Note 4 - Fair Value of Financial Instruments Impact of Non-Performance Risk on Fair Value Disclosure (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 basispoint		Dec. 31, 2012 basispoint		Mar. 31, 2012 basispoint	Dec. 31, 2011 basispoint
Fair Value Concentration of Risk Disclosure Items [Line Items]
Derivative Liability, Fair Value, Gross Liability	822.3		808.4
Derivative Credit Risk Valuation Adjustment, Derivative Liabilities	453.5		615.6
Derivative (Asset) Liability, Fair Value, Net	368.8		192.8
Fair Value, Concentration of Risk, Market Risk Management, Additional Details [Member]
Five Year CDS Spread Details [Abstract]
Radian Group's five year CDS Spread (in basis points)	513		913		1,521	2,732
Number of Years for CDS Spread Related to Non Performance Risk In Fair Value Disclosure	5 years
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]
Market View Of The Probability That Registrant Will Default In The Next Five Years	31.80%		47.70%
Change in Impact of Non Performance Risk on Fair Value of Financial Instruments	162.1
Corporate collateralized debt obligations (CDO's)[Member]
Fair Value Concentration of Risk Disclosure Items [Line Items]
Derivative Liability, Fair Value, Gross Liability	85.3		98.8
Derivative Credit Risk Valuation Adjustment, Derivative Liabilities	75.4		101.6
Derivative (Asset) Liability, Fair Value, Net	9.9		(2.8)
Non Corporate CDOS and other derivative transactions[Member]
Fair Value Concentration of Risk Disclosure Items [Line Items]
Derivative Liability, Fair Value, Gross Liability	724.2	[1]	696.6	[1]
Derivative Credit Risk Valuation Adjustment, Derivative Liabilities	374.8	[1]	509.3	[1]
Derivative (Asset) Liability, Fair Value, Net	349.4	[1]	187.3	[1]
NIMS Related [Member]
Fair Value Concentration of Risk Disclosure Items [Line Items]
Derivative Liability, Fair Value, Gross Liability	12.8	[2]	13.0	[2]
Derivative Credit Risk Valuation Adjustment, Derivative Liabilities	3.3	[2]	4.7	[2]
Derivative (Asset) Liability, Fair Value, Net	9.5	[2]	8.3	[2]

[1] Includes the net fair value liability recorded within derivative assets and derivative liabilities, but does not include the net fair value liability of derivative assets or derivative liabilities within our consolidated VIEs, as Radian Group’s credit spread has no impact on the financial instruments in these VIEs.

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