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Changes of Unamortized Discount and Designated Credit Reserves on Residential Available for Sale Securities (Detail) (Residential, USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Residential
    
Credit Reserve    
Beginning balance $ 116,870rwt_AvailableForSaleSecuritiesCreditReserve
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 $ 187,032rwt_AvailableForSaleSecuritiesCreditReserve
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Amortization of net discount 0rwt_AvailableForSaleSecuritiesCreditReserveAmortizationOfNetDiscountPremium
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 0rwt_AvailableForSaleSecuritiesCreditReserveAmortizationOfNetDiscountPremium
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Realized credit losses (11,501)rwt_AvailableForSaleSecuritiesCreditReserveRealizedCreditGainsLosses
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 (21,971)rwt_AvailableForSaleSecuritiesCreditReserveRealizedCreditGainsLosses
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Acquisitions 3,581rwt_AvailableForSaleSecuritiesCreditReserveAcquisitions
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 13,604rwt_AvailableForSaleSecuritiesCreditReserveAcquisitions
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Sales, calls, other (2,555)rwt_AvailableForSaleSecuritiesCreditReserveSalesCallsOther
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 (19,868)rwt_AvailableForSaleSecuritiesCreditReserveSalesCallsOther
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Impairments 565rwt_AvailableForSaleSecuritiesCreditReserveImpairments
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 1,834rwt_AvailableForSaleSecuritiesCreditReserveImpairments
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Transfers to (release of) credit reserves, net (36,893)rwt_AvailableForSaleSecuritiesCreditReserveTransfersToReleaseOfCreditReserves
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 (43,761)rwt_AvailableForSaleSecuritiesCreditReserveTransfersToReleaseOfCreditReserves
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Ending Balance 70,067rwt_AvailableForSaleSecuritiesCreditReserve
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 116,870rwt_AvailableForSaleSecuritiesCreditReserve
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Unamortized Discount Net    
Beginning balance 298,469rwt_AvailableForSaleSecuritiesUnamortizedDiscountsPremiums
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 203,421rwt_AvailableForSaleSecuritiesUnamortizedDiscountsPremiums
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Amortization of net discount (42,835)rwt_AvailableForSaleSecuritiesUnamortizedDiscountsPremiumsAmortizationOfNetDiscountPremium
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 (34,943)rwt_AvailableForSaleSecuritiesUnamortizedDiscountsPremiumsAmortizationOfNetDiscountPremium
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Realized credit losses 0rwt_AvailableForSaleSecuritiesUnamortizedDiscountsPremiumsRealizedCreditGainsLosses
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 0rwt_AvailableForSaleSecuritiesUnamortizedDiscountsPremiumsRealizedCreditGainsLosses
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Acquisitions 15,348rwt_AvailableForSaleSecuritiesUnamortizedDiscountsPremiumsAcquisitions
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 92,124rwt_AvailableForSaleSecuritiesUnamortizedDiscountsPremiumsAcquisitions
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Sales, calls, other (11,533)rwt_AvailableForSaleSecuritiesUnamortizedDiscountsPremiumsSalesCallsOther
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 (5,894)rwt_AvailableForSaleSecuritiesUnamortizedDiscountsPremiumsSalesCallsOther
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Impairments 0rwt_AvailableForSaleSecuritiesUnamortizedDiscountsPremiumsImpairments
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 0rwt_AvailableForSaleSecuritiesUnamortizedDiscountsPremiumsImpairments
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Transfers to (release of) credit reserves, net 36,893rwt_AvailableForSaleSecuritiesUnamortizedDiscountsPremiumsTransfersToReleaseOfCreditReserves
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 43,761rwt_AvailableForSaleSecuritiesUnamortizedDiscountsPremiumsTransfersToReleaseOfCreditReserves
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
Ending Balance $ 296,342rwt_AvailableForSaleSecuritiesUnamortizedDiscountsPremiums
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 $ 298,469rwt_AvailableForSaleSecuritiesUnamortizedDiscountsPremiums
/ invest_InvestmentSecuritiesClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember