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	$ (3,660)	$ 3,691	$ (30,866)
Increase (decrease) in insurance business and non-US reinsurance business	(57,205)	113,833	(140,760)
Increase (decrease) in insurance and reinsurance business	53,545	(110,142)	109,894
Reinsurance receivables	659,081	580,339
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
C. V. Starr [Member]
Reinsurance receivables	181,535
Reinsurance receivable, percent	27.50%
Transatlantic Reinsurance Company [Member]
Reinsurance receivables	54,095
Reinsurance receivable, percent	8.20%
Berkley Insurance Company [Member]
Reinsurance receivables	58,024
Reinsurance receivable, percent	8.80%
XL Reinsurance America [Member]
Reinsurance receivables	65,152
Reinsurance receivable, percent	9.90%
Federal Crop Insurance Company [Member]
Reinsurance receivables	$ 79,902
Reinsurance receivable, percent	12.10%