Investment Securities (Credit Losses on Non-Agency Residential Mortgage-Backed Securities) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Balance	$ 1,634	$ 4,746	$ 1,280	$ 4,602
Amount related to credit losses for which an other-than-temporary impairment was not previously recognized	0	0	325	0
Additional amount related to credit losses for which an other-than-temporary impairment was previously recognized	97	0	160	144
Realized losses	96	0	130	0
Sale of securities for which other-than-temporary impairment was previously recognized	0	3,180	0	3,180
Balance	$ 1,635	$ 1,566	$ 1,635	$ 1,566