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Real Estate Securities - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015 Investment	Mar. 31, 2014	Dec. 31, 2014 Investment
Investment Holdings [Line Items]
Trading securities	$ 106,837,000us-gaap_TradingSecurities		$ 111,606,000us-gaap_TradingSecurities
Trading securities acquired	23,000,000us-gaap_PaymentsToAcquireTradingSecuritiesHeldforinvestment
Trading securities sold	3,000,000us-gaap_ProceedsFromSaleOfTradingSecuritiesHeldforinvestment
Adjustment to valuation of trading securities	(14,359,000)us-gaap_IncreaseDecreaseInTradingSecurities	(4,277,000)us-gaap_IncreaseDecreaseInTradingSecurities
Available-for-sale securities purchased	10,000,000us-gaap_PaymentsToAcquireAvailableForSaleSecurities	74,000,000us-gaap_PaymentsToAcquireAvailableForSaleSecurities
Available-for-sale securities sold	91,000,000us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities	0us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities
Gross realized gains	4,306,000us-gaap_AvailableForSaleSecuritiesGrossRealizedGains	0us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
Number of AFS securities	274rwt_NumberOfAvailableForSaleSecurities		290rwt_NumberOfAvailableForSaleSecurities
Number of securities in unrealized loss position	29us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1		31us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1
Number of securities in a continuous unrealized loss position for twelve consecutive months or longer	8rwt_NumberOfSecuritiesContinuousUnrealizedLossPositionMoreThanTwelveMonths		10rwt_NumberOfSecuritiesContinuousUnrealizedLossPositionMoreThanTwelveMonths
Gross unrealized losses on AFS securities	3,000,000us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Income Statement, other-than-temporary impairments		113,000us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet
Maximum
Investment Holdings [Line Items]
Income Statement, other-than-temporary impairments	0us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet / us-gaap_RangeAxis = us-gaap_MaximumMember
Senior Securities
Investment Holdings [Line Items]
Trading securities	73,263,000us-gaap_TradingSecurities / us-gaap_InvestmentTypeAxis = rwt_SeniorSecuritiesMember		101,753,000us-gaap_TradingSecurities / us-gaap_InvestmentTypeAxis = rwt_SeniorSecuritiesMember
Interest Only Securities
Investment Holdings [Line Items]
Trading securities	70,000,000us-gaap_TradingSecurities / us-gaap_InvestmentTypeAxis = rwt_InterestOnlySecuritiesMember
Residential Senior and Subordinate Securities
Investment Holdings [Line Items]
Trading securities	4,000,000us-gaap_TradingSecurities / us-gaap_InvestmentTypeAxis = rwt_ResidentialSeniorSecuritiesMember
Residential Subordinate Securities
Investment Holdings [Line Items]
Trading securities	33,000,000us-gaap_TradingSecurities / us-gaap_InvestmentTypeAxis = rwt_ResidentialSubordinateSecuritiesMember
Trading Securities | Residential Senior and Subordinate Securities
Investment Holdings [Line Items]
Unpaid principal balance	4,000,000us-gaap_InvestmentOwnedBalancePrincipalAmount / invest_InvestmentSecuritiesClassAxis = rwt_TradingSecuritiesMember / us-gaap_InvestmentTypeAxis = rwt_ResidentialSeniorSecuritiesMember
Trading Securities | Residential Subordinate Securities
Investment Holdings [Line Items]
Unpaid principal balance	45,000,000us-gaap_InvestmentOwnedBalancePrincipalAmount / invest_InvestmentSecuritiesClassAxis = rwt_TradingSecuritiesMember / us-gaap_InvestmentTypeAxis = rwt_ResidentialSubordinateSecuritiesMember
Prime | Senior Securities
Investment Holdings [Line Items]
Trading securities	65,809,000us-gaap_TradingSecurities / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialPrimeFinancingReceivableMember / us-gaap_InvestmentTypeAxis = rwt_SeniorSecuritiesMember		93,802,000us-gaap_TradingSecurities / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialPrimeFinancingReceivableMember / us-gaap_InvestmentTypeAxis = rwt_SeniorSecuritiesMember
Securities financed through non-recourse resecuritization entity	98,000,000rwt_SecuritiesFinancedThroughNonrecourseResecuritization / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialPrimeFinancingReceivableMember / us-gaap_InvestmentTypeAxis = rwt_SeniorSecuritiesMember		105,000,000rwt_SecuritiesFinancedThroughNonrecourseResecuritization / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialPrimeFinancingReceivableMember / us-gaap_InvestmentTypeAxis = rwt_SeniorSecuritiesMember
Non-prime | Senior Securities
Investment Holdings [Line Items]
Trading securities	7,454,000us-gaap_TradingSecurities / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialSubprimeFinancingReceivableMember / us-gaap_InvestmentTypeAxis = rwt_SeniorSecuritiesMember		7,951,000us-gaap_TradingSecurities / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialSubprimeFinancingReceivableMember / us-gaap_InvestmentTypeAxis = rwt_SeniorSecuritiesMember
Securities financed through non-recourse resecuritization entity	113,000,000rwt_SecuritiesFinancedThroughNonrecourseResecuritization / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialSubprimeFinancingReceivableMember / us-gaap_InvestmentTypeAxis = rwt_SeniorSecuritiesMember		117,000,000rwt_SecuritiesFinancedThroughNonrecourseResecuritization / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialSubprimeFinancingReceivableMember / us-gaap_InvestmentTypeAxis = rwt_SeniorSecuritiesMember
Residential
Investment Holdings [Line Items]
Marketable securities, less than five years	7,000,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember
Marketable securities, due from five to ten years	$ 2,000,000us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost / invest_InvestmentSecuritiesClassAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember

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Securities Financed Through Nonrecourse Resecuritization

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

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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