Summary of Significant Accounting Policies - Offsetting of Financial Assets, Liabilities, and Collateral (Details) - USD ($) $ in Thousands		Sep. 30, 2020	Dec. 31, 2019
Total Liabilities
Gross Amounts of Recognized Assets (Liabilities)		$ (157,230)	$ (1,690,828)
Gross Amounts Offset in Consolidated Balance Sheet		0	0
Net Amounts of Assets (Liabilities) Presented in Consolidated Balance Sheet		(157,230)	(1,690,828)
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments		156,967	1,548,637
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received) Pledged		263	141,260
Net Amount		0	(931)
Net Amounts of Assets (Liabilities) Presented in Consolidated Balance Sheet	[1]	(1,612)	(163,424)
Assets
Net Amounts of Assets (Liabilities) Presented in Consolidated Balance Sheet	[1]	14,709	35,701
Interest rate agreements
Total Liabilities
Gross Amounts of Recognized Assets (Liabilities)		(15)	(148,765)
Gross Amounts Offset in Consolidated Balance Sheet		0	0
Net Amounts of Assets (Liabilities) Presented in Consolidated Balance Sheet		(15)	(148,765)
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments		15	14,178
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received) Pledged		0	134,587
Net Amount		0	0
Assets
Gross Amounts of Recognized Assets (Liabilities)		3,471	19,020
Gross Amounts Offset in Consolidated Balance Sheet		0	0
Net Amounts of Assets (Liabilities) Presented in Consolidated Balance Sheet		3,471	19,020
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments		(15)	(14,178)
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received) Pledged		(1,240)	(915)
Net Amount		2,216	3,927
TBAs
Total Liabilities
Gross Amounts of Recognized Assets (Liabilities)		(263)	(13,359)
Gross Amounts Offset in Consolidated Balance Sheet		0	0
Net Amounts of Assets (Liabilities) Presented in Consolidated Balance Sheet		(263)	(13,359)
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments		0	5,755
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received) Pledged		263	6,673
Net Amount		0	(931)
Assets
Gross Amounts of Recognized Assets (Liabilities)		402	5,755
Gross Amounts Offset in Consolidated Balance Sheet		0	0
Net Amounts of Assets (Liabilities) Presented in Consolidated Balance Sheet		402	5,755
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments		0	(5,755)
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received) Pledged		(263)	0
Net Amount		139	0
Futures
Assets
Gross Amounts of Recognized Assets (Liabilities)		63	137
Gross Amounts Offset in Consolidated Balance Sheet		0	0
Net Amounts of Assets (Liabilities) Presented in Consolidated Balance Sheet		63	137
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments		0	0
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received) Pledged		0	0
Net Amount		63	137
Interest Rate Agreement, TBAs, and Futures
Assets
Gross Amounts of Recognized Assets (Liabilities)		3,936	24,912
Gross Amounts Offset in Consolidated Balance Sheet			0
Net Amounts of Assets (Liabilities) Presented in Consolidated Balance Sheet		3,936	24,912
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments		(15)	(19,933)
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received) Pledged		(1,503)	(915)
Net Amount		2,418	4,064
Loan warehouse debt
Loan warehouse debt and Security repurchase agreement
Gross Amounts of Recognized Assets (Liabilities)		(81,898)	(432,126)
Gross Amounts Offset in Consolidated Balance Sheet		0	0
Net Amounts of Assets (Liabilities) Presented in Consolidated Balance Sheet		(81,898)	(432,126)
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments		81,898	432,126
Gross Amounts Not Offset in Consolidated Balance Sheet, Cash Collateral (Received) Pledged		0	0
Net Amount			0
Security repurchase agreements
Loan warehouse debt and Security repurchase agreement
Gross Amounts of Recognized Assets (Liabilities)		(75,054)	(1,096,578)
Gross Amounts Offset in Consolidated Balance Sheet		0	0
Net Amounts of Assets (Liabilities) Presented in Consolidated Balance Sheet		(75,054)	(1,096,578)
Gross Amounts Not Offset in Consolidated Balance Sheet, Financial Instruments		75,054	1,096,578
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, 2020 and December 31, 2019, assets of consolidated VIEs totaled $8,197,095 and $11,931,869, respectively. At September 30, 2020 and December 31, 2019, liabilities of consolidated VIEs totaled $7,238,047 and $10,717,072, respectively. See Note 4 for further discussion.