Components of Carrying Value (Which Equals Fair Value) of Residential Available for Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	$ 1,172,690		$ 1,075,581
Residential
Schedule of Available-for-sale Securities [Line Items]
Principal balance	1,453,596		1,277,401
Credit reserve	(190,410)	(190,690)	(187,032)
Unamortized discount, net	(235,846)	(220,568)	(203,421)
Amortized cost	1,027,340		886,948
Gross unrealized gains	158,883		176,929
Gross unrealized losses	(13,533)		(2,365)
Carrying Value	$ 1,172,690		$ 1,061,512