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
	Mar. 31, 2014
Residential
Credit Reserve
Beginning balance	$ 116,870
Amortization of net discount
Realized credit losses	(3,337)
Acquisitions
Sales, calls, other	(936)
Impairments	113
Transfers to (release of) credit reserves, net	(17,022)
Ending Balance	95,688
Unamortized Discount Net
Beginning balance	298,469
Amortization of net discount	(11,298)
Realized credit losses
Acquisitions	(409)
Sales, calls, other	(51)
Impairments
Transfers to (release of) credit reserves, net	17,022
Ending Balance	$ 303,733