Financial Guaranty Insurance Contracts (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Effect of Retrospective Application of New Deferred Acquisition Cost Guidance
Deferred acquisition costs	$ 129,015		$ 132,418
Retained earnings	1,208,380		1,707,922
Amortization of deferred acquisition costs	5,413	3,662	0
Other operating expenses	61,280	62,883
Total expenses	338,213	65,725	0
Income (loss) before provision for income taxes	(695,619)	213,188
Total provision (benefit) for income taxes	(212,595)	73,932
Net income (loss)	(483,024)	139,256	0
Earnings per share:
Basic (in dollars per share)	$ (2.65)	$ 0.76	$ 0.00
Diluted (in dollars per share)	$ (2.65)	$ 0.74	$ 0.00
As Reported
Effect of Retrospective Application of New Deferred Acquisition Cost Guidance
Amortization of deferred acquisition costs		7,400
Other operating expenses		56,800
Total expenses		63,500
Income (loss) before provision for income taxes		215,500
Total provision (benefit) for income taxes		74,900
Net income (loss)		140,600
Earnings per share:
Basic (in dollars per share)		$ 0.76
Diluted (in dollars per share)		$ 0.74
Retrospective Application of New Deferred Acquisition Cost Guidance | Retroactive Application Adjustment
Effect of Retrospective Application of New Deferred Acquisition Cost Guidance
Deferred acquisition costs			(94,400)
Retained earnings			(64,000)
Amortization of deferred acquisition costs		(3,700)
Other operating expenses		6,000
Total expenses		2,300
Income (loss) before provision for income taxes		(2,300)
Total provision (benefit) for income taxes		(1,000)
Net income (loss)		$ (1,300)
Earnings per share:
Diluted (in dollars per share)		$ (0.0001)