Financial Guaranty Insurance Contracts (Details 12) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	$ 122,000,000	$ 140,800,000	$ 372,000,000	$ 166,000,000
Effect of consolidating FG VIEs	500,000	(16,900,000)	(2,700,000)	(67,600,000)
Loss and loss adjustment expenses	122,446,000	123,913,000	369,293,000	98,333,000
Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	128,000,000	140,800,000	378,000,000	166,000,000
Financial Guaranty | U.S. RMBS
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	69,600,000	125,600,000	143,300,000	146,300,000
Financial Guaranty | Total first lien
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	63,100,000	95,100,000	122,500,000	64,700,000
Financial Guaranty | Prime first lien
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	500,000	1,200,000	900,000	1,100,000
Financial Guaranty | Alt-A first lien
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	29,000,000	19,200,000	27,700,000	27,400,000
Financial Guaranty | Option ARM
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	16,900,000	70,400,000	69,400,000	41,300,000
Financial Guaranty | Subprime
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	16,700,000	4,300,000	24,500,000	(5,100,000)
Financial Guaranty | Second lien
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	6,500,000	30,500,000	20,800,000	81,600,000
Financial Guaranty | CES
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	2,400,000	(5,700,000)	1,600,000	(15,600,000)
Financial Guaranty | HELOCs
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	4,100,000	36,200,000	19,200,000	97,200,000
Financial Guaranty | TruPS [Member]
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	(1,800,000)	3,700,000	(6,100,000)	3,700,000
Financial Guaranty | Structured finance
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	29,300,000	7,400,000	1,200,000	27,700,000
Financial Guaranty | US Public Finance [Member]
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	25,300,000	3,400,000	44,500,000	(12,400,000)
Financial Guaranty | Public finance Non-U.S.
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	5,600,000	700,000	195,100,000	700,000
Other
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	$ (6,000,000)		$ (6,000,000)