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Fair Value of Financial Instruments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Dealer marks of securities	81.00%rwt_PercentageOfDealerQuotesReceivedOnSecurities
Percentage of carrying value for which dealer quotes have been received	93.00%rwt_PercentageOfCarryingValueForWhichDealerQuotesWereReceivedOnSecurities
Percentage difference of internal valuation than dealer marks	2.00%rwt_PercentageDifferenceOfInternalValuationThanDealerMarks
Residential Subordinate Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	$ 23rwt_FairValueOptionAssetsAggregateCarryingAmountDuringPeriod / invest_InvestmentSecuritiesClassAxis = rwt_ResidentialSubordinateSecuritiesMember
Residential Loans
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	2,400rwt_FairValueOptionAssetsAggregateCarryingAmountDuringPeriod / invest_InvestmentSecuritiesClassAxis = rwt_ResidentialLoansMember
Commercial Loans
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	93rwt_FairValueOptionAssetsAggregateCarryingAmountDuringPeriod / invest_InvestmentSecuritiesClassAxis = us-gaap_CommercialLoanMember
Mortgage Servicing Rights
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	$ 19rwt_FairValueOptionAssetsAggregateCarryingAmountDuringPeriod / invest_InvestmentSecuritiesClassAxis = rwt_MortgageServicingRightsMember
Mortgage Servicing Rights | Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Percentage difference of internal valuation than dealer marks	2.00%rwt_PercentageDifferenceOfInternalValuationThanDealerMarks / us-gaap_InvestmentTypeAxis = rwt_MortgageServicingRightsMember / us-gaap_RangeAxis = us-gaap_MaximumMember
Asset-backed Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Dealer marks of securities	36.00%rwt_PercentageOfDealerQuotesReceivedOnSecurities / us-gaap_InvestmentTypeAxis = us-gaap_AssetBackedSecuritiesMember
Percentage difference of internal valuation than dealer marks	1.00%rwt_PercentageDifferenceOfInternalValuationThanDealerMarks / us-gaap_InvestmentTypeAxis = us-gaap_AssetBackedSecuritiesMember

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