Note 10 - Losses and Loss Adjustment Expense Mortgage Insurance Reserve Assumptions (Details) - Primary Mortgage Product - Mortgage Insurance Segment	Sep. 30, 2019	Sep. 30, 2018
Default To Claim Rate Estimate, Gross, For New Defaults	7.50%	8.50%
Default To Claim Rate Estimate, Gross, For Pre-Foreclosure Stage Defaults	65.00%
Default To Claim Estimate, Gross, For Foreclosure Stage Defaults	72.00%

This concept represents the rate at which defaulted loans that have reached the stage where the foreclosure sale has been scheduled or held are expected to result in a claim.

No definition available.

Name:	rdn_DefaultToClaimEstimateGrossForForeclosureStageDefaults
Namespace Prefix:	rdn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant