Principles of Consolidation - Summary of Unconsolidated Variable Interest Entity's Sponsored by Redwood (Details) - Variable Interest Entity, Not Primary Beneficiary - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
On-balance sheet assets, at fair value:
Maximum loss exposure	$ 286,163	$ 349,997
Assets transferred:
Principal balance of loans outstanding	10,360,700	10,580,216
Principal balance of loans 30 days delinquent	28,782	21,805
Interest-only, senior and subordinate securities, classified as trading
On-balance sheet assets, at fair value:
Securities	106,691	129,111
Subordinate securities, classified as AFS
On-balance sheet assets, at fair value:
Securities	141,568	162,314
Mortgage servicing rights
On-balance sheet assets, at fair value:
Securities	$ 37,904	$ 58,572