Reserve For Losses, LAE And Future Policy Benefit Reserve (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Prior years' reserves	$ 12,258	$ 14,767	$ 62,846
Increase (decrease) in insurance business and non-US reinsurance business	29,612	71,896	29,884
Increase (decrease) in insurance and reinsurance business	17,354	(57,129)	32,962
Reinsurance receivable, affiliated and unaffiliated, total	3,627,253	3,471,302
Reinsurance receivable	2,976,992	2,901,174
Retrocession percent	5.00%
Contracts of insurance and reinsurance received clamis during the past three years, in years	20 years
Case reserves reported by ceding companies	138,449
Additional case reserves established by the Company on assumed reinsurance claims	90,637
Case reserve established by the Company on direct excess insurance claims	36,667
IBNR reserves	177,068
Gross asbestos loss reserves	422,849
Gross asbestos loss reserves, percent	95.50%
Assumed business	339,654
Direct business	83,195
Bermuda Re [Member]
Reinsurance receivable	2,881,060
Reinsurance receivable percent	79.40%
C. V. Starr [Member]
Reinsurance receivable	$ 181,535
Reinsurance receivable percent	5.00%