Principles of Consolidation - Assets and Liabilities of Consolidated Variable Interest Entity's (Details) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018 USD ($) Investment	Dec. 31, 2017 USD ($) Investment
Variable Interest Entity [Line Items]
Assets	$ 1,647,850	$ 1,259,774
Liabilities	1,546,066	1,167,157
Sequoia
Variable Interest Entity [Line Items]
Assets	1,647,850	1,259,774
Liabilities	$ 1,546,066	$ 1,167,157
Number of VIEs (in investments) \| Investment	23	22
Sequoia \| Residential loans held-for-investment, at Redwood
Variable Interest Entity [Line Items]
Assets	$ 1,639,770	$ 1,252,879
Sequoia \| Restricted cash
Variable Interest Entity [Line Items]
Assets	155	151
Sequoia \| Accrued interest receivable
Variable Interest Entity [Line Items]
Assets	4,810	3,391
Sequoia \| REO
Variable Interest Entity [Line Items]
Assets	3,115	3,353
Sequoia \| Accrued interest payable
Variable Interest Entity [Line Items]
Liabilities	3,972	2,568
Sequoia \| Accrued expenses and other liabilities
Variable Interest Entity [Line Items]
Liabilities	7	4
Sequoia \| Asset-backed securities issued
Variable Interest Entity [Line Items]
Liabilities	1,542,087	1,164,585
Legacy Sequoia
Variable Interest Entity [Line Items]
Assets	630,167	637,184
Liabilities	$ 616,383	$ 622,982
Number of VIEs (in investments) \| Investment	20	20
Legacy Sequoia \| Residential loans held-for-investment, at Redwood
Variable Interest Entity [Line Items]
Assets	$ 626,151	$ 632,817
Legacy Sequoia \| Restricted cash
Variable Interest Entity [Line Items]
Assets	148	147
Legacy Sequoia \| Accrued interest receivable
Variable Interest Entity [Line Items]
Assets	753	867
Legacy Sequoia \| REO
Variable Interest Entity [Line Items]
Assets	3,115	3,353
Legacy Sequoia \| Accrued interest payable
Variable Interest Entity [Line Items]
Liabilities	534	537
Legacy Sequoia \| Accrued expenses and other liabilities
Variable Interest Entity [Line Items]
Liabilities	0	0
Legacy Sequoia \| Asset-backed securities issued
Variable Interest Entity [Line Items]
Liabilities	615,849	622,445
Sequoia Choice
Variable Interest Entity [Line Items]
Assets	1,017,683	622,590
Liabilities	$ 929,683	$ 544,175
Number of VIEs (in investments) \| Investment	3	2
Sequoia Choice \| Residential loans held-for-investment, at Redwood
Variable Interest Entity [Line Items]
Assets	$ 1,013,619	$ 620,062
Sequoia Choice \| Restricted cash
Variable Interest Entity [Line Items]
Assets	7	4
Sequoia Choice \| Accrued interest receivable
Variable Interest Entity [Line Items]
Assets	4,057	2,524
Sequoia Choice \| REO
Variable Interest Entity [Line Items]
Assets	0	0
Sequoia Choice \| Accrued interest payable
Variable Interest Entity [Line Items]
Liabilities	3,438	2,031
Sequoia Choice \| Accrued expenses and other liabilities
Variable Interest Entity [Line Items]
Liabilities	7	4
Sequoia Choice \| Asset-backed securities issued
Variable Interest Entity [Line Items]
Liabilities	$ 926,238	$ 542,140

Number of Variable Interest Entities, Acquired and Consolidated

No definition available.

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

- Definition

The carrying amount of the consolidated Variable Interest Entity's assets included in the reporting entity's statement of financial position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (bb)
-URI http://asc.fasb.org/extlink&oid=64801991&loc=d3e5710-111685

+ Details

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

- Definition

The carrying amount of the consolidated Variable Interest Entity's liabilities included in the reporting entity's statement of financial position.

+ References

+ Details

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

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

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=rwt_SequoiaSecuritizationEntitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=rwt_ResidentialLoansHeldForInvestmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=rwt_RestrictedCashMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=rwt_InterestReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=us-gaap_RealEstateInvestmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=rwt_InterestPayableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=us-gaap_AccruedLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=rwt_LegacySequoiaSecuritizationEntitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=rwt_SequoiaChoiceSecuritizationEntitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: