Note 12 - Financial Guaranty Insurance Contracts Adjustments To Premiums Earned For Financial Guaranty Contracts (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010
Adjustments To Premiums Earned For Financial Guaranty Contracts [Line Items]
Refundings	$ 27.2	$ 35.8
Recaptures/commutations	2.8	0
Adjustments to installment premiums, gross of commissions	0.4	0.4
Unearned premium acceleration upon establishment of case reserves	3.2	1.4
Adjustment To Premiums Earned Foreign Exchange Revaluation Gross of Commission	1.1	(1.4)
Policy cancellations	0	2.3
Total Adjustment To Premiums Earned For Financial Guaranty Contracts	$ 34.7	$ 38.5

Name:	rdn_AdjustmentsToPremiumsEarnedForFinancialGuarantyContractsLineItems
Namespace Prefix:	rdn_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Adjustment To Installment Premiums Gross of Commissions

+ References

No definition available.

+ Details

Name:	rdn_AdjustmentToInstallmentPremiumsGrossOfCommissions
Namespace Prefix:	rdn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Adjustment To Premiums Earned Foreign Exchange Revaluation Gross of Commission

+ References

No definition available.

+ Details

Name:	rdn_AdjustmentToPremiumsEarnedForeignExchangeRevaluationGrossOfCommission
Namespace Prefix:	rdn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Adjustment To Premiums Earned For Financial Guaranty Contracts Other

+ References

No definition available.

+ Details

Name:	rdn_AdjustmentToPremiumsEarnedForFinancialGuarantyContractsOther
Namespace Prefix:	rdn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Premiums Earned Financial Guaranty Adjustment for Recaptures

+ References

No definition available.

+ Details

Name:	rdn_PremiumsEarnedFinancialGuarantyAdjustmentForRecaptures
Namespace Prefix:	rdn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Premiums Earned For Financial Guaranty Adjustment For Refundings

+ References

No definition available.

+ Details

Name:	rdn_PremiumsEarnedForFinancialGuarantyAdjustmentForRefundings
Namespace Prefix:	rdn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Total Adjustment To Premiums Earned For Financial Guaranty Contracts

+ References

No definition available.

+ Details

Name:	rdn_TotalAdjustmentToPremiumsEarnedForFinancialGuarantyContracts
Namespace Prefix:	rdn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This element represents the amount of premium revenue on financial guarantee insurance contracts recognized during the period that was accelerated for revenue recognition purposes.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Number 163

-Paragraph 30

-Subparagraph d

-Name Statement of Financial Accounting Standard (FAS)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 605

-Section 50

-Paragraph 4

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6933581&loc=SL5749298-161291

+ Details

Name:	us-gaap_FinancialGuaranteeInsuranceContractsAcceleratedPremiumRevenueAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration