Restatement of Previously Issued Financial Statements (Details) (USD $)	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2010	Dec. 31, 2009
Assets
Total investment portfolio	$ 11,262,484,000	$ 10,740,886,000
Cash	173,260,000	108,389,000	94,406,000	44,133,000
Premiums receivable, net of ceding commissions payable	987,115,000	1,167,587,000	1,322,500,000	1,399,200,000
Ceded unearned premium reserve	747,457,000	821,819,000
Deferred acquisition costs	230,983,000	239,805,000
Reinsurance recoverable on unpaid losses	47,976,000	22,255,000
Salvage and subrogation recoverable	360,161,000	1,032,369,000	824,800,000
Credit derivative assets	467,252,000	592,898,000
Deferred tax asset, net	676,198,000	1,259,125,000
Financial guaranty variable interest entities' assets, at fair value	3,005,380,000	3,657,481,000
Other assets	243,070,000	199,305,000
Total assets	18,404,995,000	19,841,919,000
Liabilities and shareholders' equity
Unearned premium reserve	6,111,822,000	6,972,894,000
Loss and loss adjustment expense reserve	670,743,000	574,369,000
Reinsurance balances payable, net	173,575,000	274,431,000
Long-term debt	1,041,653,000	1,052,936,000
Credit derivative liabilities	1,495,312,000	2,462,831,000
Current income tax payable		93,020,000
Financial guaranty variable interest entities' liabilities with recourse, at fair value	2,575,548,000	3,030,908,000
Financial guaranty variable interest entities' liabilities without recourse, at fair value	1,133,025,000	1,337,214,000
Other liabilities	436,602,000	309,862,000
Total liabilities	13,638,280,000	16,108,465,000
Commitments and contingencies
Common stock	1,822,000	1,837,000
Additional paid-in capital	2,567,668,000	2,585,423,000
Retained earnings	1,866,664,000	1,032,445,000
Accumulated other comprehensive income, net of tax provision (benefit)	327,061,000	111,749,000
Deferred equity compensation	3,500,000	2,000,000
Total shareholders' equity	4,766,715,000	3,733,454,000
Total liabilities and shareholders' equity	18,404,995,000	19,841,919,000
As Previously Filed
Assets
Total investment portfolio		10,729,900,000
Cash		107,200,000	87,400,000	44,100,000
Premiums receivable, net of ceding commissions payable		1,167,600,000
Ceded unearned premium reserve		821,800,000
Deferred acquisition costs		239,800,000
Reinsurance recoverable on unpaid losses		22,300,000
Salvage and subrogation recoverable		1,032,400,000	824,800,000
Credit derivative assets		592,900,000
Deferred tax asset, net		1,224,000,000
Financial guaranty variable interest entities' assets, at fair value		4,334,400,000
Other assets		199,200,000
Total assets		20,471,500,000
Liabilities and shareholders' equity
Unearned premium reserve		6,972,900,000
Loss and loss adjustment expense reserve		563,000,000
Reinsurance balances payable, net		274,400,000
Long-term debt		1,052,900,000
Credit derivative liabilities		2,465,500,000
Current income tax payable		93,000,000
Financial guaranty variable interest entities' liabilities with recourse, at fair value		2,927,000,000
Financial guaranty variable interest entities' liabilities without recourse, at fair value		2,014,100,000
Other liabilities		309,900,000
Total liabilities		16,672,700,000
Commitments and contingencies
Common stock		1,800,000
Additional paid-in capital		2,585,400,000
Retained earnings		1,098,900,000
Accumulated other comprehensive income, net of tax provision (benefit)		110,700,000
Deferred equity compensation		2,000,000
Total shareholders' equity		3,798,800,000
Total liabilities and shareholders' equity		20,471,500,000
FG VIE Eliminations
Assets
Total investment portfolio		11,000,000
Cash		1,200,000	7,000,000
Deferred tax asset, net		32,100,000
Total assets		44,300,000
Liabilities and shareholders' equity
Financial guaranty variable interest entities' liabilities with recourse, at fair value		103,900,000
Total liabilities		103,900,000
Commitments and contingencies
Retained earnings		(60,700,000)
Accumulated other comprehensive income, net of tax provision (benefit)		1,100,000
Total shareholders' equity		(59,600,000)
Total liabilities and shareholders' equity		44,300,000
Other Adjustments
Assets
Deferred tax asset, net		3,000,000
Financial guaranty variable interest entities' assets, at fair value		(676,900,000)
Total assets		(673,900,000)
Liabilities and shareholders' equity
Loss and loss adjustment expense reserve		11,400,000
Credit derivative liabilities		(2,700,000)
Financial guaranty variable interest entities' liabilities without recourse, at fair value		(676,900,000)
Total liabilities		(668,200,000)
Commitments and contingencies
Retained earnings		(5,700,000)
Total shareholders' equity		(5,700,000)
Total liabilities and shareholders' equity		$ (673,900,000)