Restatement of Previously Issued Financial Statements (Details) (USD $)	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010	Dec. 31, 2009
Assets
Total investment portfolio.	$ 11,221,900,000	$ 10,740,886,000
Cash	165,490,000	108,389,000	101,266,000	44,133,000
Premiums receivable, net of ceding commissions payable	1,059,461,000	1,167,587,000	1,311,300,000
Ceded unearned premium reserve	773,321,000	821,819,000
Deferred acquisition costs	232,311,000	239,805,000
Reinsurance recoverable on unpaid losses	26,025,000	22,255,000
Salvage and subrogation recoverable	307,147,000	1,032,369,000
Credit derivative assets	603,867,000	592,898,000
Deferred tax asset, net	1,031,438,000	1,259,125,000
Current income tax receivable	187,969,000
Financial guaranty variable interest entities' assets, at fair value	3,492,204,000	3,657,481,000
Other assets	198,692,000	199,305,000
Total assets	19,299,825,000	19,841,919,000
Liabilities and shareholders' equity
Unearned premium reserve	6,315,362,000	6,972,894,000
Loss and loss adjustment expense reserve	518,145,000	574,369,000
Reinsurance balances payable, net	175,875,000	274,431,000
Long-term debt	1,046,382,000	1,052,936,000
Credit derivative liabilities	2,791,473,000	2,462,831,000
Current income tax payable		93,020,000
Financial guaranty variable interest entities' liabilities with recourse, at fair value	2,848,897,000	3,030,908,000
Financial guaranty variable interest entities' liabilities without recourse, at fair value	1,282,463,000	1,337,214,000
Other liabilities	407,321,000	309,862,000
Total liabilities	15,385,918,000	16,108,465,000
Commitments and contingencies
Common stock	1,842,000	1,837,000
Additional paid-in capital	2,590,654,000	2,585,423,000
Retained earnings	1,113,820,000	1,032,445,000
Accumulated other comprehensive income, net of tax provision (benefit)	205,591,000	111,749,000
Deferred equity compensation	2,000,000	2,000,000
Total shareholders' equity	3,913,907,000	3,733,454,000
Total liabilities and shareholders' equity	19,299,825,000	19,841,919,000
As Previously Filed
Assets
Total investment portfolio.	11,186,700,000	10,729,900,000
Cash	159,200,000	107,200,000	97,200,000	44,100,000
Premiums receivable, net of ceding commissions payable	1,059,500,000	1,167,600,000
Ceded unearned premium reserve	773,300,000	821,800,000
Deferred acquisition costs	232,300,000	239,800,000
Reinsurance recoverable on unpaid losses	26,000,000	22,300,000
Salvage and subrogation recoverable	307,100,000	1,032,400,000
Credit derivative assets	603,900,000	592,900,000
Deferred tax asset, net	1,012,000,000	1,224,000,000
Current income tax receivable	188,000,000
Financial guaranty variable interest entities' assets, at fair value	3,492,200,000	4,334,400,000
Other assets	198,700,000	199,200,000
Total assets	19,238,900,000	20,471,500,000
Liabilities and shareholders' equity
Unearned premium reserve	6,315,400,000	6,972,900,000
Loss and loss adjustment expense reserve	518,100,000	563,000,000
Reinsurance balances payable, net	175,900,000	274,400,000
Long-term debt	1,046,400,000	1,052,900,000
Credit derivative liabilities	2,788,200,000	2,465,500,000
Current income tax payable		93,000,000
Financial guaranty variable interest entities' liabilities with recourse, at fair value	2,755,100,000	2,927,000,000
Financial guaranty variable interest entities' liabilities without recourse, at fair value	1,282,500,000	2,014,100,000
Other liabilities	407,300,000	309,900,000
Total liabilities	15,288,900,000	16,672,700,000
Commitments and contingencies
Common stock	1,800,000	1,800,000
Additional paid-in capital	2,590,700,000	2,585,400,000
Retained earnings	1,149,900,000	1,098,900,000
Accumulated other comprehensive income, net of tax provision (benefit)	205,600,000	110,700,000
Deferred equity compensation	2,000,000	2,000,000
Total shareholders' equity	3,950,000,000	3,798,800,000
Total liabilities and shareholders' equity	19,238,900,000	20,471,500,000
FG VIE Eliminations
Assets
Total investment portfolio.	35,200,000	11,000,000
Cash	6,300,000	1,200,000	4,000,000
Deferred tax asset, net	18,300,000	32,100,000
Total assets	59,800,000	44,300,000
Liabilities and shareholders' equity
Financial guaranty variable interest entities' liabilities with recourse, at fair value	93,800,000	103,900,000
Total liabilities	93,800,000	103,900,000
Commitments and contingencies
Retained earnings	(34,000,000)	(60,700,000)
Accumulated other comprehensive income, net of tax provision (benefit)		1,100,000
Total shareholders' equity	(34,000,000)	(59,600,000)
Total liabilities and shareholders' equity	59,800,000	44,300,000
Other Adjustments
Assets
Deferred tax asset, net	1,100,000	3,000,000
Financial guaranty variable interest entities' assets, at fair value		(676,900,000)
Total assets	1,100,000	(673,900,000)
Liabilities and shareholders' equity
Loss and loss adjustment expense reserve		11,400,000
Credit derivative liabilities	3,200,000	(2,700,000)
Financial guaranty variable interest entities' liabilities without recourse, at fair value		(676,900,000)
Total liabilities	3,200,000	(668,200,000)
Commitments and contingencies
Retained earnings	(2,100,000)	(5,700,000)
Total shareholders' equity	(2,100,000)	(5,700,000)
Total liabilities and shareholders' equity	$ 1,100,000	$ (673,900,000)