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Losses and LAE - Additional Information (Details) - Primary Mortgage Product - Mortgage Insurance revenues - Default	9 Months Ended
	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%

X

- Definition

This concept represents the rate at which newly reported defaulted loans are expected to result in a claim.

+ References

No definition available.

+ Details

Name:	rdn_DefaultToClaimRateEstimateGrossForNewDefaults
Namespace Prefix:	rdn_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

X

- 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

X

- 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

X

- 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

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

X

- Details

Name:	srt_ProductOrServiceAxis=rdn_PrimaryMortgageProductMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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