Long-Term Debt - Additional Information (Details)				1 Months Ended					3 Months Ended	9 Months Ended	12 Months Ended
		Sep. 30, 2019 USD ($) $ / shares	Dec. 31, 2018 USD ($)	Sep. 30, 2019 USD ($) $ / shares	Jun. 30, 2018 USD ($) $ / shares	Aug. 31, 2017 USD ($) $ / shares	Jan. 31, 2016	Nov. 30, 2014 USD ($) $ / shares	Sep. 30, 2019 USD ($) $ / shares	Sep. 30, 2019 USD ($) $ / shares	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					$ 0	$ 0
Federal home loan bank stock		43,393,000	43,393,000	43,393,000					43,393,000	43,393,000
Debt instrument face amount	[1]	2,953,722,000	2,572,158,000	2,953,722,000					2,953,722,000	2,953,722,000
Accrued interest payable		3,000,000	4,000,000	3,000,000					3,000,000	3,000,000
Convertible notes												$ 201,000,000
Notional amount		10,799,279,000	5,911,385,000	10,799,279,000					10,799,279,000	10,799,279,000
Accrued interest payable	[1]	$ 46,881,000	$ 42,528,000	$ 46,881,000					$ 46,881,000	$ 46,881,000
Convertible Debt | Exchangeable Senior Notes Due 2025
Debt Instrument [Line Items]
Debt Instrument interest rate		5.75%		5.75%					5.75%	5.75%
Unamortized debt issuance costs		$ 6,000,000		$ 6,000,000					$ 6,000,000	$ 6,000,000
Convertible notes		$ 201,000,000		201,000,000					$ 201,000,000	$ 201,000,000
Net proceeds from issuance of convertible debt				$ 195,000,000
Interest expense yield				6.30%
Convertible senior notes conversion per share (in dollars per share) | $ / shares		$ 18.12		$ 18.12					$ 18.12	$ 18.12
Accrued interest payable		$ 200,000		$ 200,000					$ 200,000	$ 200,000
Convertible Debt | Senior Notes Due 2024
Debt Instrument [Line Items]
Debt Instrument interest rate					5.625%
Unamortized debt issuance costs		4,000,000		4,000,000					4,000,000	4,000,000
Convertible notes		200,000,000		200,000,000	$ 200,000,000				200,000,000	$ 200,000,000
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		2,000,000		2,000,000					2,000,000	$ 2,000,000
Debt instrument, percent of par					99.50%
Unamortized discount		1,000,000		1,000,000					1,000,000	1,000,000
Convertible Debt | Senior Notes Due 2023
Debt Instrument [Line Items]
Debt Instrument interest rate						4.75%
Unamortized debt issuance costs		5,000,000		5,000,000					5,000,000	5,000,000
Convertible notes		245,000,000		245,000,000		$ 245,000,000			245,000,000	$ 245,000,000
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		1,000,000		1,000,000					1,000,000	$ 1,000,000
Convertible Debt | Exchangeable Senior Notes Due 2019
Debt Instrument [Line Items]
Debt Instrument interest rate			5.625%					5.625%
Unamortized debt issuance costs		200,000		200,000					200,000	200,000
Convertible notes		201,000,000		201,000,000				$ 205,000,000	201,000,000	$ 201,000,000
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		4,000,000		4,000,000					4,000,000	$ 4,000,000
Amount of debt repurchased											$ 4,000,000
Unamortized deferred issuance costs			$ 1,000,000
Convertible Debt | Exchangeable Senior Notes Due 2019 | Gain (loss) on investments
Debt Instrument [Line Items]
Gain on extinguishment of debt											$ 300,000
Trust Preferred Securities
Debt Instrument [Line Items]
Debt instrument face amount		100,000,000		100,000,000					100,000,000	100,000,000
Subordinated Notes
Debt Instrument [Line Items]
Debt instrument face amount		$ 40,000,000		$ 40,000,000					$ 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%					6.90%	6.90%
Accrued interest payable		$ 1,000,000	1,000,000	$ 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%
Affiliated Entity | Long Term Non Market To market Recourse Debt Financing
Debt Instrument [Line Items]
Debt Instrument interest rate					4.21%
Amount outstanding		186,000,000		186,000,000					186,000,000	$ 186,000,000
Unamortized debt issuance costs		1,000,000		1,000,000					1,000,000	1,000,000
Debt instrument face amount		185,000,000		185,000,000					185,000,000	185,000,000
Pledged assets real estate pledged as collateral, at fair value		253,000,000		253,000,000					253,000,000	253,000,000
Affiliated Entity | Sequoia Choice | Long Term Non Market To market Recourse Debt Financing
Debt Instrument [Line Items]
Pledged assets real estate pledged as collateral, at fair value		126,000,000		126,000,000					126,000,000	$ 126,000,000
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					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					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					$ 2,000,000,000.00	$ 2,000,000,000.00
Weighted average interest rate		2.31%	2.52%	2.31%					2.31%	2.31%
Weighted average maturity (in years)		6 years	7 years
Debt instrument face amount		$ 1,999,999,000		$ 1,999,999,000					$ 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		2,270,000,000		2,270,000,000					2,270,000,000	2,270,000,000
FHLB Chicago | Redwood | Held-for-sale residential loans | Securities
Debt Instrument [Line Items]
Loans pledged as collateral under borrowing agreement with FHLBC		41,000,000		41,000,000					41,000,000	41,000,000
FHLB Chicago | Redwood | Held-for-sale residential loans | Restricted cash
Debt Instrument [Line Items]
Loans pledged as collateral under borrowing agreement with FHLBC		$ 77,000,000		$ 77,000,000					$ 77,000,000	$ 77,000,000

[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 September 30, 2019 and December 31, 2018, assets of consolidated VIEs totaled $9,596,537 and $6,331,191, respectively. At September 30, 2019 and December 31, 2018, liabilities of consolidated VIEs totaled $8,582,595 and $5,709,807, respectively. See Note 4 for further discussion.