Business Purpose Loans - Activity and Characteristics of Business Purpose Loans (Details) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2021 USD ($) loan	Mar. 31, 2020 USD ($) loan	Dec. 31, 2020 USD ($) loan
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Purchases of held-for-sale loans	$ 3,150,432	$ 2,665,447
Principal balance of loans sold to third parties	11,746	11,952
Transfers from loans held-for-sale to loans held-for-investment	$ 301,298	382,635
Number of loans transferred \| loan	2
Transfers from residential loans to real estate owned	$ 14,684	6,363
Commitment To Fund Residential Bridge Loan
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Commitment to fund loan	283,000
Single-family rental loans, held-for-sale \| Redwood
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Purchases of held-for-sale loans	253,098	260,129
Principal balance of loans sold to third parties	0	26,148
Transfers from loans held-for-sale to loans held-for-investment	169,404	378,109
Gain (loss) on investments	0	(23,028)
Fair value of loans	333,110		$ 245,394
Single-family rental loans, held-for-sale \| Redwood \| Business Purpose Mortgage Banking Activities, Net:
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Gain (loss) on investments	10,248	10,330
Single-family rental loans, held-for-sale \| CAFL
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Purchases of held-for-sale loans	$ 169,000	$ 378,000
Number of securitization entities to which asset transferred (in entities) \| loan	1	1
Single-family rental loans held-for-investment \| Redwood
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Fair value of loans	$ 0		$ 0
Single-family rental loans held-for-investment \| CAFL
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Gain (loss) on investments	$ (60,901)	$ (271,917)
Number of loans \| loan	1,120		1,094
Unpaid principal balance	$ 3,029,498		$ 3,017,137
Fair value of loans	$ 3,212,526		$ 3,249,194
Weighted average coupon rate	5.41%		5.44%
Contract maturities	5 years		5 years
Fair value of loans with 90+ day delinquencies	$ 21,234		$ 24,745
Number of loans in foreclosure \| loan	11		10
Single-family rental loans held-for-investment \| CAFL \| Financing Receivables, Equal to Greater than 90 Days Past Due
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of loans with 90+ day delinquencies \| loan	21		22
Fair value of loans with 90+ day delinquencies	$ 57,985		$ 61,440
Bridge loans held-for-investment
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Purchases of held-for-sale loans	133,229	227,368
Principal balance of loans sold to third parties	8,877	20,735
Gain (loss) on investments	$ 3,304	(38,602)
Adjustable rate (as a percent)	58.00%
Fixed rate (as a percent)	42.00%
Transfers from residential loans to real estate owned	$ 1,000
Fair value of loans	$ 626,484		641,765
Bridge loans held-for-investment \| Minimum
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Residential bridge loans held-for-investment, original maturities (in months)	6 months
Bridge loans held-for-investment \| Maximum
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Residential bridge loans held-for-investment, original maturities (in months)	24 months
Bridge loans held-for-investment \| Business Purpose Mortgage Banking Activities, Net:
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Gain (loss) on investments	$ 542	(164)
Business Purpose Loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Fee income	6,000	$ 8,000
Fair value of loans	$ 4,172,120		$ 4,136,353
Single-Family Rental Loans, Held-For-Sale \| Redwood
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of loans \| loan	77		65
Unpaid principal balance	$ 322,181		$ 234,475
Fair value of loans	$ 333,110		$ 245,394
Weighted average coupon rate	4.84%		4.84%
Contract maturities	7 years		8 years
Fair value of loans with 90+ day delinquencies	$ 5,976		$ 0
Number of loans in foreclosure \| loan	7		0
Unpaid principal balance of loans in foreclosure	$ 4,808		$ 0
Single-Family Rental Loans, Held-For-Sale \| Redwood \| Loans Pledged As Collateral, Short Term Debt
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Gain (loss) on investments	74,733		34,098
Single-Family Rental Loans, Held-For-Sale \| Redwood \| Loans Pledged As Collateral, Long Term debt
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Gain (loss) on investments	$ 228,125		$ 154,774
Single-Family Rental Loans, Held-For-Sale \| Redwood \| Financing Receivables, Equal to Greater than 90 Days Past Due
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of loans with 90+ day delinquencies \| loan	9		10
Fair value of loans with 90+ day delinquencies	$ 6,883		$ 7,127
Unpaid principal balance of loans with 90+ day delinquencies	$ 5,676		$ 6,143
Business Purpose Bridge Loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of loans \| loan	2,097		1,725
Unpaid principal balance	$ 629,934		$ 649,532
Fair value of loans	$ 626,484		$ 641,765
Weighted average coupon rate	7.93%		8.09%
Contract maturities	1 year		1 year
Fair value of loans with 90+ day delinquencies	$ 20,424		$ 38,552
Number of loans in foreclosure \| loan	57		25
Unpaid principal balance of loans in foreclosure	$ 17,183		$ 33,066
Business Purpose Bridge Loans \| Loans Pledged As Collateral, Short Term Debt
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Gain (loss) on investments	90,096		92,931
Business Purpose Bridge Loans \| Loans Pledged As Collateral, Long Term debt
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Gain (loss) on investments	$ 522,050		$ 544,151
Business Purpose Bridge Loans \| Financing Receivables, Equal to Greater than 90 Days Past Due
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of loans with 90+ day delinquencies \| loan	31		31
Fair value of loans with 90+ day delinquencies	$ 17,850		$ 39,415
Unpaid principal balance of loans with 90+ day delinquencies	$ 14,556		$ 33,605

Fair Value, Option, Loans Held As Assets, Aggregate Amount In Foreclosure

No definition available.

Name:	rwt_FairValueOptionLoansHeldAsAssetsAggregateAmountInForeclosure
Namespace Prefix:	rwt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financing Receivable, Contract Maturities

+ References

No definition available.

+ Details

Name:	rwt_FinancingReceivableContractMaturities
Namespace Prefix:	rwt_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Financing Receivable, Number Of Loans In Foreclosure

+ References

No definition available.

+ Details

Name:	rwt_FinancingReceivableNumberOfLoansInForeclosure
Namespace Prefix:	rwt_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Financing Receivable, Number Of Loans Past Due

+ References

No definition available.

+ Details

Name:	rwt_FinancingReceivableNumberOfLoansPastDue
Namespace Prefix:	rwt_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Financing Receivables, Weighted Average Interest Rate

+ References

No definition available.

+ Details

Name:	rwt_FinancingReceivablesWeightedAverageInterestRate
Namespace Prefix:	rwt_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of Securitization Entities to which Asset Transferred

+ References

No definition available.

+ Details

Name:	rwt_NumberOfSecuritizationEntitiesToWhichAssetTransferred
Namespace Prefix:	rwt_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The cash inflow from repayments of the balance excluding interest (principal) on real estate securities.

+ References

No definition available.

+ Details

Name:	rwt_ProceedsFromPrincipalRepaymentsOnSecurities
Namespace Prefix:	rwt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Real Estate Owned, Held-for-Investment, Adjustable Rate, Percent

+ References

No definition available.

+ Details

Name:	rwt_RealEstateOwnedHeldForInvestmentAdjustableRatePercent
Namespace Prefix:	rwt_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Real Estate Owned, Held-for-Investment, Fixed Rate, Percentage

+ References

No definition available.

+ Details

Name:	rwt_RealEstateOwnedHeldForInvestmentFixedRatePercentage
Namespace Prefix:	rwt_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Real Estate Owned, Held-for-Investment, Original Maturity, Term

+ References

No definition available.

+ Details

Name:	rwt_RealEstateOwnedHeldForInvestmentOriginalMaturityTerm
Namespace Prefix:	rwt_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Real Estate Owned, Transfer to Real Estate Owned, Number Of Loans

+ References

No definition available.

+ Details

Name:	rwt_RealEstateOwnedTransfertoRealEstateOwnedNumberOfLoans
Namespace Prefix:	rwt_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Servicing Fees 1

+ References

No definition available.

+ Details

Name:	rwt_ServicingFees1
Namespace Prefix:	rwt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	srt_MortgageLoansOnRealEstateLineItems
Namespace Prefix:	srt_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of mortgage loans within investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 12
-Footnote 3
-Subsection 29

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29(Footnote 3))
-URI http://asc.fasb.org/extlink&oid=120402547&loc=d3e617274-123014

+ Details

Name:	srt_MortgageLoansOnRealEstateNumberOfLoans
Namespace Prefix:	srt_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- 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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (e)(1)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

+ Details

Name:	us-gaap_FairValueOptionLoansHeldAsAssets90DaysOrMorePastDue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of financing receivable past due.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 80
-URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922355-210448

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919253-210447

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953401-111524

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentPastDue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of realized and unrealized gain (loss) on investment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27405-111563

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.7(c),9(a))
-URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227

Reference 3: http://www.xbrl.org/2003/role/recommendedDisclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

+ Details

Name:	us-gaap_GainLossOnInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount, after allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919230-210447

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=121593590&loc=d3e4428-111522

+ Details

Name:	us-gaap_NotesReceivableNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

+ References

No definition available.

+ Details

Name:	us-gaap_OtherCommitment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The aggregate cash outflow used to purchase all loans that are held with the intention to resell in the near future.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 21
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3461-108585

+ Details

Name:	us-gaap_PaymentsToPurchaseLoansHeldForSale
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This is the sum of principal amount outstanding for both securitized and unsecuritized loans of all types.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121570589&loc=d3e107314-111719

+ Details

Name:	us-gaap_PrincipalAmountOutstandingOnLoansManagedAndSecuritized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Value of loans held-for-sale transferred to loans held in the entity's portfolio in noncash transactions.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=121583591&loc=d3e4304-108586

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=121583591&loc=d3e4332-108586

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=121583591&loc=d3e4313-108586

+ Details

Name:	us-gaap_TransferOfLoansHeldForSaleToPortfolioLoans1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Value transferred from mortgage loans to real estate owned (REO) in noncash transactions.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=121583591&loc=d3e4313-108586

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=121583591&loc=d3e4304-108586

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=121583591&loc=d3e4332-108586

+ Details

Name:	us-gaap_TransferToOtherRealEstate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_OtherCommitmentsAxis=rwt_CommitmentToFundResidentialBridgeLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=rwt_SingleFamilyRentalLoansHeldForSaleAtFairValueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=rwt_RedwoodTrustInc.Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=rwt_BusinessPurposeMortgageBankingActivitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=rwt_CAFLSecuritizationEntitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=rwt_SingleFamilyRentalLoansHeldForInvestmentAtFairValueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablesPeriodPastDueAxis=us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=rwt_ResidentialBridgeLoansHeldForInvestmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=rwt_BusinessPurposeResidentialLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=rwt_SingleFamilyRentalLoansHeldForSaleMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=rwt_LoansPledgedAsCollateralShortTermDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=rwt_LoansPledgedAsCollateralLongTermDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=rwt_BusinessPurposeBridgeLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: