Principles of Consolidation - Summary of Unconsolidated Variable Interest Entity's Sponsored by Redwood (Detail) - Variable Interest Entity, Not Primary Beneficiary - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
On-balance sheet assets, at fair value:
Maximum loss exposure	$ 407,490	$ 611,593
Principal balance of loans outstanding	7,289,025	7,276,825
Principal balance of delinquent loans 30+ days delinquent	14,204	17,022
Interest-only, senior and subordinate securities, classified as trading
On-balance sheet assets, at fair value:
Securities	61,602	93,802
Senior and subordinate securities, classified as AFS
On-balance sheet assets, at fair value:
Securities	292,948	460,990
Mortgage servicing rights
On-balance sheet assets, at fair value:
Securities	$ 52,940	$ 56,801