Long-Term Debt - Additional Information (Details) - USD ($)		1 Months Ended				3 Months Ended	12 Months Ended
		Aug. 31, 2017	Jan. 31, 2016	Nov. 30, 2014	Mar. 31, 2013	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Committed line of credit with financial institutions, outstanding							$ 0	$ 0
FHLB transition period			5 years
Federal home loan bank stock							43,393,000	43,393,000
Accrued interest payable							2,000,000	1,000,000
Notional Amount							6,644,081,000	4,980,343,000
Accrued interest payable (less than)	[1]						18,435,000	9,608,000
Convertible notes | Senior Notes Due 2023
Debt Instrument [Line Items]
Convertible notes		$ 245,000,000					$ 245,000,000
Debt instrument interest rate		4.75%
Debt instrument, maturity year		2023
Net proceeds from issuance of convertible debt		$ 238,000,000
Interest expense yield							5.30%
Convertible debt, conversion ratio							0.0538394
Convertible senior notes conversion per share (in dollars per share)							$ 18.57
Accrued interest payable							$ 4,000,000
Unamortized deferred issuance costs							(7,000,000)
Convertible notes | Exchangeable senior notes due 2019
Debt Instrument [Line Items]
Convertible notes				$ 205,000,000			$ 201,000,000
Debt instrument interest rate				5.625%
Debt instrument, maturity year				2019
Net proceeds from issuance of convertible debt				$ 198,000,000
Interest expense yield							6.30%
Convertible debt, conversion ratio							0.0461798
Convertible senior notes conversion per share (in dollars per share)							$ 21.65
Accrued interest payable							$ 1,000,000
Unamortized deferred issuance costs							(2,000,000)
Debt instrument, redemption date				Nov. 15, 2019
Repurchased debt instrument, face amount							$ 0	4,000,000
Convertible notes | Exchangeable senior notes due 2019 | Gain (Loss) on Investments
Debt Instrument [Line Items]
Gain (loss) on extinguishment of debt								300,000
Convertible notes | Convertible senior notes due 2018
Debt Instrument [Line Items]
Convertible notes					$ 288,000,000	$ 288,000,000
Debt instrument interest rate					4.625%
Net proceeds from issuance of convertible debt					$ 279,000,000
Interest expense yield							4.80%
Convertible debt, conversion ratio							0.041132
Convertible senior notes conversion per share (in dollars per share)							$ 24.31
Accrued interest payable							$ 2,000,000
Unamortized deferred issuance costs							(200,000)
Repurchased debt instrument, face amount						37,000,000
Gain (loss) on extinguishment of debt						(1,000,000)
Deferred debt issuance costs						$ 2,000,000
Current maturities of long-term debt							250,000,000
Trust Preferred Securities
Debt Instrument [Line Items]
Debt instrument face amount							$ 100,000,000
Interest expense yield on trust preferred securities and subordinated notes							(6.90%)
Subordinated Notes
Debt Instrument [Line Items]
Debt instrument face amount							$ 40,000,000
Trust Preferred Securities and Subordinated Notes
Debt Instrument [Line Items]
Accrued interest payable (less than)							1,000,000	1,000,000
Trust Preferred Securities and Subordinated Notes | Interest rate agreements
Debt Instrument [Line Items]
Notional Amount							$ 140,000,000
Trust Preferred Securities and Subordinated Notes | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate							2.25%
FHLB Chicago | Redwood | Held-for sale residential loans
Debt Instrument [Line Items]
Residential mortgage loans securing FHLB advances							$ 2,430,000,000
Subsidiaries | FHLB Chicago
Debt Instrument [Line Items]
Maximum borrowing capacity							2,000,000,000
Additional borrowings from FHLB								519,000,000
Committed line of credit with financial institutions, outstanding							2,000,000,000
Outstanding FHLB advances							$ 2,000,000,000	$ 2,000,000,000
Weighted average interest rate							1.38%	0.64%
Weighted average maturity (in years)							8 years	9 years

[1] Our consolidated balance sheets include assets of consolidated variable interest entities (“VIEs”) that can only be used to settle obligations of these VIEs and liabilities of consolidated VIEs for which creditors do not have recourse to Redwood Trust, Inc. or its affiliates. At December 31, 2017 and December 31, 2016, assets of consolidated VIEs totaled $1,259,774 and $798,317, respectively. At December 31, 2017 and December 31, 2016, liabilities of consolidated VIEs totaled $1,167,157 and $773,980, respectively. See Note 4 for further discussion.