Real Estate Securities - Components of Carrying Value (Which Equals Fair Value) of Residential Available for Sale Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	$ 971,013	$ 1,267,624
Senior Securities
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	409,313	487,557
Senior Securities \| Prime
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	251,273	307,813
Senior Securities \| Non-prime
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	158,040	179,744
Re-REMIC
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	167,639	168,347
Subordinate Securities
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	394,061	611,720
Subordinate Securities \| Prime
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	233,458	448,838
Subordinate Securities \| Non-prime
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	1,000	1,000
Residential
Schedule of Available-for-sale Securities [Line Items]
Principal balance	1,114,917	1,445,079
Credit reserve	(55,341)	(70,067)
Unamortized discount, net	(261,729)	(296,342)
Amortized cost	797,847	1,078,670
Gross unrealized gains	177,576	191,750
Gross unrealized losses	(4,410)	(2,796)
Carrying Value	971,013	1,267,624
Residential \| Senior Securities \| Prime
Schedule of Available-for-sale Securities [Line Items]
Principal balance	257,526	311,573
Credit reserve	(2,377)	(3,660)
Unamortized discount, net	(27,476)	(34,782)
Amortized cost	227,673	273,131
Gross unrealized gains	26,899	35,980
Gross unrealized losses	(3,299)	(1,298)
Carrying Value	251,273	307,813
Residential \| Senior Securities \| Non-prime
Schedule of Available-for-sale Securities [Line Items]
Principal balance	174,285	196,258
Credit reserve	(8,964)	(9,644)
Unamortized discount, net	(25,505)	(31,491)
Amortized cost	139,816	155,123
Gross unrealized gains	18,515	24,682
Gross unrealized losses	(291)	(61)
Carrying Value	158,040	179,744
Residential \| Re-REMIC
Schedule of Available-for-sale Securities [Line Items]
Principal balance	192,215	195,098
Credit reserve	(11,135)	(15,202)
Unamortized discount, net	(74,377)	(79,611)
Amortized cost	106,703	100,285
Gross unrealized gains	60,936	68,062
Gross unrealized losses	0	0
Carrying Value	167,639	168,347
Residential \| Subordinate Securities
Schedule of Available-for-sale Securities [Line Items]
Principal balance	490,891	742,150
Credit reserve	(32,865)	(41,561)
Unamortized discount, net	(134,371)	(150,458)
Amortized cost	323,655	550,131
Gross unrealized gains	71,226	63,026
Gross unrealized losses	(820)	(1,437)
Carrying Value	$ 394,061	$ 611,720

Balance of credit reserve on available-for-sale securities.

No definition available.

Name:	rwt_AvailableForSaleSecuritiesCreditReserve
Namespace Prefix:	rwt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Available For Sale Securities Principal Balance

+ References

No definition available.

+ Details

Name:	rwt_AvailableForSaleSecuritiesPrincipalBalance
Namespace Prefix:	rwt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Balance of net unamortized discount on available-for-sale securities.

+ References

No definition available.

+ Details

Name:	rwt_AvailableForSaleSecuritiesUnamortizedDiscountsPremiums
Namespace Prefix:	rwt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

+ Details

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

- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

+ Details

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

- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (aa)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26610-111562

+ Details

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

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAmortizedCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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_ScheduleOfAvailableForSaleSecuritiesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Details

Name:	invest_InvestmentSecuritiesClassAxis=rwt_RealEstateSecuritiesPrimeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	invest_InvestmentSecuritiesClassAxis=rwt_RealEstateSecuritiesSubprimeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: