Investment Securities (Credit Losses on Non-Agency Residential Mortgage-Backed Securities) (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Disclosure Investment Securities Credit Losses On Non Agency Residential Mortgage Backed Securities [Abstract]
Balance	$ 1,635,000	$ 1,566,000	$ 1,280,000	$ 4,602,000
Amount related to credit losses for which an other-than-temporary impairment was not previously recognized	0	0	325,000	0
Additional amount related to credit losses for which an other-than-temporary impairment was previously recognized	0	0	160,000	144,000
Realized losses	26,000	0	156,000	0
Sale of securities for which other-than-temporary impairment was previously recognized	0	0	0	3,180,000
Balance	$ 1,609,000	$ 1,566,000	$ 1,609,000	$ 1,566,000