Recorded Investment in Residential Loans Held-For-Investment Organized by Year of Origination (Detail) (Residential Loans Held for Investment, USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Residential loans	$ 1,887,868	$ 2,301,316
2003 & Earlier
Financing Receivable, Recorded Investment [Line Items]
Residential loans	942,405	1,131,200
2004
Financing Receivable, Recorded Investment [Line Items]
Residential loans	528,728	569,379
2005
Financing Receivable, Recorded Investment [Line Items]
Residential loans	66,821	71,792
2006
Financing Receivable, Recorded Investment [Line Items]
Residential loans	151,067	164,333
2009
Financing Receivable, Recorded Investment [Line Items]
Residential loans	30,395	58,628
2010
Financing Receivable, Recorded Investment [Line Items]
Residential loans	102,385	197,964
2011
Financing Receivable, Recorded Investment [Line Items]
Residential loans	$ 66,067	$ 108,020