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Fair Value of Financial Instruments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Residential Subordinate Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	$ 9rwt_FairValueOptionAssetsAggregateCarryingAmountDuringPeriod / invest_InvestmentSecuritiesClassAxis = rwt_ResidentialSubordinateSecuritiesMember	$ 4rwt_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	8,810rwt_FairValueOptionAssetsAggregateCarryingAmountDuringPeriod / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialMortgageMember	7,090rwt_FairValueOptionAssetsAggregateCarryingAmountDuringPeriod / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialMortgageMember
Mortgage Servicing Rights
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	96rwt_FairValueOptionAssetsAggregateCarryingAmountDuringPeriod / invest_InvestmentSecuritiesClassAxis = rwt_MortgageServicingRightsMember	48rwt_FairValueOptionAssetsAggregateCarryingAmountDuringPeriod / invest_InvestmentSecuritiesClassAxis = rwt_MortgageServicingRightsMember
Guarantee Asset
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	7rwt_FairValueOptionAssetsAggregateCarryingAmountDuringPeriod / invest_InvestmentSecuritiesClassAxis = rwt_AssetValueGuaranteesMember
Senior Securities | Residential
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	77rwt_FairValueOptionAssetsAggregateCarryingAmountDuringPeriod / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_InvestmentTypeAxis = rwt_SeniorSecuritiesMember	105rwt_FairValueOptionAssetsAggregateCarryingAmountDuringPeriod / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember / us-gaap_InvestmentTypeAxis = rwt_SeniorSecuritiesMember
Senior Loans | Commercial Loans
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	$ 935rwt_FairValueOptionAssetsAggregateCarryingAmountDuringPeriod / invest_InvestmentSecuritiesClassAxis = us-gaap_CommercialLoanMember / us-gaap_InvestmentTypeAxis = us-gaap_SeniorLoansMember	$ 505rwt_FairValueOptionAssetsAggregateCarryingAmountDuringPeriod / invest_InvestmentSecuritiesClassAxis = us-gaap_CommercialLoanMember / us-gaap_InvestmentTypeAxis = us-gaap_SeniorLoansMember
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]
Percentage difference of internal valuation than dealer marks	1.00%rwt_PercentageDifferenceOfInternalValuationThanDealerMarks / us-gaap_InvestmentTypeAxis = us-gaap_AssetBackedSecuritiesMember
Dealer marks of securities	44.00%rwt_PercentageOfDealerQuotesReceivedOnSecurities / us-gaap_InvestmentTypeAxis = us-gaap_AssetBackedSecuritiesMember

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