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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
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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 |

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- Definition Concentration Risk, Percentage, Per Other State + References No definition available. + Details
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Namespace Prefix: | rwt_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration