Goodwill and Intangible Assets (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Goodwill And Intangible Assets [Line Items]
Beginning balance	$ 634,248	$ 702,802
Amortization during the period	(44,848)	(68,554)	(40,300)
Ending balance	589,400	634,248	702,802
Intangible Assets [Line Items]
Accumulated amortization	153,679	108,831
Gross intangible assets excluding goodwill	287,546	287,546
Goodwill [Line Items]
Goodwill	455,533	455,533
Finite-Lived Intangible Assets, Future Amortization Expense [Abstract]
Future Amortization Expense Year One	31,799
Future Amortization Expense Year Two	19,479
Future Amortization Expense Year Three	15,950
Future Amortization Expense Year Four	13,900
Future Amortization Expense Year Five	12,034
Definite-lived intangible assets future amortization expense	93,162
[LifeMember]
Goodwill [Line Items]
Goodwill	17,957
[NorthAmericaMember]
Goodwill [Line Items]
Goodwill	82,026
[GlobalNonUsPcMember]
Goodwill [Line Items]
Goodwill	149,895
[GlobalNonUsSpecialtyMember]
Goodwill [Line Items]
Goodwill	179,641
[CatastropheSegmentMember]
Goodwill [Line Items]
Goodwill	26,014
[GoodwillMember]
Goodwill And Intangible Assets [Line Items]
Beginning balance	455,533	455,533
Amortization during the period	0	0
Ending balance	455,533	455,533
[DefiniteLivedIntangibleAssetsMember]
Goodwill And Intangible Assets [Line Items]
Beginning balance	171,365	239,919
Amortization during the period	(44,848)	(68,554)
Ending balance	126,517	171,365
Intangible Assets [Line Items]
Definite-lived intangible assets, gross	280,196	280,196
Accumulated amortization	153,679	108,831
[DefiniteLivedIntangibleAssetsMember] | [UnpaidLossesAndLossExpensesMember]
Intangible Assets [Line Items]
Definite-lived intangible assets, gross	191,196	191,196
Accumulated amortization	72,854	44,076
[DefiniteLivedIntangibleAssetsMember] | [UnearnedPremiumsMember]
Intangible Assets [Line Items]
Definite-lived intangible assets, gross	56,300	56,300
Accumulated amortization	56,300	51,130
[DefiniteLivedIntangibleAssetsMember] | [RenewalRightsMember]
Intangible Assets [Line Items]
Definite-lived intangible assets, gross	32,700	32,700
Accumulated amortization	24,525	13,625
[IndefiniteLivedIntangibleAssetsMember]
Goodwill And Intangible Assets [Line Items]
Beginning balance	7,350	7,350
Amortization during the period	0	0
Ending balance	7,350	7,350
[IndefiniteLivedIntangibleAssetsMember] | [InsuranceLicensesMember]
Intangible Assets [Line Items]
Accumulated amortization	0	0
Indefinite lived intangible assets	$ 7,350	$ 7,350