Segment Information (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Schedule of gross premiums written, net premiums earned and the net change in fair value of credit derivatives
Gross Premiums Written	$ (27,873)	$ (208,074)	$ (120,467)	$ (368,285)
Net Premiums Earned	103,042	99,271	197,992	191,070
Net Change in Fair Value of Credit Derivatives	(7,415)	24,287	(14,637)	15,384
United States [Member]
Schedule of gross premiums written, net premiums earned and the net change in fair value of credit derivatives
Gross Premiums Written	(31,936)	(210,913)	(124,661)	(355,179)
Net Premiums Earned	70,555	78,648	143,541	150,129
Net Change in Fair Value of Credit Derivatives	(4,816)	17,717	(8,267)	10,518
United Kingdom [Member]
Schedule of gross premiums written, net premiums earned and the net change in fair value of credit derivatives
Gross Premiums Written	5,971	18,151	12,385	10,883
Net Premiums Earned	25,551	11,853	40,592	22,786
Net Change in Fair Value of Credit Derivatives	(813)	1,535	(4,437)	853
Other International [Member]
Schedule of gross premiums written, net premiums earned and the net change in fair value of credit derivatives
Gross Premiums Written	(1,908)	(15,312)	(8,191)	(23,989)
Net Premiums Earned	6,936	8,770	13,859	18,155
Net Change in Fair Value of Credit Derivatives	$ (1,786)	$ 5,035	$ (1,933)	$ 4,013