Segment Information (Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas) (Details) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Total net premiums written	$ 395,803	$ 369,795	$ 876,674	$ 803,087
United States [Member]
Total net premiums written	215,343	192,980	478,574	438,260
Bermuda [Member]
Total net premiums written	125,452	131,119	271,783	258,901
Europe [Member]
Total net premiums written	40,663	38,550	92,539	90,710
Singapore [Member]
Total net premiums written	10,331	5,912	25,567	9,603
HongKong [Member]
Total net premiums written	$ 4,014	$ 1,234	$ 8,211	$ 5,613