Related Party Transactions (Details) - Schedule of related party transactions activity (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 investment_companies	Sep. 30, 2011
Related Party Transaction [Line Items]
Reported net premiums written	$ 1,387,751	$ 1,383,475	$ 4,862,376	$ 4,585,682
Net losses and loss expenses incurred	894,076	988,059	2,574,496	3,020,508
Reported acquisition costs	236,347	207,553	679,435	611,142
Number of investment management companies			4
Reinsurance Contracts Arx Holding Corporation [Member]
Related Party Transaction [Line Items]
Reported net premiums written	27,480	22,854	53,676	45,626
Net losses and loss expenses incurred	10,730	11,318	26,553	24,580
Reported acquisition costs	$ 8,945	$ 6,743	$ 21,558	$ 17,810