Note 4 - Fair Value of Financial Instruments Impact of Non-Performance Risk on Fair Value Disclosure (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2011 years		Dec. 31, 2010		Sep. 30, 2010	Dec. 31, 2009
Fair Value Concentration of Risk Disclosure Items [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	$ 168.6		$ 697.4
Fair Value, Concentration of Risk, Market Risk Management, Additional Details [Member]
Fair Value Concentration of Risk Disclosure Items [Line Items]
Corporate CDOs	9.1		105.6
Non Corporate CDO Related	194.7	[1]	762.1	[1]
NIMs related	26.3	[2]	129.3	[2]
Derivative Assets (Liabilities), at Fair Value, Net	230.1		997.0
Number Of Years In Which The Market Believes Radian Group Will Default	5
Five Year CDS Spread Details [Abstract]
Radian Group's five year CDS Spread (in basis points)	2,238		465		625	1,530
Number of Years for CDS Spread Related to Non Performance Risk In Fair Value Disclosure	5
Fair Value, Concentration of Risk, Market Risk Management, Additional Details [Member] | Fair Value Liability before Consideration of Radian Non Performance Risk
Fair Value Concentration of Risk Disclosure Items [Line Items]
Corporate CDOs	678.8		387.1
Non Corporate CDO Related	1,632.6	[1]	1,696.2	[1]
NIMs related	37.0	[2]	134.1	[2]
Derivative Assets (Liabilities), at Fair Value, Net	2,348.4		2,217.4
Fair Value, Concentration of Risk, Market Risk Management, Additional Details [Member] | Impact of Radian Non Performance Risk
Fair Value Concentration of Risk Disclosure Items [Line Items]
Corporate CDOs	(669.7)		(281.5)
Non Corporate CDO Related	(1,437.9)	[1]	(934.1)	[1]
NIMs related	(10.7)	[2]	(4.8)	[2]
Derivative Assets (Liabilities), at Fair Value, Net	(2,118.3)		(1,220.4)
Market View Of The Probability That Radian Group Will Default In The Next Five Years	79.00%		32.00%
Change in Impact of Non Performance Risk on Fair Value of Financial Instruments	$ 897.9

[1] Includes the net liability recorded within derivative assets and derivative liabilities, and the net liability recorded within VIE debt and other financial statement line items for consolidated VIEs.

[2] Includes NIMS VIE debt and NIMS derivative assets.