Note 4 - Fair Value of Financial Instruments Fair Value Measurement Inputs for Level III Assets and Liabilities (Details) (USD $)	Mar. 31, 2013		Dec. 31, 2012
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets	$ 6,429,000		$ 13,609,000
Derivative liabilities	430,898,000		266,873,000
VIE debt—at fair value	107,401,000		108,858,000
Fair Value, Inputs, Level 3
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total Level III Assets	3.70%
Total Level III Liabilities	100.00%
Fair Value, Inputs, Level 3 | Discounted Cash Flow Valuation Technique [Member] | Collateralized Debt Obligation of Commercial Mortgage Backed Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets	1,700,000	[1]	1,600,000	[1]
Derivative liabilities	97,600,000	[1]	76,300,000	[1]
Fair Value, Inputs, Level 3 | Discounted Cash Flow Valuation Technique [Member] | Collateralized Debt Obligation of Commercial Mortgage Backed Securities [Member] | Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, CDS Spread Percent	1.30%	[2]	8.00%	[2]
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, Correlation Factor Related to Vintage and Credit Rating	72.00%		72.00%
Fair Value, Inputs, Level 3 | Discounted Cash Flow Valuation Technique [Member] | Collateralized Debt Obligation of Commercial Mortgage Backed Securities [Member] | Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, CDS Spread Percent	6.20%	[2]	9.10%	[2]
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, Correlation Factor Related to Vintage and Credit Rating	85.00%		85.00%
Fair Value, Inputs, Level 3 | Discounted Cash Flow Valuation Technique [Member] | TruPs Collateralized Debt Obligation [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets			1,600,000	[1]
Derivative liabilities	42,900,000	[1]	12,700,000	[1]
Fair Value, Inputs, Level 3 | Discounted Cash Flow Valuation Technique [Member] | TruPs Collateralized Debt Obligation [Member] | Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, CDS Spread Percent	1.30%	[2]	8.00%	[2]
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, Probability of Paying a Conditional Liquidity Claim	0.80%		0.80%
Fair Value, Inputs, Level 3 | Discounted Cash Flow Valuation Technique [Member] | TruPs Collateralized Debt Obligation [Member] | Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, CDS Spread Percent	6.20%	[2]	9.10%	[2]
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, Probability of Paying a Conditional Liquidity Claim	9.90%		36.70%
Fair Value, Inputs, Level 3 | Discounted Cash Flow Valuation Technique [Member] | TruPs Collateralized Debt Obligation [Member] | Weighted Average [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, Principal Recovery Percent	72.00%		65.00%
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, Principal Recovery Rate Using Distressed Pricing Scenario	62.00%		60.00%
Fair Value, Inputs, Level 3 | Discounted Cash Flow Valuation Technique [Member] | TruPs-Related VIE Liabilities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
VIE debt—at fair value	66,800,000	[1]	70,400,000	[1]
Fair Value, Inputs, Level 3 | Discounted Cash Flow Valuation Technique [Member] | TruPs-Related VIE Liabilities [Member] | Weighted Average [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, Discount Rate	12.50%		13.40%
Fair Value, Inputs, Level 3 | Discounted Cash Flow Valuation Technique [Member] | NIMS derivative assets
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets	1,600,000	[1]	1,600,000	[1]
Fair Value, Inputs, Level 3 | Discounted Cash Flow Valuation Technique [Member] | NIMS derivative assets | Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, CDS Spread Percent	1.60%	[2]	8.50%	[2]
Fair Value, Inputs, Level 3 | Discounted Cash Flow Valuation Technique [Member] | NIMS derivative assets | Weighted Average [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, NIMS Spread	43.90%		44.00%
Fair Value, Inputs, Level 3 | Discounted Cash Flow Valuation Technique [Member] | NIMS VIEs [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
VIE debt—at fair value	11,100,000	[1]	9,900,000	[1]
Fair Value, Inputs, Level 3 | Discounted Cash Flow Valuation Technique [Member] | NIMS VIEs [Member] | Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, CDS Spread Percent	1.60%	[2]	8.50%	[2]
Fair Value, Inputs, Level 3 | Discounted Cash Flow Valuation Technique [Member] | NIMS VIEs [Member] | Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, CDS Spread Percent	8.60%	[2]	10.90%	[2]
Fair Value, Inputs, Level 3 | Discounted Cash Flow Valuation Technique [Member] | NIMS VIEs [Member] | Weighted Average [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, NIMS Spread	43.60%		43.70%
Fair Value, Inputs, Level 3 | Discounted Cash Flow Valuation Technique [Member] | State and municipal obligations
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total Investments at Fair Value	19,200,000	[1]	19,000,000	[1]
Fair Value, Inputs, Level 3 | Discounted Cash Flow Valuation Technique [Member] | State and municipal obligations | Weighted Average [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, Discount Rate	8.80%		8.80%
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, Expected Loss Rate	19.00%		19.00%
Fair Value, Inputs, Level 3 | Discounted Cash Flow Valuation Technique [Member] | Other investments
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total Investments at Fair Value	76,900,000	[1]	78,000,000	[1]
Fair Value, Inputs, Level 3 | Discounted Cash Flow Valuation Technique [Member] | Other investments | Weighted Average [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, Discount Rate	2.40%		1.90%
Fair Value, Inputs, Level 3 | Base Correlation Model Valuation Technique [Member] | Corporate collateralized debt obligations (CDO's)[Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative assets	3,100,000	[1]	8,800,000	[1]
Derivative liabilities	13,000,000	[1]	6,000,000	[1]
Fair Value, Inputs, Level 3 | Base Correlation Model Valuation Technique [Member] | Corporate collateralized debt obligations (CDO's)[Member] | Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, CDS Spread Percent	1.30%	[2]	8.00%	[2]
Fair Value, Inputs, Level 3 | Base Correlation Model Valuation Technique [Member] | Corporate collateralized debt obligations (CDO's)[Member] | Minimum [Member] | Less Than [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, Average Credit Spread	0.10%		0.10%
Fair Value, Inputs, Level 3 | Base Correlation Model Valuation Technique [Member] | Corporate collateralized debt obligations (CDO's)[Member] | Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, Average Credit Spread	2.60%		2.70%
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, CDS Spread Percent	6.20%	[2]	9.10%	[2]
Fair Value, Inputs, Level 3 | Base Correlation Model Valuation Technique [Member] | Corporate collateralized debt obligations (CDO's)[Member] | Weighted Average [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, Correlation Factor	85.00%		85.00%
Fair Value, Inputs, Level 3 | Risk-Based Model Valuation Technique [Member] | Non Corporate CDOS and other derivative transactions[Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative liabilities	$ 210,400,000	[1]	$ 101,400,000	[1]
Fair Value, Inputs, Level 3 | Risk-Based Model Valuation Technique [Member] | Non Corporate CDOS and other derivative transactions[Member] | Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, CDS Spread Percent	1.30%	[2]	8.00%	[2]
Fair Value, Inputs, Level 3 | Risk-Based Model Valuation Technique [Member] | Non Corporate CDOS and other derivative transactions[Member] | Minimum [Member] | Less Than [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Derivative, Expected Remaining Life	1 year		1 year
Fair Value, Inputs, Level 3 | Risk-Based Model Valuation Technique [Member] | Non Corporate CDOS and other derivative transactions[Member] | Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value, Measurement with Unobservable Inputs, Additional Disclosure, CDS Spread Percent	6.20%	[2]	9.10%	[2]
Derivative, Expected Remaining Life	20 years		20 years

[1] Excludes certain assets and liabilities for which we do not develop quantitative unobservable inputs. The fair value estimates for these assets and liabilities are developed using third-party pricing information, generally without adjustment.

[2] Represents the range of Radian Group’s CDS spread that a typical market participant might use in the valuation analysis based on the remaining term of the investment.