Equity Compensation Plans - Unrecognized Compensation Cost (Details) $ in Thousands	3 Months Ended
Mar. 31, 2020 USD ($)
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized [Roll Forward]
Unrecognized compensation cost at beginning of period	$ 32,328
Equity grants	8,997
Performance-based valuation adjustment	(7,352)
Equity grant forfeitures	(138)
Equity compensation expense	(1,995)
Unrecognized Compensation Cost at End of Period	31,840
Incentive Plans \| Restricted Stock Awards
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized [Roll Forward]
Unrecognized compensation cost at beginning of period	1,990
Equity grants	5
Performance-based valuation adjustment	0
Equity grant forfeitures	(24)
Equity compensation expense	(344)
Unrecognized Compensation Cost at End of Period	1,627
Incentive Plans \| Restricted Stock Units
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized [Roll Forward]
Unrecognized compensation cost at beginning of period	3,534
Equity grants	3,352
Performance-based valuation adjustment	0
Equity grant forfeitures	(114)
Equity compensation expense	(347)
Unrecognized Compensation Cost at End of Period	6,425
Incentive Plans \| Deferred Stock Units
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized [Roll Forward]
Unrecognized compensation cost at beginning of period	17,858
Equity grants	5,480
Performance-based valuation adjustment	0
Equity grant forfeitures	0
Equity compensation expense	(1,993)
Unrecognized Compensation Cost at End of Period	21,345
Incentive Plans \| Performance Stock Units
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized [Roll Forward]
Unrecognized compensation cost at beginning of period	8,946
Equity grants	0
Performance-based valuation adjustment	(7,352)
Equity grant forfeitures	0
Equity compensation expense	729
Unrecognized Compensation Cost at End of Period	2,323
Employee Stock Purchase Plan
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized [Roll Forward]
Unrecognized compensation cost at beginning of period	0
Equity grants	160
Performance-based valuation adjustment	0
Equity grant forfeitures	0
Equity compensation expense	(40)
Unrecognized Compensation Cost at End of Period	$ 120

Allocated Share-based Compensation Expense, Including Restructuring

No definition available.

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

- Definition

Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized [Roll Forward]

+ References

No definition available.

+ Details

Name:	rwt_EmployeeServiceSharebasedCompensationNonvestedAwardsCompensationCostNotyetRecognizedRollForward
Namespace Prefix:	rwt_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the amount of equity grant forfeitures during the period.

+ References

No definition available.

+ Details

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

- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Valuation Adjustment

+ References

No definition available.

+ Details

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

- Definition

Amount of cost capitalized for award under share-based payment arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

+ Details

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

- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

+ Details

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

- Details

Name:	us-gaap_PlanNameAxis=rwt_IncentivePlansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=rwt_DeferredStockUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_PerformanceSharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=rwt_EmployeeStockPurchasePlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: