Short-Term Debt - Outstanding Balances of Short-Term Debt by Type of Collateral Securing Debt (Details)		3 Months Ended	12 Months Ended
		Mar. 31, 2020 USD ($) facility	Dec. 31, 2019 USD ($) facility
Short-term Debt [Line Items]
Outstanding Balance	[1]	$ 2,341,648,000	$ 2,329,145,000
Facilities
Short-term Debt [Line Items]
Number of Facilities | facility		17	22
Outstanding Balance		$ 2,082,717,000	$ 2,176,591,000
Facilities | Residential loan warehouse
Short-term Debt [Line Items]
Number of Facilities | facility		4	4
Outstanding Balance		$ 841,186,000	$ 185,894,000
Limit		$ 1,525,000,000	$ 1,425,000,000
Weighted Average Interest Rate		2.38%	3.23%
Weighted Average Days Until Maturity		312 days	69 days
Facilities | Business purpose residential loan warehouse
Short-term Debt [Line Items]
Number of Facilities | facility		6	8
Outstanding Balance		$ 756,384,000	$ 814,118,000
Limit		$ 1,410,000,000	$ 1,475,000,000
Weighted Average Interest Rate		3.51%	4.11%
Weighted Average Days Until Maturity		404 days	489 days
Facilities | Real estate securities repo
Short-term Debt [Line Items]
Number of Facilities | facility		7	10
Outstanding Balance		$ 485,147,000	$ 1,176,579,000
Limit		$ 0	$ 0
Weighted Average Interest Rate		2.77%	2.94%
Weighted Average Days Until Maturity		32 days	23 days
Servicer advance financing
Short-term Debt [Line Items]
Number of Facilities | facility		1	1
Outstanding Balance		$ 258,931,000	$ 152,554,000
Limit		$ 400,000,000	$ 400,000,000
Weighted Average Interest Rate		2.57%	3.56%
Weighted Average Days Until Maturity		244 days	335 days

[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 March 31, 2020 and December 31, 2019, assets of consolidated VIEs totaled $7,470,706 and $11,931,869, respectively. At March 31, 2020 and December 31, 2019, liabilities of consolidated VIEs totaled $6,759,260 and $10,717,072, respectively. See Note 4 for further discussion.