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Summary of Significant Valuation Assumptions for Available for Sale Securities (Detail)	12 Months Ended
	Dec. 31, 2014
Prime | Minimum
Schedule of Available-for-sale Securities [Line Items]
Prepayment rates	8.00%rwt_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosurePrepaymentRates / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialPrimeFinancingReceivableMember / us-gaap_RangeAxis = us-gaap_MinimumMember
Loss severity	20.00%rwt_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureLossSeverity / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialPrimeFinancingReceivableMember / us-gaap_RangeAxis = us-gaap_MinimumMember
Projected default rate	1.00%us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureOtherDefaultRate / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialPrimeFinancingReceivableMember / us-gaap_RangeAxis = us-gaap_MinimumMember
Prime | Maximum
Schedule of Available-for-sale Securities [Line Items]
Prepayment rates	15.00%rwt_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosurePrepaymentRates / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialPrimeFinancingReceivableMember / us-gaap_RangeAxis = us-gaap_MaximumMember
Loss severity	52.00%rwt_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureLossSeverity / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialPrimeFinancingReceivableMember / us-gaap_RangeAxis = us-gaap_MaximumMember
Projected default rate	22.00%us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureOtherDefaultRate / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialPrimeFinancingReceivableMember / us-gaap_RangeAxis = us-gaap_MaximumMember
Non-prime | Minimum
Schedule of Available-for-sale Securities [Line Items]
Prepayment rates	10.00%rwt_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosurePrepaymentRates / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialSubprimeFinancingReceivableMember / us-gaap_RangeAxis = us-gaap_MinimumMember
Loss severity	35.00%rwt_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureLossSeverity / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialSubprimeFinancingReceivableMember / us-gaap_RangeAxis = us-gaap_MinimumMember
Projected default rate	15.00%us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureOtherDefaultRate / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialSubprimeFinancingReceivableMember / us-gaap_RangeAxis = us-gaap_MinimumMember
Non-prime | Maximum
Schedule of Available-for-sale Securities [Line Items]
Prepayment rates	10.00%rwt_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosurePrepaymentRates / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialSubprimeFinancingReceivableMember / us-gaap_RangeAxis = us-gaap_MaximumMember
Loss severity	35.00%rwt_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureLossSeverity / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialSubprimeFinancingReceivableMember / us-gaap_RangeAxis = us-gaap_MaximumMember
Projected default rate	15.00%us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureOtherDefaultRate / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialSubprimeFinancingReceivableMember / us-gaap_RangeAxis = us-gaap_MaximumMember

X

- Definition

This item represents a significant valuation assumption on loss severity, represented as a percentage, which was considered as one of the potential factors in reaching a conclusion that the available-for-sale investments are not other-than-temporarily impaired.

+ References

No definition available.

+ Details

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X

- Definition

This item represents a significant valuation assumption on prepayment rates, represented as a percentage, which was considered as one of the potential factors in reaching a conclusion that the available-for-sale investments are not other-than-temporarily impaired.

+ References

No definition available.

+ Details

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Namespace Prefix:	rwt_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

This item represents the default rate of the underlying assets in the security that were considered as one of the potential factors in reaching a conclusion that the available-for-sale investments are not other-than-temporarily impaired.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563

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X

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