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Note 6 - Goodwill and Other Acquired Intangible Assets, Net Accounting Policy Considerations (Details)	9 Months Ended
	Sep. 30, 2018 segment
Mortgage and Real Estate Services Segment
Goodwill [Line Items]
Number of Reporting Units	1

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_GoodwillLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Number of reporting units tested for impairment of goodwill. A reporting unit is an operating segment or one level below an operating segment.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfReportingUnits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=rdn_MortgageandRealEstateServicesSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: