Equity Compensation Plans - Unrecognized Compensation Cost (Details) $ in Thousands	6 Months Ended
Jun. 30, 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	10,254
Performance-based valuation adjustment	(7,352)
Equity grant forfeitures	(6,996)
Equity compensation expense	(5,257)
Unrecognized Compensation Cost at End of Period	22,977
Redwood Incentive Plan \| 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	70
Performance-based valuation adjustment	0
Equity grant forfeitures	(349)
Equity compensation expense	(614)
Unrecognized Compensation Cost at End of Period	1,097
Redwood Incentive Plan \| 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	3,431
Performance-based valuation adjustment	0
Equity grant forfeitures	(1,266)
Equity compensation expense	(772)
Unrecognized Compensation Cost at End of Period	4,927
Redwood Incentive Plan \| 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	6,593
Performance-based valuation adjustment	0
Equity grant forfeitures	(4,733)
Equity compensation expense	(4,511)
Unrecognized Compensation Cost at End of Period	15,207
Redwood Incentive Plan \| 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	(648)
Equity compensation expense	720
Unrecognized Compensation Cost at End of Period	1,666
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	(80)
Unrecognized Compensation Cost at End of Period	$ 80

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=120381028&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=120381028&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_RedwoodIncentivePlanMember
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: