Principles of Consolidation - Summary of Unconsolidated Variable Interest Entity's Sponsored by Redwood (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
On-balance sheet assets, at fair value:
Available-for-sale securities	$ 207,173	$ 239,334
Servicing asset, fair value	242,059	151,582
Mortgage servicing rights
On-balance sheet assets, at fair value:
Servicing asset, fair value	14,878	42,224
Variable Interest Entity, Not Primary Beneficiary
On-balance sheet assets, at fair value:
Maximum loss exposure	158,250	269,328
Assets transferred:
Principal balance of loans outstanding	8,571,916	10,299,442
Principal balance of loans 30+ days delinquent	200,910	41,809
Variable Interest Entity, Not Primary Beneficiary | Interest-only, senior and subordinate securities, classified as trading
On-balance sheet assets, at fair value:
Interest-only, senior and subordinate securities, classified as trading	19,878	88,425
Variable Interest Entity, Not Primary Beneficiary | Subordinate securities, classified as AFS
On-balance sheet assets, at fair value:
Available-for-sale securities	124,132	140,649
Variable Interest Entity, Not Primary Beneficiary | Mortgage servicing rights
On-balance sheet assets, at fair value:
Servicing asset, fair value	$ 14,240	$ 40,254