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Note 15 - Share-Based and Other Compensation Plans (Unrecognized Compensation Expense) (Details) (Equity Compensation Plans [Member], USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Unrecognized compensation expense related to unvested portion of all stock-based awards $ 17.5us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized $ 31.9us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized $ 22.4us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
Unrecognized compensation expense weighted average recognition period (in years) 2 years    
Pro Forma [Member]
      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Unrecognized compensation expense related to unvested portion of all stock-based awards $ 17.5us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_PlanNameAxis
= rdn_EquityCompensationPlansMember
/ us-gaap_StatementScenarioAxis
= us-gaap_ProFormaMember