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Geographic Concentration of Residential Loans Recorded on Consolidated Balance Sheet (Parenthetical) (Detail) (Maximum, Other states)
Dec. 31, 2014
Dec. 31, 2013
Residential Loans Held For Sale
    
Concentration Risk [Line Items]    
Concentration risk percentage per other state 5.00%rwt_ConcentrationRiskPercentagePerOtherState
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= rwt_ResidentialLoansHeldForSaleMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_StatementGeographicalAxis
= rwt_OtherStateMember		 5.00%rwt_ConcentrationRiskPercentagePerOtherState
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= rwt_ResidentialLoansHeldForSaleMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_StatementGeographicalAxis
= rwt_OtherStateMember
Residential Loans Held for Investment
    
Concentration Risk [Line Items]    
Concentration risk percentage per other state 5.00%rwt_ConcentrationRiskPercentagePerOtherState
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= rwt_ResidentialLoansHeldForInvestmentMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_StatementGeographicalAxis
= rwt_OtherStateMember		 5.00%rwt_ConcentrationRiskPercentagePerOtherState
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= rwt_ResidentialLoansHeldForInvestmentMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_StatementGeographicalAxis
= rwt_OtherStateMember
Residential Loans Held For Investment at Fair Value
    
Concentration Risk [Line Items]    
Concentration risk percentage per other state 5.00%rwt_ConcentrationRiskPercentagePerOtherState
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= rwt_ResidentialLoansHeldForInvestmentAtFairValueMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_StatementGeographicalAxis
= rwt_OtherStateMember