Mortgage Banking Activities, Net - Components of Mortgage Banking Activities (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Other income, net	$ (114)	$ 4,356	$ 3,979	$ 13,840
Mortgage banking activities, net	59,395	9,515	24,511	40,984
Residential Mortgage Banking Activities, Net
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Other income, net	(715)	407	(7,069)	1,380
Mortgage banking activities, net	11,864	5,017	(19,222)	31,203
Residential Mortgage Banking Activities, Net \| Residential loans, at fair value
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Changes in fair value of assets	12,589	6,320	19,151	41,431
Residential Mortgage Banking Activities, Net \| Risk management derivatives
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Risk management derivatives	(10)	(1,710)	(31,304)	(11,608)
Business Purpose Mortgage Banking Activities, Net:
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Changes in fair value of assets	938	1,010	(4,256)	2,108
Other income, net	3,491	2,903	13,407	5,979
Mortgage banking activities, net	47,531	4,498	43,733	9,781
Business Purpose Mortgage Banking Activities, Net: \| Risk management derivatives
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Risk management derivatives	(89)	(1,262)	(21,627)	(3,779)
Business Purpose Mortgage Banking Activities, Net: \| Single-family rental loans, at fair value
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Changes in fair value of assets	$ 43,191	$ 1,847	$ 56,209	$ 5,473

Increase (Decrease) in Fair Value Adjustments on Assets

No definition available.

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

- Definition

The net income attributable to mortgage banking activities. This includes market valuations related to residential and commercial loans, Sequoia IOs, and mortgage banking derivatives, as well as realized gains or losses associated with mortgage loan sales.

+ References

No definition available.

+ Details

Name:	rwt_MortgageBankingActivitiesNet
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

Amount of unrealized gain (loss) related to the fair value of price risk derivatives designated as fair value hedging instruments, as offset by the gain (loss) on the hedged item to the extent that the fair value hedge is determined to be effective.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5624171-113959

+ Details

Name:	us-gaap_IncreaseDecreaseInFairValueOfPriceRiskFairValueHedgingInstruments1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of revenue and income classified as other.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.4)
-URI http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

+ Details

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

- Details

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

- Details

Name:	us-gaap_FairValueByAssetClassAxis=rwt_ResidentialLoansAtFairValueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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