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v3.21.1

Note 1 - Business Overview and Recent Developments (Details) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2021 USD ($) segment | Dec. 31, 2020 USD ($)
Business Overview [Abstract] |  |
Number of Reportable Business Segments | segment | 2 |
Mortgage segment |  |
Mortgage Insurance [Abstract] |  |
Private Mortgage Insurance Protects Lenders For Loans Made With Less Than This Maximum Down Payment Percentage | 20.00% |
Private Mortgage Insurance Protects Lenders For Refinancings Made to Home Buyers With Less Than This Maximum Equity-Ownership Percentage | 20.00% |
Direct Primary Mortgage Insurance in Force | $ 238,900.0 | $ 246,100.0
Direct Primary Mortgage Insurance RIF | 58,500.0 | 60,700.0
Credit Risk Transfer Transactions | Mortgage segment |  |
Mortgage Insurance [Abstract] |  |
Direct Primary Mortgage Insurance RIF | $ 428.8 | $ 392.0

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- Definition Business Overview [Abstract] + References No definition available. + Details
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Namespace Prefix: | rdn_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Mortgage Insurance [Abstract] + References No definition available. + Details
Name: | rdn_MortgageInsuranceAbstract
Namespace Prefix: | rdn_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition This element represents the maximum down payment percentage on a home's purchase price that is used to measure the need for private mortgage insurance. + References No definition available. + Details
Name: | rdn_PrivateMortgageInsuranceProtectsLendersForLoansMadeWithLessThanThisMaximumDownPaymentPercentage
Namespace Prefix: | rdn_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition This element represents the maximum equity-ownership percentage on a home's value that is used to measure the need for private mortgage insurance for refinancings. + References No definition available. + Details
Name: | rdn_PrivateMortgageInsuranceProtectsLendersForRefinancingsMadetoHomeBuyersWithLessThanThisMaximumEquityOwnershipPercentage
Namespace Prefix: | rdn_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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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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- Definition Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 18 -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8672-108599 + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
Period Type: | duration

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- Definition Amount of participating insurance in force. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 50 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6483535&loc=d3e16392-158451 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |