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	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
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	$ 60,980	$ 58,800
Expected life (in years)	8 years	7 years
Prepayment speed assumption (annual CPR)	9.00%	11.00%
Decrease in fair value from:
10% adverse change	$ 2,022	$ 2,226
25% adverse change	$ 4,839	$ 5,284
Impact of adverse change in prepayment speed	25.00%	25.00%
Discount rate assumption	11.00%	11.00%
Decrease in fair value from:
100 basis point increase	$ 2,386	$ 2,088
200 basis point increase	$ 4,597	$ 4,032
Impact on discount rate of basis point increase	1.00%	1.00%
Decrease in fair value from:
Impact of adverse change in expected credit losses (as a percent)	25.00%	25.00%
Senior IO 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	$ 33,773	$ 26,618
Expected life (in years)	6 years	6 years
Prepayment speed assumption (annual CPR)	10.00%	8.00%
Decrease in fair value from:
10% adverse change	$ 1,371	$ 1,075
25% adverse change	$ 3,289	$ 2,569
Impact of adverse change in prepayment speed	25.00%	25.00%
Discount rate assumption	11.00%	8.00%
Decrease in fair value from:
100 basis point increase	$ 1,158	$ 1,105
200 basis point increase	$ 2,265	$ 2,128
Impact on discount rate of basis point increase	1.00%	1.00%
Credit loss assumption	0.25%	0.25%
Decrease in fair value from:
10% higher losses	$ 0	$ 19
25% higher losses	$ 0	$ 49
Impact of adverse change in expected credit losses (as a percent)	25.00%	25.00%
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	$ 286,908	$ 249,317
Expected life (in years)	13 years	12 years
Prepayment speed assumption (annual CPR)	11.00%	12.00%
Decrease in fair value from:
10% adverse change	$ 611	$ 997
25% adverse change	$ 1,506	$ 2,494
Impact of adverse change in prepayment speed	25.00%	25.00%
Discount rate assumption	5.00%	6.00%
Decrease in fair value from:
100 basis point increase	$ 25,827	$ 19,574
200 basis point increase	$ 47,885	$ 36,574
Impact on discount rate of basis point increase	1.00%	1.00%
Credit loss assumption	0.25%	0.25%
Decrease in fair value from:
10% higher losses	$ 1,551	$ 1,174
25% higher losses	$ 3,873	$ 2,933
Impact of adverse change in expected credit losses (as a percent)	25.00%	25.00%