Financial Guaranty Insurance Contracts (Details 12) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Loss and LAE Reported on the Consolidated Statements of Operations
Effect of consolidating FG VIEs	$ (3,200,000)	$ (50,700,000)
Total loss and LAE	246,847,000	(25,580,000)
Greek sovereign debt
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	189,300,000
Financial Guaranty
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	250,000,000	25,200,000
Financial Guaranty | U.S. RMBS
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	73,700,000	20,700,000
Financial Guaranty | Total first lien
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	59,400,000	(30,400,000)
Financial Guaranty | Prime first lien
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	400,000	(100,000)
Financial Guaranty | Alt-A first lien
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	(1,300,000)	8,200,000
Financial Guaranty | Option ARM
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	52,500,000	(29,100,000)
Financial Guaranty | Subprime
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	7,800,000	(9,400,000)
Financial Guaranty | Second lien
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	14,300,000	51,100,000
Financial Guaranty | CES
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	(800,000)	(9,900,000)
Financial Guaranty | HELOCs
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	15,100,000	61,000,000
Financial Guaranty | Structured Finance
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	(32,400,000)	20,300,000
Financial Guaranty | Public finance
Loss and LAE Reported on the Consolidated Statements of Operations
Subtotal	$ 208,700,000	$ (15,800,000)