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v3.25.3

Losses and LAE - Additional Information (Details) - Primary Mortgage Product - Mortgage Insurance revenues - Default | 9 Months Ended
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Sep. 30, 2025 | Sep. 30, 2024
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
New primary defaults | 37,350 | 36,568
Increase (decrease) in number of new primary default notices (in percent) | 2.00% |
Default to claim rate estimate, gross, for new defaults | 7.50% | 8.00%

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- Definition This concept represents the rate at which newly reported defaulted loans are expected to result in a claim. + References No definition available. + Details
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Namespace Prefix: | rdn_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition New Primary Defaults + References No definition available. + Details
Name: | rdn_NewPrimaryDefaults
Namespace Prefix: | rdn_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Definition Percentage Change in Number of New Primary Default Notices + References No definition available. + Details
Name: | rdn_PercentageChangeInNumberOfNewPrimaryDefaultNotices
Namespace Prefix: | rdn_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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

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- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=rdn_MortgageInsuranceSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |