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Residential Loans - Additional Information (Detail) (USD $) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2015 Contract | Mar. 31, 2014 | Dec. 31, 2014 Contract
Mortgage Loans on Real Estate [Line Items] |  |  |
Principal balance of loans sold during period | $ 2,200,000,000 rwt_PrincipalBalanceofLoansSoldDuringPeriod | $ 707,000,000 rwt_PrincipalBalanceofLoansSoldDuringPeriod |
Carrying value | 3,399,755,000 us-gaap_LoansAndLeasesReceivableNetReportedAmountConsumer |  | 3,398,573,000 us-gaap_LoansAndLeasesReceivableNetReportedAmountConsumer
Sequoia |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Carrying value | 1,304,426,000 us-gaap_LoansAndLeasesReceivableNetReportedAmountConsumer / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = rwt_SequoiaSecuritizationEntitiesMember |  | 1,474,386,000 us-gaap_LoansAndLeasesReceivableNetReportedAmountConsumer / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = rwt_SequoiaSecuritizationEntitiesMember
Fixed-rate loans |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Weighted average coupon rate | 3.92%rwt_FinancingReceivablesWeightedAverageInterestRate / us-gaap_FinancialInstrumentAxis = us-gaap_FixedRateResidentialMortgageMember |  |
Hybrid loans |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Weighted average coupon rate | 3.06%rwt_FinancingReceivablesWeightedAverageInterestRate / us-gaap_FinancialInstrumentAxis = rwt_HybridResidentialMortgagesMember |  |
Residential Loans at Fair Value |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Number of loans | 1,903 us-gaap_MortgageLoansOnRealEstateNumberOfLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansAtFairValueMember |  | 2,273 us-gaap_MortgageLoansOnRealEstateNumberOfLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansAtFairValueMember
Loan Principal | 1,070,000,000 us-gaap_PrincipalAmountOutstandingOnLoansManagedAndSecuritized / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansAtFairValueMember |  | 1,300,000,000 us-gaap_PrincipalAmountOutstandingOnLoansManagedAndSecuritized / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansAtFairValueMember
Principal value of loans purchased | 2,400,000,000 rwt_PrincipalBalanceOfLoansAcquiredDuringPeriod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansAtFairValueMember | 1,070,000,000 rwt_PrincipalBalanceOfLoansAcquiredDuringPeriod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansAtFairValueMember |
Valuation adjustments | 2,056,000 us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansAtFairValueMember | 7,128,000 us-gaap_FairValueOptionChangesInFairValueGainLoss1 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansAtFairValueMember |
Residential Loans at Lower of Cost or Fair Value |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Number of loans | 9 us-gaap_MortgageLoansOnRealEstateNumberOfLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansAtLowerOfCostOrFairValueMember |  | 9,000 us-gaap_MortgageLoansOnRealEstateNumberOfLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansAtLowerOfCostOrFairValueMember
Loan Principal | 2,000,000 us-gaap_PrincipalAmountOutstandingOnLoansManagedAndSecuritized / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansAtLowerOfCostOrFairValueMember |  | 0 us-gaap_PrincipalAmountOutstandingOnLoansManagedAndSecuritized / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansAtLowerOfCostOrFairValueMember
Carrying value | 1,472,000 us-gaap_LoansAndLeasesReceivableNetReportedAmountConsumer / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansAtLowerOfCostOrFairValueMember |  | 1,488,000 us-gaap_LoansAndLeasesReceivableNetReportedAmountConsumer / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansAtLowerOfCostOrFairValueMember
Residential Loans at Lower of Cost or Fair Value | Sequoia |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Carrying value | 0 us-gaap_LoansAndLeasesReceivableNetReportedAmountConsumer / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansAtLowerOfCostOrFairValueMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = rwt_SequoiaSecuritizationEntitiesMember |  | 0 us-gaap_LoansAndLeasesReceivableNetReportedAmountConsumer / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansAtLowerOfCostOrFairValueMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = rwt_SequoiaSecuritizationEntitiesMember
Residential Loans Held For Investment at Fair Value |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Number of loans | 1,314 us-gaap_MortgageLoansOnRealEstateNumberOfLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentAtFairValueMember |  | 803 us-gaap_MortgageLoansOnRealEstateNumberOfLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentAtFairValueMember
Loan Principal | 972,000,000 us-gaap_PrincipalAmountOutstandingOnLoansManagedAndSecuritized / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentAtFairValueMember |  | 566,000,000 us-gaap_PrincipalAmountOutstandingOnLoansManagedAndSecuritized / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentAtFairValueMember
Carrying value | 1,000,000,000 us-gaap_LoansAndLeasesReceivableNetReportedAmountConsumer / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentAtFairValueMember |  |
Principal balance of loans transferred | 436,000,000 rwt_PrincipalAmountOfLoansSecuritizedDuringPeriod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentAtFairValueMember |  |
Fair value of loans transferred | 448,000,000 rwt_FairValueOfLoansSecuritizedDuringPeriod / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentAtFairValueMember |  |
Loan pledged as collateral | 994,000,000 us-gaap_LoansPledgedAsCollateral / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentAtFairValueMember |  |
Weighted average original Fair Isaac Corporation (FICO) score | 773 rwt_FinancingReceivableCreditScoreFICOWeightedAverage / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentAtFairValueMember |  |
Weighted average original loan-to-value (LTV) | 68.00%rwt_FinancingReceivableLoanToValueRatio / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentAtFairValueMember |  |
Residential Loans Held For Investment at Fair Value | Sequoia |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Number of loans | 5,177 us-gaap_MortgageLoansOnRealEstateNumberOfLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentAtFairValueMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = rwt_SequoiaSecuritizationEntitiesMember |  | 5,315 us-gaap_MortgageLoansOnRealEstateNumberOfLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentAtFairValueMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = rwt_SequoiaSecuritizationEntitiesMember
Weighted average original Fair Isaac Corporation (FICO) score | 733 rwt_FinancingReceivableCreditScoreFICOWeightedAverage / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentAtFairValueMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = rwt_SequoiaSecuritizationEntitiesMember |  |
Weighted average original loan-to-value (LTV) | 66.00%rwt_FinancingReceivableLoanToValueRatio / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentAtFairValueMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = rwt_SequoiaSecuritizationEntitiesMember |  |
Loans held-for-investment, delinquent greater than 90 days | 68,000,000 us-gaap_FairValueOptionLoansHeldAsAssets90DaysOrMorePastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentAtFairValueMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = rwt_SequoiaSecuritizationEntitiesMember |  | 73,000,000 us-gaap_FairValueOptionLoansHeldAsAssets90DaysOrMorePastDue / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentAtFairValueMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = rwt_SequoiaSecuritizationEntitiesMember
Loans held-for-investment, in foreclosure | 34,000,000 rwt_FairValueOptionLoansHeldAsAssetsAggregateAmountInForeclosure / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentAtFairValueMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = rwt_SequoiaSecuritizationEntitiesMember |  | 39,000,000 rwt_FairValueOptionLoansHeldAsAssetsAggregateAmountInForeclosure / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentAtFairValueMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = rwt_SequoiaSecuritizationEntitiesMember
Valuation adjustments | 3,000,000 us-gaap_MortgageLoansOnRealEstatePeriodIncreaseDecrease / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentAtFairValueMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = rwt_SequoiaSecuritizationEntitiesMember |  |
Residential Loans Held for Investment |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Loan Principal | 1,415,017,000 us-gaap_PrincipalAmountOutstandingOnLoansManagedAndSecuritized / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentMember |  | 1,483,213,000 us-gaap_PrincipalAmountOutstandingOnLoansManagedAndSecuritized / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentMember
Carrying value | 1,304,426,000 us-gaap_LoansAndLeasesReceivableNetReportedAmountConsumer / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentMember |  | 1,474,386,000 us-gaap_LoansAndLeasesReceivableNetReportedAmountConsumer / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentMember
Unamortized premium, net | 0 us-gaap_UnamortizedLoanCommitmentAndOriginationFeesAndUnamortizedDiscountsOrPremiums / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentMember |  | 12,511,000 us-gaap_UnamortizedLoanCommitmentAndOriginationFeesAndUnamortizedDiscountsOrPremiums / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentMember
Allowance for loan losses | 0 us-gaap_AllowanceForLoanAndLeaseLossesRealEstate / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentMember |  | 21,338,000 us-gaap_AllowanceForLoanAndLeaseLossesRealEstate / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentMember
Mortgage Servicing Rights |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Purchases of mortgage servicing assets | $ 1,908,993,000 us-gaap_ServicingAssetAtAmortizedValueAdditions / us-gaap_InvestmentTypeAxis = rwt_MortgageServicingRightsMember |  |

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- Definition The weighted average FICO score for borrowers at the time loans were originated. + References No definition available. + Details
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- Definition Principal Balance of Loans Sold During Period + References No definition available. + Details
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- Definition The reserve to cover probable credit losses related to specifically identified fixed maturity real estate loans as well as probable credit losses inherent in the remainder of that loan portfolio. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 310 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6873192&loc=d3e21338-158488 + Details
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- Definition This item represents the aggregate fair value of loans held as assets that are 90 days or more past due for which the fair value option has been elected. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 28 -Subparagraph (e)(1) -URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14064-108612 + Details
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- Definition Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of consumer loans, including, but not limited to, mortgage, home equity, vehicles, credit card, installment, and lease financing. Excludes loans and leases covered under loss sharing agreements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5074-111524 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5066-111524 + Details
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- Definition Carrying amount as of the balance sheet date of loans that have been pledged as collateral for borrowings. If the secured party has the right by contract or custom to sell or re-pledge the collateral, then the debtor reclassifies that asset and report that asset in its statement of financial position separately from other assets not so encumbered. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5086-111524 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6467456&loc=d3e113888-111728 + Details
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- Definition Amount of deferred fees paid by borrowers and unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of loans that are being amortized into income as an adjustment to yield. Excludes amounts for loans and leases covered under loss sharing agreements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6378536&loc=d3e10092-111533 + Details
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