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Note 7 - Reinsurance QSR Program (Details) - USD ($) $ in Billions | Sep. 30, 2019 | Sep. 30, 2018
--- | --- | ---
Radian Guaranty | Reinsurer Concentration Risk | QSR Program |  |
Risk In Force | $ 0.7 | $ 1.0

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- Definition Risk In Force + References No definition available. + Details
Name: | rdn_RiskInForce
Namespace Prefix: | rdn_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | dei_LegalEntityAxis=rdn_RadianGuarantyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ConcentrationRiskByTypeAxis=us-gaap_ReinsurerConcentrationRiskMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CededCreditRiskAxis=rdn_QuotaShareReinsuranceTransactionsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |