Reinsurance and Other Monoline Exposures (Details) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Reinsurance and Other Monoline Exposures [abstract]
Reduction to net income if unearned assumed premiums are recaptured	$ 800,000				$ 800,000
Reduction to net income if additional unearned assumed premiums are recaptured	10,100,000				10,100,000
Commutation gains (losses)			8,100,000		83,300,000		32,200,000
Commutations of Ceded Reinsurance Contracts
Increase in net unearned premium reserve	0		(22,400,000)		106,100,000		(20,100,000)
Increase in net par outstanding	0		(1,045,000,000)		19,073,000,000		(780,000,000)
Premiums Written:
Direct	45,000,000		26,900,000		106,900,000		57,400,000
Assumed	(14,300,000)	[1]	(9,900,000)	[1]	12,200,000	[1]	(51,900,000)	[1]
Ceded	800,000	[2]	400,000	[2]	87,800,000	[2]	4,400,000	[2]
Net	31,500,000		17,400,000		206,900,000		9,900,000
Premiums Earned:
Direct	245,000,000		238,600,000		451,100,000		514,900,000
Assumed	12,000,000		21,000,000		26,200,000		31,000,000
Ceded	(37,700,000)		(29,600,000)		(64,300,000)		(61,900,000)
Net earned premiums	219,299,000		230,068,000		412,976,000		484,045,000
Loss and LAE:
Direct	91,800,000		129,400,000		400,500,000		136,500,000
Assumed	45,700,000		7,200,000		63,000,000		(5,800,000)
Ceded	(15,000,000)		(12,700,000)		(94,200,000)		(32,300,000)
Loss and loss adjustment expenses	$ 122,446,000		$ 123,913,000		$ 369,293,000		$ 98,333,000

[1] Negative assumed premiums written were due to changes in expected debt service schedules.

[2] Positive ceded premiums written were due to commutations and changes in expected debt service schedules.