Note 17 - Commitments and Contingencies Legal Proceedings (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014 plaintiff loan
Loss Reserve Information [Abstract]
Minimum Number of Pending or Threatened Matters That Could Effect Our Results	1
Internal Revenue Service (IRS) [Member]
Loss Reserve Information [Abstract]
Income Tax Examination, Amount of Claimed Income Tax Refund Being Disallowed for Tax Years 2006 and 2007	105
Minimum [Member]
Loss Contingencies [Line Items]
Number Of Home Mortgage Loans Involved In Pending Litigation	1
Loss Reserve Information [Abstract]
Loss Contingency, Number of Plaintiffs	1
REMIC Residual [Member] \| Internal Revenue Service (IRS) [Member]
Loss Contingencies [Line Items]
Income Tax Examination, Notice of Deficiency, Amounts Related to Unpaid Taxes and Penalties	157
Loss Reserve Information [Abstract]
Income Tax Examination, Estimated Interest on Notice of Deficiency Amounts	115
Income Tax Examination, Proposed State Liabilities Resulting from IRS Examination of Tax Years 2000 Through 2007	30
Insurance Claims [Member] \| Maximum [Member] \| Total Primary Insurance Mortgage Insurance Products [Member]
Loss Reserve Information [Abstract]
Loss Contingency, Legal Actions Commencement, Period	2 years
Insurance Claims [Member] \| Maximum [Member] \| Pool Insurance Mortgage Insurance Product [Member]
Loss Reserve Information [Abstract]
Loss Contingency, Legal Actions Commencement, Period	3 years

- Definition

This concept represents an amount identified in a Notice of Deficiency from the IRS related to an income tax examination where the use of a NOL carryback is being denied.

+ References

No definition available.

+ Details

Name:	rdn_IncomeTaxExaminationAmountofClaimedIncomeTaxRefundBeingDisallowedforTaxYears2006and2007
Namespace Prefix:	rdn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This concept represents the estimated interest on amounts assessed by the IRS on the Notice of Deficiency received as part of an income tax examination.

+ References

No definition available.

+ Details

Name:	rdn_IncomeTaxExaminationEstimatedInterestonNoticeofDeficiencyAmounts
Namespace Prefix:	rdn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of estimated state tax liabilities as of the balance sheet date arising from IRS examinations for tax years 2000 through 2007.

+ References

No definition available.

+ Details

Name:	rdn_IncomeTaxExaminationEstimatedStateTaxLiabilitiesResultingfromIRSExaminationofTaxYears2000Through2007
Namespace Prefix:	rdn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This concept represents the amount assessed by the IRS in the Notice of Deficiency related to unpaid taxes and penalties based on the outcome of an income tax examination.

+ References

No definition available.

+ Details

Name:	rdn_IncomeTaxExaminationNoticeofDeficiencyAmountsRelatedtoUnpaidTaxesandPenalties
Namespace Prefix:	rdn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Under Our Master Insurance Policy Any Suit Or Action Arising From Any Right Of The Insured Under The Policy Must Be Commenced Within This Number Of Years After Such Right First Arose

+ References

No definition available.

+ Details

Name:	rdn_LossContingencyLegalActionsCommencementPeriod
Namespace Prefix:	rdn_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Definition

This concept represents the minimum number of currently pending or threatened matters that could potentially impact our results.

+ References

No definition available.

+ Details

Name:	rdn_MinimumNumberofPendingorThreatenedMattersThatCouldEffectOurResults
Namespace Prefix:	rdn_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number Of Home Mortgage Loans Involved In Pending Litigation

+ References

No definition available.

+ Details

Name:	rdn_NumberOfHomeMortgageLoansInvolvedInPendingLitigation
Namespace Prefix:	rdn_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_LossContingenciesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of plaintiffs that have filed claims pertaining to a loss contingency.

+ References

No definition available.

+ Details

Name:	us-gaap_LossContingencyNumberOfPlaintiffs
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_IncomeTaxAuthorityAxis=us-gaap_InternalRevenueServiceIRSMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=us-gaap_InsuranceClaimsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ReasonablyPossibleSignificantChangeInUnrecognizedTaxBenefitsByItemAxis=rdn_REMICResidualMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: