Fair Values of Real Estate Securities by Collateral Type and Entity (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Investment Holdings [Line Items]
Real Estate Securities	$ 1,312,347	$ 981,837
Residential
Investment Holdings [Line Items]
Real Estate Securities	1,245,616	919,343
Commercial
Investment Holdings [Line Items]
Real Estate Securities	51,062	43,368
CDO
Investment Holdings [Line Items]
Real Estate Securities	15,669	19,126
Redwood
Investment Holdings [Line Items]
Real Estate Securities	1,069,275	750,736
Redwood | Residential
Investment Holdings [Line Items]
Real Estate Securities	1,061,592	744,281
Redwood | Commercial
Investment Holdings [Line Items]
Real Estate Securities	7,619	5,445
Redwood | CDO
Investment Holdings [Line Items]
Real Estate Securities	64	1,010
Acacia
Investment Holdings [Line Items]
Real Estate Securities	243,072	231,101
Acacia | Residential
Investment Holdings [Line Items]
Real Estate Securities	184,024	175,062
Acacia | Commercial
Investment Holdings [Line Items]
Real Estate Securities	43,443	37,923
Acacia | CDO
Investment Holdings [Line Items]
Real Estate Securities	$ 15,605	$ 18,116