Summary of Significant Accounting Policies - Offsetting of Financial Assets, Liabilities, and Collateral (Details) - USD ($) $ in Thousands		Sep. 30, 2019	Dec. 31, 2018
Assets
Net Amounts of Assets (Liabilities) Presented in Consolidated Balance Sheet	[1]	$ 43,649	$ 35,789
Liabilities
Net Amounts of Assets (Liabilities) Presented in Consolidated Balance Sheet	[1]	(234,011)	(84,855)
Total Liabilities
Gross Amounts of Recognized Assets (Liabilities)		(1,623,212)	(1,933,663)
Gross Amounts Offset in Consolidated Balance Sheet		0	0
Net Amounts of Assets (Liabilities) Presented in Consolidated Balance Sheet		(1,623,212)	(1,933,663)
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments		1,420,120	1,881,142
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received) Pledged		202,831	48,317
Net Amount		(261)	(4,204)
Interest rate agreements
Assets
Gross Amounts of Recognized Assets (Liabilities)		33,642	28,211
Gross Amounts Offset in Consolidated Balance Sheet		0	0
Net Amounts of Assets (Liabilities) Presented in Consolidated Balance Sheet		33,642	28,211
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments		(25,802)	(28,211)
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received) Pledged		(4,379)	0
Net Amount		3,461	0
Liabilities
Gross Amounts of Recognized Assets (Liabilities)		(228,150)	(70,908)
Gross Amounts Offset in Consolidated Balance Sheet		0	0
Net Amounts of Assets (Liabilities) Presented in Consolidated Balance Sheet		(228,150)	(70,908)
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments		25,802	28,211
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received) Pledged		202,348	42,697
Net Amount		0	0
TBAs
Assets
Gross Amounts of Recognized Assets (Liabilities)		5,250	4,665
Gross Amounts Offset in Consolidated Balance Sheet		0	0
Net Amounts of Assets (Liabilities) Presented in Consolidated Balance Sheet		5,250	4,665
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments		(3,448)	(3,391)
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received) Pledged		(1,040)	(835)
Net Amount		762	439
Liabilities
Gross Amounts of Recognized Assets (Liabilities)		(4,192)	(13,215)
Gross Amounts Offset in Consolidated Balance Sheet		0	0
Net Amounts of Assets (Liabilities) Presented in Consolidated Balance Sheet		(4,192)	(13,215)
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments		3,448	3,391
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received) Pledged		483	5,620
Net Amount		(261)	(4,204)
Interest Rate Agreement, TBAs, And Futures
Assets
Gross Amounts of Recognized Assets (Liabilities)		38,892	32,876
Net Amounts of Assets (Liabilities) Presented in Consolidated Balance Sheet		38,892	32,876
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments		(29,250)	(31,602)
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received) Pledged		(5,419)	(835)
Net Amount		4,223	439
Loan warehouse debt
Loan warehouse debt and Security repurchase agreement
Gross Amounts of Recognized Assets (Liabilities)		(233,224)	(860,650)
Gross Amounts Offset in Consolidated Balance Sheet		0	0
Net Amounts of Assets (Liabilities) Presented in Consolidated Balance Sheet		(233,224)	(860,650)
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments		233,224	860,650
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received) Pledged		0	0
Security repurchase agreements
Loan warehouse debt and Security repurchase agreement
Gross Amounts of Recognized Assets (Liabilities)		(1,157,646)	(988,890)
Gross Amounts Offset in Consolidated Balance Sheet		0	0
Net Amounts of Assets (Liabilities) Presented in Consolidated Balance Sheet		(1,157,646)	(988,890)
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments		1,157,646	988,890
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received) Pledged		0	0
Net Amount		$ 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 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.