Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Operating activities
Net income (loss)	$ 775,620	$ 493,707	$ 84,822
Adjustments to reconcile net income (loss) to net cash flows provided by operating activities:
Non-cash interest and operating expenses	19,943	24,352	16,250
Net amortization of premium on fixed maturity securities	18,256	46,338	21,997
Provision (benefit) for deferred income taxes	385,746	80,750	(185,143)
Net realized investment losses (gains)	17,992	1,994	32,662
Net unrealized losses (gains) on credit derivatives	(553,779)	155,106	337,810
Fair value loss (gain) on committed capital securities	(35,130)	(9,195)	122,940
Goodwill and settlements of pre-existing relationship			23,341
Non-cash items in other income	5,310	4,314	(20,691)
Change in deferred acquisition costs	11,863	2,156	31,646
Change in premiums receivable, net of ceding commissions	138,479	376,478	119,663
Change in ceded unearned premium reserves	102,030	256,257	203,063
Change in unearned premium reserve	(997,973)	(1,278,206)	(731,114)
Change in loss and loss adjustment expense reserve, net	635,788	(470,839)	1,186
Change in current income taxes	(181,629)	(87,165)	175,873
Other changes in credit derivatives assets and liabilities, net	(5,050)	33,652	15,802
Change in financial guaranty variable interest entities' assets and liabilities, net	352,226	540,691
Other	(14,073)	(41,201)	29,063
Net cash flows provided by (used in) operating activities	675,619	129,189	279,170
Fixed maturity securities:
Purchases	(2,308,078)	(2,461,692)	(2,287,668)
Sales	1,107,473	1,063,581	1,519,300
Maturities	662,970	994,360	217,895
Net sales (purchases) of short-term investments	319,992	613,267	(397,100)
Net proceeds from paydowns on financial guaranty variable interest entities' assets	760,374	423,997
Cash paid to acquire Assured Guaranty Municipal Holdings Inc., net of cash acquired			(458,998)
Other	18,618	19,786	9,350
Net cash flows provided by (used in) investing activities	561,349	653,299	(1,397,221)
Financing activities
Net proceeds from issuance of common stock			1,022,096
Net proceeds from issuance of equity units			167,972
Dividends paid	(33,035)	(33,190)	(22,332)
Repurchases of common stock	(23,311)	(10,457)	(3,676)
Share activity under option and incentive plans	(1,192)	(2,062)	(667)
Tax benefit for stock options exercised		28	(16)
Net paydowns of financial guaranty variable interest entities' liabilities	(1,053,280)	(650,862)
Repayment of long-term debt	(22,137)	(20,891)	(14,823)
Net cash flows provided by (used in) financing activities	(1,132,955)	(717,434)	1,148,554
Effect of exchange rate changes	2,142	(798)	1,325
Increase in cash	106,155	64,256	31,828
Cash at beginning of year	108,389	44,133	12,305
Cash at end of year	214,544	108,389	44,133
Cash paid (received) during the period for:
Income taxes	33,537	39,215	27,849
Interest	$ 91,599	$ 92,190	$ 56,418