Note 10 - Losses and Loss Adjustment Expense Reserve Activity (Details)	Sep. 30, 2019	Sep. 30, 2018
Primary Mortgage Product \| Mortgage Insurance Segment
Default To Claim Rate Estimate, Gross, For New Defaults	7.50%	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:	num:percentItemType
Balance Type:	na
Period Type:	instant