Note 11 - Losses and Loss Adjustment Expense - Reserve Activity (Details)	Mar. 31, 2021	Mar. 31, 2020
Primary Mortgage Product \| Mortgage segment
Default To Claim Rate Estimate, Gross, For New Defaults	8.00%	7.50%

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:	num:percentItemType
Balance Type:	na
Period Type:	instant