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Geographic Concentrate of Commercial Loans Recorded on Consolidated Balance Sheet (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Commercial Loans Held For Sale
Concentration Risk [Line Items]
Concentration risk percentage	100.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_CommercialLoansHeldForSaleMember	100.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_CommercialLoansHeldForSaleMember
Commercial Loans Held For Investment
Concentration Risk [Line Items]
Concentration risk percentage	100.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_CommercialLoansHeldForInvestmentMember	100.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_CommercialLoansHeldForInvestmentMember
Other states | Commercial Loans Held For Sale
Concentration Risk [Line Items]
Concentration risk percentage	8.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_CommercialLoansHeldForSaleMember / us-gaap_StatementGeographicalAxis = rwt_OtherStateMember
Other states | Commercial Loans Held For Investment
Concentration Risk [Line Items]
Concentration risk percentage	32.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_CommercialLoansHeldForInvestmentMember / us-gaap_StatementGeographicalAxis = rwt_OtherStateMember	29.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_CommercialLoansHeldForInvestmentMember / us-gaap_StatementGeographicalAxis = rwt_OtherStateMember
Maximum | Other states | Commercial Loans Held For Sale
Concentration Risk [Line Items]
Concentration risk percentage	5.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_CommercialLoansHeldForSaleMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_StatementGeographicalAxis = rwt_OtherStateMember	5.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_CommercialLoansHeldForSaleMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_StatementGeographicalAxis = rwt_OtherStateMember
Maximum | Other states | Commercial Loans Held For Investment
Concentration Risk [Line Items]
Concentration risk percentage	5.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_CommercialLoansHeldForInvestmentMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_StatementGeographicalAxis = rwt_OtherStateMember	5.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_CommercialLoansHeldForInvestmentMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_StatementGeographicalAxis = rwt_OtherStateMember

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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 21

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13537-108611



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13531-108611



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 18

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592

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