Balance Sheet Parenthetical (Parentheticals) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fixed-maturities, Available-for-sale, Amortized Cost	$ 5,393,623	$ 4,549,534
Trading Securities, Amortized Cost	260,773	297,505
Equity Securities, Amortized Cost	145,501	125,311
Reinvested Cash Collateral Held Under Securities Lending Agreements	$ 15,587	$ 25,561

The value of the cash collateral that an entity received in a financing transaction in exchange for securities lent that has been reinvested. This amount is included in investments on the balance sheet.

No definition available.

+ Details

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Namespace Prefix:	rdn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121558606&loc=SL82898722-210454

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- Definition

Cost of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). Excludes equity method investment and investment in equity security without readily determinable fair value.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amortized cost of investments in debt securities classified as trading.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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