95,848	88,765
Fair value	(14,852)	(73)
Total return swaps [Member] | Derivates not designated as hedges [Member]
Derivative [Line Items]
Asset derivatives at fair value	4,685	6,041
Liability derivatives at fair value	(11,459)	(12,848)
Notional value	159,720	161,408
Fair value	(6,774)	(6,807)
Interest rate swaps [Member] | Derivates not designated as hedges [Member]
Derivative [Line Items]
Asset derivatives at fair value	52	246
Liability derivatives at fair value	(5,203)	(6,033)
Notional value	0	0
Fair value	(5,151)	(5,787)
Derivates not designated as hedges [Member]
Derivative [Line Items]
Asset derivatives at fair value	26,874	70,222
Liability derivatives at fair value	(58,545)	(43,525)
Fair value	$ (31,671)	$ 26,697