Summary of Significant Accounting Policies - Offsetting of Financial Assets, Liabilities, and Collateral (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Offsetting Asset and Liabilities [Line Items]
Derivative assets	[1]	$ 35,789	$ 15,718
Gross Amounts of Recognized Liabilities		(1,933,663)	(1,747,787)
Gross Amounts Offset in Consolidated Balance Sheet		0	0
Net Amounts of Liabilities Presented in Consolidated Balance Sheet - Derivatives	[1]	(84,855)	(63,081)
Net Amounts of Liabilities Presented in Consolidated Balance Sheet		(1,933,663)	(1,747,787)
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments		1,881,142	1,694,741
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral Pledged		48,317	50,747
Net Amount		(4,204)	(2,299)
Interest Rate Agreement, TBAs, And Futures
Offsetting Asset and Liabilities [Line Items]
Gross Amounts of Recognized Assets		32,876	10,298
Gross Amounts Offset in Consolidated Balance Sheet		0	0
Derivative assets		32,876	10,298
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments		(31,602)	(6,329)
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral Received		(835)	(42)
Net Amount		439	3,927
Interest rate agreements
Offsetting Asset and Liabilities [Line Items]
Gross Amounts of Recognized Assets		28,211	10,164
Gross Amounts Offset in Consolidated Balance Sheet		0	0
Derivative assets		28,211	10,164
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments		(28,211)	(6,196)
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral Received		0	(42)
Net Amount		0	3,926
Gross Amounts of Recognized Liabilities - Derivatives		(70,908)	(55,567)
Gross Amounts Offset in Consolidated Balance Sheet - Derivatives		0	0
Net Amounts of Liabilities Presented in Consolidated Balance Sheet - Derivatives		(70,908)	(55,567)
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments - Derivatives		28,211	6,196
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral Pledged - Derivatives		42,697	49,371
Net Amount - Derivatives		0	0
TBAs
Offsetting Asset and Liabilities [Line Items]
Gross Amounts of Recognized Assets		4,665	133
Gross Amounts Offset in Consolidated Balance Sheet		0	0
Derivative assets		4,665	133
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments		(3,391)	(133)
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral Received		(835)	0
Net Amount		439	0
Gross Amounts of Recognized Liabilities - Derivatives		(13,215)	(3,808)
Gross Amounts Offset in Consolidated Balance Sheet - Derivatives		0	0
Net Amounts of Liabilities Presented in Consolidated Balance Sheet - Derivatives		(13,215)	(3,808)
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments - Derivatives		3,391	133
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral Pledged - Derivatives		5,620	1,376
Net Amount - Derivatives		(4,204)	(2,299)
Futures
Offsetting Asset and Liabilities [Line Items]
Gross Amounts of Recognized Assets			1
Gross Amounts Offset in Consolidated Balance Sheet			0
Derivative assets			1
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments			0
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral Received			0
Net Amount			1
Loan warehouse debt
Offsetting Asset and Liabilities [Line Items]
Gross Amounts of Recognized Liabilities - Other		(860,650)	(1,039,666)
Gross Amounts Offset in Consolidated Balance Sheet - Other		0	0
Net Amounts of Liabilities Presented in Consolidated Balance Sheet - Other		(860,650)	(1,039,666)
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments - Other		860,650	1,039,666
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral Pledged - Other		0	0
Net Amount - Other		0	0
Security repurchase agreements
Offsetting Asset and Liabilities [Line Items]
Gross Amounts of Recognized Liabilities - Other		(988,890)	(648,746)
Gross Amounts Offset in Consolidated Balance Sheet - Other		0	0
Net Amounts of Liabilities Presented in Consolidated Balance Sheet - Other		(988,890)	(648,746)
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments - Other		988,890	648,746
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral Pledged - Other		0	0
Net Amount - Other		$ 0	$ 0

[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, 2018 and December 31, 2017, assets of consolidated VIEs totaled $6,331,191 and $1,259,774, respectively. At December 31, 2018 and December 31, 2017, liabilities of consolidated VIEs totaled $5,709,807 and $1,167,157, respectively. See Note 4 for further discussion.