Note 11 - Losses and LAE - Reserve Activity (Details) - Primary Mortgage Product - Mortgage segment	9 Months Ended
Sep. 30, 2021	Apr. 30, 2021
Decrease in Number of New Primary Default Notices	(70.00%)
Default To Claim Rate Estimate, Gross, For New Defaults	8.00%	8.50%

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

No definition available.

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