Mortgage Banking and Investment Activities, Net - Components of Mortgage Banking Activities (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Mortgage Loans on Real Estate [Line Items]
Hedging allocation	$ 0		$ 0
Total investment activities	(14,169)	$ (3,749)	(17,105)	$ (14,020)
Mortgage banking and investment activities	(12,836)	14,166	(6,399)	9,984
Residential Mortgage Banking Activities
Mortgage Loans on Real Estate [Line Items]
Other income	1,177	1,082	3,209	1,871
Mortgage banking activities	331	11,429	7,383	11,704
Hedging allocation	(1,683)	0	1,120	0
Residential Mortgage Banking Activities \| Residential loans, at fair value
Mortgage Loans on Real Estate [Line Items]
Changes in fair value of assets	36,183	15,976	54,375	40,685
Residential Mortgage Banking Activities \| Real estate securities
Mortgage Loans on Real Estate [Line Items]
Changes in fair value of assets	0	(1,332)	(14,359)	(14,419)
Residential Mortgage Banking Activities \| Risk managment derivatives
Mortgage Loans on Real Estate [Line Items]
Changes in fair value of risk management derivatives	(35,346)	(4,297)	(36,962)	(16,433)
Commercial Mortgage Banking Activities
Mortgage Loans on Real Estate [Line Items]
Other income	109	289	336	382
Mortgage banking activities	1,002	6,486	3,323	12,300
Commercial Mortgage Banking Activities \| Risk managment derivatives
Mortgage Loans on Real Estate [Line Items]
Changes in fair value of risk management derivatives	(3,081)	1,892	(7,832)	(1,726)
Commercial Mortgage Banking Activities \| Commercial loans, at fair value
Mortgage Loans on Real Estate [Line Items]
Changes in fair value of assets	3,974	4,305	10,819	13,644
Investment Activities
Mortgage Loans on Real Estate [Line Items]
Changes in fair value of risk management derivatives	(14,321)	(1,632)	(15,266)	(10,986)
Hedging allocation	1,683	0	(1,120)	0
Investment Activities \| Real estate securities
Mortgage Loans on Real Estate [Line Items]
Changes in fair value of assets	(9,010)	(765)	(1,813)	(1,218)
Investment Activities \| Net investments in consolidated Sequoia entities
Mortgage Loans on Real Estate [Line Items]
Changes in fair value of assets	(500)	(361)	(2,277)	(825)
Investment Activities \| Residential loans held-for-investment, at Redwood
Mortgage Loans on Real Estate [Line Items]
Changes in fair value of assets	9,077	(991)	5,170	(991)
Investment Activities \| Risk sharing investments
Mortgage Loans on Real Estate [Line Items]
Changes in fair value of assets	$ (1,098)	$ 0	$ (1,799)	$ 0

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

Investment Banking Activities, Net

+ References

No definition available.

+ Details

Name:	rwt_InvestmentBankingActivitiesNet
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

Mortgage Banking And Investment Activities

+ References

No definition available.

+ Details

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

- Definition

Fee and commission revenue earned from sources not otherwise specified in the existing taxonomy.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.13)

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

+ Details

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

- Definition

Gain (loss) incurred in hedging activities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5618551-113959

+ Details

Name:	us-gaap_GainLossOnOilAndGasHedgingActivity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4C

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624171-113959

+ Details

Name:	us-gaap_IncreaseDecreaseInFairValueOfPriceRiskFairValueHedgingInstruments1
Namespace Prefix:	us-gaap_
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:	us-gaap_MortgageLoansOnRealEstateLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
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=rwt_RealEstateSecuritiesMember
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_CommercialMortgageBankingActivitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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