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Long-Term Debt - Additional Information (Detail) (USD $) | 3 Months Ended | 12 Months Ended | 1 Months Ended | 12 Months Ended | 1 Months Ended | 12 Months Ended | 1 Months Ended
--- | --- | --- | --- | --- | --- | --- | ---
Mar. 31, 2013 | Dec. 31, 2014 | Dec. 31, 2010 | Dec. 31, 2013 | Dec. 31, 2006 | Jul. 31, 2009 | Dec. 31, 2007 | Nov. 30, 2014
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Federal home loan bank stock |  | $ 10,688,000 us-gaap_FederalHomeLoanBankStock |  |  |  |  |  |
Convertible notes | 288,000,000 us-gaap_ConvertibleNotesPayable |  |  |  |  |  |  |
Debt instrument interest rate | 4.625%us-gaap_DebtInstrumentInterestRateStatedPercentage |  |  |  |  |  |  |
Debt instrument maturity year | 2018 |  |  |  |  |  |  |
Debt instrument redemption date | Apr. 15, 2018 |  |  |  |  |  |  |
Net proceeds from issuance of convertible debt | 279,000,000 us-gaap_ProceedsFromDebtNetOfIssuanceCosts |  |  |  |  |  |  |
Interest expense yield |  | 5.45%us-gaap_DebtInstrumentInterestRateDuringPeriod |  |  |  |  |  |
Accrued interest payable |  | 1,900,000 us-gaap_InterestPayableCurrent |  |  |  |  |  |
Convertible senior notes conversion rate |  | 41.1320 us-gaap_DebtInstrumentConvertibleConversionRatio1 |  |  |  |  |  |
Debt instrument convertible base principal amount of conversion |  | 1,000 rwt_DebtInstrumentConvertibleBasePrincipalAmountOfConversion |  |  |  |  |  |
Convertible senior notes conversion per share |  | $ 24.31 us-gaap_DebtInstrumentConvertibleConversionPrice1 |  |  |  |  |  |
Accrued interest payable balance on long-term debt |  | 8,502,000 us-gaap_InterestPayableCurrentAndNoncurrent |  | 6,366,000 us-gaap_InterestPayableCurrentAndNoncurrent |  |  |  |
FHLB Chicago |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Federal home loan bank advances |  | 496,000,000 us-gaap_FederalHomeLoanBankAdvancesLongTerm / us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis = us-gaap_FederalHomeLoanBankOfChicagoMember |  |  |  |  |  |
Weighted average interest rate |  | 0.29%us-gaap_LongtermDebtWeightedAverageInterestRate / us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis = us-gaap_FederalHomeLoanBankOfChicagoMember |  |  |  |  |  |
Weighted average maturity |  | 9 years 4 months 24 days |  |  |  |  |  |
Federal home loan bank advances, Maturity period, Rate |  | 91 days |  |  |  |  |  |
Federal home loan bank stock |  | 11,000,000 us-gaap_FederalHomeLoanBankStock / us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis = us-gaap_FederalHomeLoanBankOfChicagoMember |  |  |  |  |  |
Residential Loans Held For Investment at Fair Value | FHLB Chicago |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Amount on advances secured by residential mortgage loans |  | 580,000,000 us-gaap_LoansReceivableFairValueDisclosure / us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis = us-gaap_FederalHomeLoanBankOfChicagoMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = rwt_ResidentialLoansHeldForInvestmentAtFairValueMember |  |  |  |  |  |
Maximum |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Accrued interest payable |  |  |  | 1,000,000 us-gaap_InterestPayableCurrent / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |  |
Commercial Secured Borrowings |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Commercial mortgage loans |  | 67,000,000 us-gaap_PledgedAssetsSeparatelyReportedMortgageRelatedSecuritiesAvailableForSaleOrHeldForInvestment / us-gaap_DebtInstrumentAxis = rwt_CommercialSecuredLoanMember |  |  |  |  |  |
Senior Notes due 2018 |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Accrued interest payable |  | 3,200,000 us-gaap_InterestPayableCurrent / us-gaap_DebtInstrumentAxis = us-gaap_SeniorNotesMember |  |  |  |  |  |
Unamortized deferred issuance costs |  | 5,800,000 us-gaap_UnamortizedDebtIssuanceExpense / us-gaap_DebtInstrumentAxis = us-gaap_SeniorNotesMember |  |  |  |  |  |
Trust Preferred Securities |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Interest expense yield |  | 2.58%us-gaap_DebtInstrumentInterestRateDuringPeriod / us-gaap_DebtInstrumentAxis = rwt_TrustPreferredSecuritiesMember |  | 2.64%us-gaap_DebtInstrumentInterestRateDuringPeriod / us-gaap_DebtInstrumentAxis = rwt_TrustPreferredSecuritiesMember |  |  |  |
Debt instrument face amount |  |  |  |  | 100,000,000 us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = rwt_TrustPreferredSecuritiesMember |  |  |
Debt instrument quarterly floating coupon rate basis |  |  |  |  | Three-month LIBOR plus 2.25% |  |  |
Debt instrument quarterly floating coupon rate |  |  |  |  | 2.25%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1 / us-gaap_DebtInstrumentAxis = rwt_TrustPreferredSecuritiesMember |  |  |
Debt instrument due date |  |  |  |  | Jan. 30, 2037 |  |  |
Percentage of yield of debt securities |  | 6.88%rwt_DebtInstrumentAverageInterestRate / us-gaap_DebtInstrumentAxis = rwt_TrustPreferredSecuritiesMember |  | 6.90%rwt_DebtInstrumentAverageInterestRate / us-gaap_DebtInstrumentAxis = rwt_TrustPreferredSecuritiesMember |  |  |  |
Earliest optional redemption date without penalty |  | Jan. 30, 2012 |  |  |  |  |  |
Principal amount of debt repurchased |  |  | 500,000 us-gaap_ExtinguishmentOfDebtAmount / us-gaap_DebtInstrumentAxis = rwt_TrustPreferredSecuritiesMember |  |  |  |  |
Subordinated Notes |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Interest expense yield |  | 2.58%us-gaap_DebtInstrumentInterestRateDuringPeriod / us-gaap_DebtInstrumentAxis = us-gaap_SeniorSubordinatedNotesMember |  | 2.64%us-gaap_DebtInstrumentInterestRateDuringPeriod / us-gaap_DebtInstrumentAxis = us-gaap_SeniorSubordinatedNotesMember |  |  |  |
Debt instrument face amount |  |  |  |  |  |  | 50,000,000 us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = us-gaap_SeniorSubordinatedNotesMember |
Debt instrument quarterly floating coupon rate basis |  |  |  |  |  |  | Three-month LIBOR plus 2.25% |
Debt instrument quarterly floating coupon rate |  |  |  |  |  |  | 2.25%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1 / us-gaap_DebtInstrumentAxis = us-gaap_SeniorSubordinatedNotesMember |
Debt instrument due date |  |  |  |  |  |  | Jul. 30, 2037 |
Percentage of yield of debt securities |  | 6.88%rwt_DebtInstrumentAverageInterestRate / us-gaap_DebtInstrumentAxis = us-gaap_SeniorSubordinatedNotesMember |  | 6.90%rwt_DebtInstrumentAverageInterestRate / us-gaap_DebtInstrumentAxis = us-gaap_SeniorSubordinatedNotesMember |  |  |  |
Earliest optional redemption date without penalty |  | Jul. 30, 2012 |  |  |  |  |  |
Principal amount of debt repurchased |  |  |  |  |  | 10,000,000 us-gaap_ExtinguishmentOfDebtAmount / us-gaap_DebtInstrumentAxis = us-gaap_SeniorSubordinatedNotesMember |  |
Long-term Debt | Maximum |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Accrued interest payable balance on long-term debt |  | 1,000,000 us-gaap_InterestPayableCurrentAndNoncurrent / us-gaap_DebtInstrumentAxis = us-gaap_LongTermDebtMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  | 1,000,000 us-gaap_InterestPayableCurrentAndNoncurrent / us-gaap_DebtInstrumentAxis = us-gaap_LongTermDebtMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |  |
Exchangeable Notes |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Convertible notes |  |  |  |  |  |  |  | 205,000,000 us-gaap_ConvertibleNotesPayable / us-gaap_DebtInstrumentAxis = rwt_ExchangeableSeniorNotesMember
Debt instrument interest rate |  |  |  |  |  |  |  | 5.625%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = rwt_ExchangeableSeniorNotesMember
Debt instrument maturity year |  |  |  |  |  |  |  | 2019
Debt instrument redemption date |  |  |  |  |  |  |  | Nov. 15, 2019
Net proceeds from issuance of convertible debt |  |  |  |  |  |  |  | 198,000,000 us-gaap_ProceedsFromDebtNetOfIssuanceCosts / us-gaap_DebtInstrumentAxis = rwt_ExchangeableSeniorNotesMember
Interest expense yield |  | 6.41%us-gaap_DebtInstrumentInterestRateDuringPeriod / us-gaap_DebtInstrumentAxis = rwt_ExchangeableSeniorNotesMember |  |  |  |  |  |
Accrued interest payable |  | 1,200,000 us-gaap_InterestPayableCurrent / us-gaap_DebtInstrumentAxis = rwt_ExchangeableSeniorNotesMember |  |  |  |  |  |
Unamortized deferred issuance costs |  | 6,800,000 us-gaap_UnamortizedDebtIssuanceExpense / us-gaap_DebtInstrumentAxis = rwt_ExchangeableSeniorNotesMember |  |  |  |  |  |
Convertible senior notes conversion rate |  | 46.1798 us-gaap_DebtInstrumentConvertibleConversionRatio1 / us-gaap_DebtInstrumentAxis = rwt_ExchangeableSeniorNotesMember |  |  |  |  |  |
Debt instrument convertible base principal amount of conversion |  | $ 1,000 rwt_DebtInstrumentConvertibleBasePrincipalAmountOfConversion / us-gaap_DebtInstrumentAxis = rwt_ExchangeableSeniorNotesMember |  |  |  |  |  |
Convertible senior notes conversion per share |  | $ 21.65 us-gaap_DebtInstrumentConvertibleConversionPrice1 / us-gaap_DebtInstrumentAxis = rwt_ExchangeableSeniorNotesMember |  |  |  |  |  |

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- Definition Including the current and noncurrent portions, carrying value as of the balance sheet date of a written promise to pay a note, initially due after one year or beyond the operating cycle if longer, which can be exchanged for a specified amount of one or more securities (typically common stock), at the option of the issuer or the holder. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16(a)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 9 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20, 22 -Article 5 + Details
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- Definition Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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- Definition Including both current and noncurrent portions, Federal Home Loan Bank borrowings initially due beyond one year or beyond the normal operating cycle if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 9 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64702-112823 + Details
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- Definition Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Glossary Loan -URI http://asc.fasb.org/extlink&oid=6517073 + Details
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