Principles of Consolidation - Key Assumptions and Sensitivity Analysis for Assets Retained from Unconsolidated Variable Interest Entity's Sponsored by Redwood (Details) - Variable Interest Entity, Not Primary Beneficiary - USD ($) $ in Thousands			3 Months Ended	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Mar. 31, 2020	Sep. 30, 2020
MSRs
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Fair value	$ 14,240	$ 40,254		$ 14,240
Expected life (in years)	3 years	6 years
Prepayment speed assumption (annual CPR)	26.00%	11.00%
Decrease in fair value from:
10% adverse change	$ 1,105	$ 1,643		1,105
25% adverse change	$ 2,678	$ 3,913		2,678
Discount rate assumption	12.00%	11.00%
Decrease in fair value from:
100 basis point increase	$ 383	$ 1,447		383
200 basis point increase	746	2,795		746
Senior Securities
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Fair value	$ 16,226	$ 48,765		16,226
Expected life (in years)	3 years	6 years
Prepayment speed assumption (annual CPR)	30.00%	14.00%
Decrease in fair value from:
10% adverse change	$ 1,622	$ 1,908		1,622
25% adverse change	$ 3,675	$ 5,086		3,675
Discount rate assumption	17.00%	12.00%
Decrease in fair value from:
100 basis point increase	$ 327	$ 1,079		327
200 basis point increase	$ 638	$ 2,482		638
Credit loss assumption	0.38%	0.21%
Decrease in fair value from:
10% higher losses	$ 0	$ 0		0
25% higher losses	0	0		0
Subordinate Securities
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Fair value	$ 127,783	$ 180,309		127,783
Expected life (in years)	10 years	14 years
Prepayment speed assumption (annual CPR)	27.00%	16.00%
Decrease in fair value from:
10% adverse change	$ 1,075	$ 205		1,075
25% adverse change	$ 3,735	$ 1,434		3,735
Discount rate assumption	6.00%	5.00%
Decrease in fair value from:
100 basis point increase	$ 10,219	$ 18,127		10,219
200 basis point increase	$ 19,348	$ 33,630		19,348
Credit loss assumption	0.38%	0.21%
Decrease in fair value from:
10% higher losses	$ 2,274	$ 1,804		2,274
25% higher losses	$ 5,500	$ 4,520		$ 5,500
Minimum | MSRs
Decrease in fair value from:
Impact of adverse change in prepayment speed			10.00%	10.00%
Impact of increase in discount rate assumption			1.00%	1.00%
Impact of adverse change in expected credit losses			10.00%	10.00%
Minimum | Senior Securities
Decrease in fair value from:
Impact of adverse change in prepayment speed			10.00%	10.00%
Impact of increase in discount rate assumption			1.00%	1.00%
Impact of adverse change in expected credit losses			10.00%	10.00%
Minimum | Subordinate Securities
Decrease in fair value from:
Impact of adverse change in prepayment speed			10.00%	10.00%
Impact of increase in discount rate assumption			1.00%	1.00%
Impact of adverse change in expected credit losses			10.00%	10.00%
Maximum | MSRs
Decrease in fair value from:
Impact of adverse change in prepayment speed			25.00%	25.00%
Impact of increase in discount rate assumption			2.00%	2.00%
Impact of adverse change in expected credit losses			25.00%	25.00%
Maximum | Senior Securities
Decrease in fair value from:
Impact of adverse change in prepayment speed			25.00%	25.00%
Impact of increase in discount rate assumption			2.00%	2.00%
Impact of adverse change in expected credit losses			25.00%	25.00%
Maximum | Subordinate Securities
Decrease in fair value from:
Impact of adverse change in prepayment speed			25.00%	25.00%
Impact of increase in discount rate assumption			2.00%	2.00%
Impact of adverse change in expected credit losses			25.00%	25.00%