The number of insurance certificates issued under multiple insurance policies related to the Ocwen lawsuit.

No definition available.

Name:	rdn_InsuranceCertificatesIssuedUnderMultipleInsurancePolicies
Namespace Prefix:	rdn_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Insurance Certificates Whose Scopes Were Narrowed as a Result of the Confidential Agreement

+ References

No definition available.

+ Details

Name:	rdn_InsuranceCertificatesWhoseScopesWereNarrowedasaResultoftheConfidentialAgreement
Namespace Prefix:	rdn_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Under Our Master Insurance Policy Any Suit Or Action Arising From Any Right Of The Insured Under The Policy Must Be Commenced Within This Number Of Years After Such Right First Arose

+ References

No definition available.

+ Details

Name:	rdn_LossContingencyLegalActionsCommencementPeriod
Namespace Prefix:	rdn_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

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

- Definition

Number of pending claims pertaining to a loss contingency.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14435-108349

+ Details

Name:	us-gaap_LossContingencyPendingClaimsNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=us-gaap_UnassertedClaimMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=rdn_TotalPrimaryInsuranceMortgageInsuranceProductsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=us-gaap_InsuranceClaimsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=rdn_PoolInsuranceMortgageInsuranceProductMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LitigationCaseAxis=rdn_InitialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LitigationCaseAxis=rdn_AmendedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Note 13 - Commitments and Contingencies Legal Proceedings (Details)	3 Months Ended
	Mar. 31, 2018 matter	Apr. 12, 2018 Certificates	Jun. 05, 2017 Certificates	Dec. 17, 2016 Certificates
Unasserted Claim [Member] \| Minimum [Member]
Loss Contingencies [Line Items]
Minimum Number of Pending or Threatened Matters That Could Affect Our Results \| matter	1
Total Primary Insurance Mortgage Insurance Products [Member] \| Insurance Claims [Member]
Loss Contingencies [Line Items]
Loss Contingency, Legal Actions Commencement, Period	2 years
Pool Insurance Mortgage Insurance Product [Member] \| Insurance Claims [Member]
Loss Contingencies [Line Items]
Loss Contingency, Legal Actions Commencement, Period	3 years
Initial [Member]
Loss Contingencies [Line Items]
Insurance Certificates Issued Under Multiple Insurance Policies				9,420
Ocwen Filings [Member]
Loss Contingencies [Line Items]
Insurance Certificates Issued Under Multiple Insurance Policies			8,870
Subsequent Event [Member] \| Ocwen Filings [Member]
Loss Contingencies [Line Items]
Insurance Certificates Whose Scopes Were Narrowed as a Result of the Confidential Agreement		2,500,000