Related Party Transactions (Details) - Schedule of related party transactions activity (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 investment_companies	Jun. 30, 2011
Related Party Transaction [Line Items]
Reported net premiums written	$ 1,432,901	$ 1,398,253	$ 3,474,625	$ 3,202,207
Net losses and loss expenses incurred	826,355	823,584	1,680,420	2,032,449
Reported acquisition costs	218,937	215,099	443,088	403,589
Number of investment management companies			4
Reinsurance Contracts Arx Holding Corporation [Member]
Related Party Transaction [Line Items]
Reported net premiums written	10,549	8,713	26,196	22,772
Net losses and loss expenses incurred	7,862	5,570	15,823	13,261
Reported acquisition costs	$ 6,136	$ 5,218	$ 12,613	$ 11,067