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Long-Term Debt - Additional Information (Details)			1 Months Ended				3 Months Ended	6 Months Ended	12 Months Ended
		Dec. 31, 2018 USD ($)	Jun. 30, 2018 USD ($) $ / shares	Aug. 31, 2017 USD ($) $ / shares	Jan. 31, 2016	Nov. 30, 2014 USD ($) $ / shares	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2016 USD ($)	Nov. 15, 2018 USD ($)	Dec. 31, 2013 USD ($)
Debt Instrument [Line Items]
Transition period for subsidiary to be a FHLB-member (in years)					5 years
Existing debt		$ 0					$ 0	$ 0
Federal home loan bank stock		43,393,000					43,393,000	43,393,000
Accrued interest payable		4,000,000					5,000,000	5,000,000
Convertible notes										$ 201,000,000
Debt instrument face amount	[1]	2,572,158,000					2,573,173,000	2,573,173,000
Notional amount		5,911,385,000					7,597,742,000	7,597,742,000
Accrued interest payable	[1]	42,528,000					47,092,000	47,092,000
Trust Preferred Securities
Debt Instrument [Line Items]
Debt instrument face amount							100,000,000	100,000,000
Subordinated Notes
Debt Instrument [Line Items]
Debt instrument face amount							$ 40,000,000	$ 40,000,000
Trust Preferred Securities And Subordinated Notes
Debt Instrument [Line Items]
Weighted average interest rates, by series							6.90%	6.90%
Accrued interest payable		$ 1,000,000					$ 1,000,000	$ 1,000,000
Trust Preferred Securities And Subordinated Notes | Interest rate swaps
Debt Instrument [Line Items]
Notional amount											$ 140,000,000
Trust Preferred Securities And Subordinated Notes | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate								2.25%
Senior Notes Due 2024 | Convertible Debt
Debt Instrument [Line Items]
Convertible notes			$ 200,000,000				200,000,000	$ 200,000,000
Debt Instrument interest rate			5.625%
Debt instrument, percent of par			99.50%
Net proceeds from issuance of convertible debt			$ 194,000,000
Interest expense yield								6.20%
Convertible senior notes conversion rate								0.0547645
Convertible senior notes conversion per share (in dollars per share) | $ / shares			$ 18.26
Accrued interest payable							5,000,000	$ 5,000,000
Unamortized debt issuance costs							4,000,000	4,000,000
Unamortized discount							1,000,000	1,000,000
Senior Notes Due 2023 | Convertible Debt
Debt Instrument [Line Items]
Convertible notes				$ 245,000,000			245,000,000	$ 245,000,000
Debt Instrument interest rate				4.75%
Net proceeds from issuance of convertible debt				$ 238,000,000
Interest expense yield				5.30%
Convertible senior notes conversion rate								0.0539060
Convertible senior notes conversion per share (in dollars per share) | $ / shares				$ 18.55
Accrued interest payable							4,000,000	$ 4,000,000
Unamortized debt issuance costs							5,000,000	5,000,000
Exchangeable Senior Notes Due 2019 | Convertible Debt
Debt Instrument [Line Items]
Convertible notes						$ 205,000,000	201,000,000	$ 201,000,000
Debt Instrument interest rate		5.625%				5.625%
Net proceeds from issuance of convertible debt						$ 198,000,000
Interest expense yield						6.30%
Convertible senior notes conversion rate								0.0462370
Convertible senior notes conversion per share (in dollars per share) | $ / shares						$ 21.63
Accrued interest payable							1,000,000	$ 1,000,000
Unamortized debt issuance costs							1,000,000	$ 1,000,000
Amount of debt repurchased									$ 4,000,000
Unamortized deferred issuance costs		$ 1,000,000
Exchangeable Senior Notes Due 2019 | Convertible Debt | Gain (loss) on investments
Debt Instrument [Line Items]
Gain on extinguishment of debt									$ 300,000
FHLB Chicago
Debt Instrument [Line Items]
Interest rate margin reset period								91 days
FHLB Chicago | FHLB Member Subsidiary
Debt Instrument [Line Items]
Maximum borrowing limit							2,000,000,000.00	$ 2,000,000,000.00
Additional borrowings from FHLBC							0	0
Existing debt							2,000,000,000.00	2,000,000,000.00
Federal home loan bank advances outstanding		$ 2,000,000,000.00					$ 2,000,000,000.00	$ 2,000,000,000.00
Weighted average interest rate		2.52%					2.57%	2.57%
Weighted average maturity (in years)		7 years						6 years
Debt instrument face amount							$ 1,999,999,000	$ 1,999,999,000
FHLB Chicago | Redwood | Held-for-sale residential loans | Residential Real Estate
Debt Instrument [Line Items]
Loans pledged as collateral under borrowing agreement with FHLBC							$ 2,390,000,000	$ 2,390,000,000
[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 June 30, 2019 and December 31, 2018, assets of consolidated VIEs totaled $7,937,685 and $6,331,191, respectively. At June 30, 2019 and December 31, 2018, liabilities of consolidated VIEs totaled $7,189,086 and $5,709,807, respectively. See Note 4 for further discussion.

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