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Business Purpose Residential Loans - Geographic Concentration of Business Purpose Loans (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Single-family rental loans, held-for-sale at fair value
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	100.00%	100.00%
Single-family rental loans, held-for-sale at fair value | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	5.00%	69.00%
Single-family rental loans, held-for-sale at fair value | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	19.00%	14.00%
Single-family rental loans, held-for-sale at fair value | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	12.00%
Single-family rental loans, held-for-sale at fair value | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	5.00%
Single-family rental loans, held-for-sale at fair value | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	2.00%	0.00%
Single-family rental loans, held-for-sale at fair value | Utah
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	0.00%	0.00%
Single-family rental loans, held-for-sale at fair value | Georgia
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	8.00%
Single-family rental loans, held-for-sale at fair value | Alabama
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	5.00%
Single-family rental loans, held-for-sale at fair value | Arkansas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	6.00%
Single-family rental loans, held-for-sale at fair value | Maryland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	6.00%
Single-family rental loans, held-for-sale at fair value | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	1.00%
Single-family rental loans, held-for-sale at fair value | Other states (none greater than 5%)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	31.00%	17.00%
Residential bridge loans held-for-investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	100.00%	100.00%
Residential bridge loans held-for-investment | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	9.00%	7.00%
Residential bridge loans held-for-investment | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	3.00%	0.00%
Residential bridge loans held-for-investment | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	8.00%
Residential bridge loans held-for-investment | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	6.00%
Residential bridge loans held-for-investment | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	21.00%	79.00%
Residential bridge loans held-for-investment | Utah
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	5.00%	5.00%
Residential bridge loans held-for-investment | Georgia
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	7.00%
Residential bridge loans held-for-investment | Alabama
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	4.00%
Residential bridge loans held-for-investment | Arkansas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	0.00%
Residential bridge loans held-for-investment | Maryland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	0.00%
Residential bridge loans held-for-investment | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	3.00%
Residential bridge loans held-for-investment | Other states (none greater than 5%)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	34.00%	9.00%
Redwood | Single-family rental loans held-for-investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	100.00%	0.00%
Redwood | Single-family rental loans held-for-investment | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	0.00%	0.00%
Redwood | Single-family rental loans held-for-investment | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	12.00%	0.00%
Redwood | Single-family rental loans held-for-investment | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	5.00%
Redwood | Single-family rental loans held-for-investment | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	1.00%
Redwood | Single-family rental loans held-for-investment | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	1.00%	0.00%
Redwood | Single-family rental loans held-for-investment | Utah
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	0.00%	0.00%
Redwood | Single-family rental loans held-for-investment | Georgia
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	0.00%
Redwood | Single-family rental loans held-for-investment | Alabama
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	0.00%
Redwood | Single-family rental loans held-for-investment | Arkansas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	0.00%
Redwood | Single-family rental loans held-for-investment | Maryland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	0.00%
Redwood | Single-family rental loans held-for-investment | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	0.00%
Redwood | Single-family rental loans held-for-investment | Other states (none greater than 5%)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	81.00%	0.00%
CAFL | Single-family rental loans held-for-investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	100.00%	0.00%
CAFL | Single-family rental loans held-for-investment | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	8.00%	0.00%
CAFL | Single-family rental loans held-for-investment | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	15.00%	0.00%
CAFL | Single-family rental loans held-for-investment | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	11.00%
CAFL | Single-family rental loans held-for-investment | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	1.00%
CAFL | Single-family rental loans held-for-investment | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	7.00%	0.00%
CAFL | Single-family rental loans held-for-investment | Utah
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	0.00%	0.00%
CAFL | Single-family rental loans held-for-investment | Georgia
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	5.00%
CAFL | Single-family rental loans held-for-investment | Alabama
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	4.00%
CAFL | Single-family rental loans held-for-investment | Arkansas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	2.00%
CAFL | Single-family rental loans held-for-investment | Maryland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	2.00%
CAFL | Single-family rental loans held-for-investment | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	5.00%
CAFL | Single-family rental loans held-for-investment | Other states (none greater than 5%)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	40.00%	0.00%

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