Related Party Transactions (Details) - Schedule of related party transactions activity (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 investment_companies	Dec. 31, 2011 investment_companies	Dec. 31, 2010
Related Party Transaction [Line Items]
Reported net premiums written	$ 6,281,453	$ 5,795,750	$ 5,381,663
Net losses and loss expenses incurred	3,765,482	4,078,391	3,211,800
Reported acquisition costs	913,492	826,411	788,258
Number of investment management companies	4	3
Other strategic affiliates or subsidiaries
Related Party Transaction [Line Items]
Reported net premiums written	61,146	66,489	71,077
Net losses and loss expenses incurred	37,664	34,720	33,098
Reported acquisition costs	$ 24,014	$ 25,635	$ 32,790