Note 8 - Reinsurance - QSR Program (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
QSR Program \| Radian Guaranty
RIF Ceded	$ 381.8	$ 644.5

First Lien Primary Mortgage Insurance Risk In Force Ceded

No definition available.

Name:	rdn_FirstLienPrimaryMortgageInsuranceRiskInForceCeded
Namespace Prefix:	rdn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant