Changes of Unamortized Discount and Designated Credit Reserves on Residential Available for Sale Securities (Detail) (Residential, USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2013
Residential
Credit Reserve
Beginning balance	$ 190,690	$ 187,032
Amortization of net discount
Realized credit losses	(4,117)	(11,965)
Acquisitions	3,495	8,397
Sales, calls, other	(338)	(338)
Impairments	1,642	1,666
Transfers to (release of) credit reserves	(962)	5,618
Ending Balance	190,410	190,410
Unamortized Discount Net
Beginning balance	220,568	203,421
Amortization of net discount	(8,153)	(15,847)
Realized credit losses
Acquisitions	23,102	54,523
Sales, calls, other	(633)	(633)
Impairments
Transfers to (release of) credit reserves	962	(5,618)
Ending Balance	$ 235,846	$ 235,846