Note 19 - Statutory Information Principal Differences between GAAP and SAPP (Details)	12 Months Ended
Dec. 31, 2018
Differences Between GAAP Basis and SAPP Basis
Mortgage Guaranty Insurance Companies Are Required Each Year To Establish A Contingency Reserve Equal To This Percentage Of Premiums Earned In Such Year	50.00%

Mortgage Guaranty Insurance Companies Are Required Each Year To Establish A Contingency Reserve Equal To This Percentage Of Premiums Earned In Such Year

No definition available.

Name:	rdn_MortgageGuarantyInsuranceCompaniesAreRequiredEachYearToEstablishContingencyReserveEqualToThisPercentageOfPremiumsEarnedInSuchYear
Namespace Prefix:	rdn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration