Business Purpose Loans - Product Types and Characteristics of Business Purpose Loans (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) loan	Dec. 31, 2019 USD ($) loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	198	669
Total Principal	$ 172,748	$ 524,928
30-89 Days DQ	3,362	1,650
90+ Days DQ	$ 1,882	$ 747
Single-family rental loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	65	201
Total Principal	$ 234,475	$ 321,637
30-89 Days DQ	0	0
90+ Days DQ	7,127	$ 1,818
Single-family rental loans | $0 to $250
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balance, minimum	0
Loan Balance, maximum	$ 250
Number of Loans | loan	8	85
Total Principal	$ 1,060	$ 10,506
30-89 Days DQ	0	0
90+ Days DQ	$ 635	$ 130
Single-family rental loans | $0 to $250 | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	6.25%	5.50%
Single-family rental loans | $0 to $250 | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	7.75%	7.63%
Single-family rental loans | $251 to $500
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balance, minimum	$ 251	$ 251
Loan Balance, maximum	$ 500	$ 500
Number of Loans | loan	1	9
Total Principal	$ 483	$ 3,708
30-89 Days DQ	0	0
90+ Days DQ	$ 0	$ 0
Single-family rental loans | $251 to $500 | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	5.97%	4.94%
Single-family rental loans | $251 to $500 | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	5.97%	6.00%
Single-family rental loans | $501 to $750
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balance, minimum	$ 501	$ 501
Loan Balance, maximum	$ 750	$ 750
Number of Loans | loan	6	21
Total Principal	$ 3,632	$ 13,335
30-89 Days DQ	0	0
90+ Days DQ	$ 0	$ 0
Single-family rental loans | $501 to $750 | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	5.84%	4.55%
Single-family rental loans | $501 to $750 | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	6.75%	5.96%
Single-family rental loans | $751 to $1,000
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balance, minimum	$ 751	$ 751
Loan Balance, maximum	$ 1,000	$ 1,000
Number of Loans | loan	10	13
Total Principal	$ 8,936	$ 11,676
30-89 Days DQ	0	0
90+ Days DQ	$ 1,815	$ 0
Single-family rental loans | $751 to $1,000 | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	5.15%	5.00%
Single-family rental loans | $751 to $1,000 | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	6.39%	5.93%
Single-family rental loans | Over $1,000
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balance, maximum	$ 1,000	$ 1,000
Number of Loans | loan	40	73
Total Principal	$ 220,364	$ 282,412
30-89 Days DQ	0	0
90+ Days DQ	$ 4,677	$ 1,688
Single-family rental loans | Over $1,000 | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	3.82%	4.35%
Single-family rental loans | Over $1,000 | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	5.95%	6.28%
Bridge loans held-for-investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	1,725	2,653
Total Principal	$ 649,532	$ 741,232
30-89 Days DQ	7,475	39,553
90+ Days DQ	39,415	8,987
Bridge loans held-for-investment | $0 to $250
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balance, minimum	0	0
Loan Balance, maximum	$ 250	$ 250
Number of Loans | loan	1,440	2,207
Total Principal	$ 128,596	$ 197,449
30-89 Days DQ	6,530	1,447
90+ Days DQ	$ 1,668	$ 369
Bridge loans held-for-investment | $0 to $250 | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	5.75%	6.53%
Bridge loans held-for-investment | $0 to $250 | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	12.00%	12.00%
Bridge loans held-for-investment | $251 to $500
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balance, minimum	$ 251	$ 251
Loan Balance, maximum	$ 500	$ 500
Number of Loans | loan	110	198
Total Principal	$ 37,607	$ 71,361
30-89 Days DQ	945	2,811
90+ Days DQ	$ 1,423	$ 675
Bridge loans held-for-investment | $251 to $500 | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	6.65%	6.99%
Bridge loans held-for-investment | $251 to $500 | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	13.00%	13.00%
Bridge loans held-for-investment | $501 to $750
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balance, minimum	$ 501	$ 501
Loan Balance, maximum	$ 750	$ 750
Number of Loans | loan	39	71
Total Principal	$ 23,783	$ 42,862
30-89 Days DQ	0	2,072
90+ Days DQ	$ 540	$ 508
Bridge loans held-for-investment | $501 to $750 | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	6.99%	6.99%
Bridge loans held-for-investment | $501 to $750 | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	10.00%	9.99%
Bridge loans held-for-investment | $751 to $1,000
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balance, minimum	$ 751	$ 751
Loan Balance, maximum	$ 1,000	$ 1,000
Number of Loans | loan	21	40
Total Principal	$ 18,225	$ 34,646
30-89 Days DQ	0	1,771
90+ Days DQ	$ 943	$ 2,443
Bridge loans held-for-investment | $751 to $1,000 | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	6.50%	7.28%
Bridge loans held-for-investment | $751 to $1,000 | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	9.50%	10.00%
Bridge loans held-for-investment | Over $1,000
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balance, maximum	$ 1,000	$ 1,000
Number of Loans | loan	115	137
Total Principal	$ 441,321	$ 394,914
30-89 Days DQ	0	31,452
90+ Days DQ	$ 34,841	$ 4,992
Bridge loans held-for-investment | Over $1,000 | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	6.04%	5.79%
Bridge loans held-for-investment | Over $1,000 | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	10.25%	10.25%
Redwood | Single-family rental loans held-for-investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan		107
Total Principal		$ 231,211
30-89 Days DQ		0
90+ Days DQ		$ 0
Redwood | Single-family rental loans held-for-investment | $251 to $500
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan		20
Total Principal		$ 7,925
30-89 Days DQ		0
90+ Days DQ		$ 0
Redwood | Single-family rental loans held-for-investment | $251 to $500 | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate		4.88%
Redwood | Single-family rental loans held-for-investment | $251 to $500 | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate		7.47%
Redwood | Single-family rental loans held-for-investment | $501 to $750
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan		26
Total Principal		$ 15,620
30-89 Days DQ		0
90+ Days DQ		$ 0
Redwood | Single-family rental loans held-for-investment | $501 to $750 | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate		4.45%
Redwood | Single-family rental loans held-for-investment | $501 to $750 | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate		7.25%
Redwood | Single-family rental loans held-for-investment | $751 to $1,000
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan		16
Total Principal		$ 13,616
30-89 Days DQ		0
90+ Days DQ		$ 0
Redwood | Single-family rental loans held-for-investment | $751 to $1,000 | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate		4.91%
Redwood | Single-family rental loans held-for-investment | $751 to $1,000 | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate		6.58%
Redwood | Single-family rental loans held-for-investment | Over $1,000
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan		45
Total Principal		$ 194,050
30-89 Days DQ		0
90+ Days DQ		$ 0
Redwood | Single-family rental loans held-for-investment | Over $1,000 | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate		3.93%
Redwood | Single-family rental loans held-for-investment | Over $1,000 | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate		6.94%
CAFL | Single-family rental loans held-for-investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	1,094	783
Total Principal	$ 3,017,137	$ 2,078,214
30-89 Days DQ	4,631	22,771
90+ Days DQ	61,440	$ 29,039
CAFL | Single-family rental loans held-for-investment | $0 to $250
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balance, minimum	0
Loan Balance, maximum	$ 250
Number of Loans | loan	5	2
Total Principal	$ 1,016	$ 398
30-89 Days DQ	0	0
90+ Days DQ	$ 0	$ 0
CAFL | Single-family rental loans held-for-investment | $0 to $250 | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	5.77%	5.46%
CAFL | Single-family rental loans held-for-investment | $0 to $250 | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	7.05%	5.80%
CAFL | Single-family rental loans held-for-investment | $251 to $500
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balance, minimum	$ 251
Loan Balance, maximum	$ 500
Number of Loans | loan	67	56
Total Principal	$ 29,977	$ 25,643
30-89 Days DQ	0	1,306
90+ Days DQ	$ 0	$ 0
CAFL | Single-family rental loans held-for-investment | $251 to $500 | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	4.64%	4.92%
CAFL | Single-family rental loans held-for-investment | $251 to $500 | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	6.96%	7.05%
CAFL | Single-family rental loans held-for-investment | $501 to $750
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balance, minimum	$ 501
Loan Balance, maximum	$ 750
Number of Loans | loan	212	148
Total Principal	$ 130,665	$ 91,414
30-89 Days DQ	0	1,259
90+ Days DQ	$ 1,752	$ 1,990
CAFL | Single-family rental loans held-for-investment | $501 to $750 | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	4.12%	4.75%
CAFL | Single-family rental loans held-for-investment | $501 to $750 | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	7.06%	7.31%
CAFL | Single-family rental loans held-for-investment | $751 to $1,000
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balance, minimum	$ 751
Loan Balance, maximum	$ 1,000
Number of Loans | loan	131	98
Total Principal	$ 113,874	$ 85,472
30-89 Days DQ	764	1,639
90+ Days DQ	$ 750	$ 879
CAFL | Single-family rental loans held-for-investment | $751 to $1,000 | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	4.33%	4.62%
CAFL | Single-family rental loans held-for-investment | $751 to $1,000 | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	7.23%	7.23%
CAFL | Single-family rental loans held-for-investment | Over $1,000
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Balance, maximum	$ 1,000
Number of Loans | loan	679	479
Total Principal	$ 2,741,605	$ 1,875,287
30-89 Days DQ	3,867	18,567
90+ Days DQ	$ 58,938	$ 26,170
CAFL | Single-family rental loans held-for-investment | Over $1,000 | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	3.93%	4.31%
CAFL | Single-family rental loans held-for-investment | Over $1,000 | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Rate	7.57%	7.57%