Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Investment portfolio:
Fixed maturity securities, available-for-sale, at fair value (amortized cost of $9,659,413 and $9,638,404)	$ 10,204,938	$ 10,141,850
Short term investments, at fair value	903,363	734,046
Other invested assets	203,900	222,869
Total investment portfolio	11,312,201	11,098,765
Cash	182,003	214,544
Premiums receivable, net of ceding commissions payable	1,018,672	1,002,852
Ceded unearned premium reserve	631,398	708,872
Deferred acquisition costs	129,015	132,418
Reinsurance recoverable on unpaid losses	152,898	69,300
Salvage and subrogation recoverable	367,343	367,718
Credit derivative assets	463,556	468,933
Deferred tax asset, net	1,031,805	803,529
Current income tax receivable	50,317	76,430
Financial guaranty variable interest entities' assets, at fair value	2,827,652	2,819,077
Other assets	337,953	262,222
Total assets	18,504,813	18,024,660
Liabilities and shareholders' equity
Unearned premium reserve	5,839,223	5,962,799
Loss and loss adjustment expense reserve	954,475	679,011
Reinsurance balances payable, net	204,173	170,982
Long-term debt	1,034,667	1,038,302
Credit derivative liabilities	2,416,268	1,772,803
Financial guaranty variable interest entities' liabilities with recourse, at fair value	2,365,177	2,396,945
Financial guaranty variable interest entities' liabilities without recourse, at fair value	1,085,618	1,061,497
Other liabilities	422,694	290,756
Total liabilities	14,322,295	13,373,095
Commitments and contingencies (See Note 12)
Common stock ($0.01 par value, 500,000,000 shares authorized; 182,524,573 and 182,235,798 shares issued and outstanding in 2012 and 2011)	1,825	1,822
Additional paid-in capital	2,569,526	2,569,922
Retained earnings	1,208,380	1,707,922
Accumulated other comprehensive income, net of tax of $149,205 and $135,344	398,387	367,499
Deferred equity compensation (320,193 shares in 2012 and 2011)	4,400	4,400
Total shareholders' equity	4,182,518	4,651,565
Total liabilities and shareholders' equity	$ 18,504,813	$ 18,024,660