Investment Securities (Narrative) (Detail) (USD $)	6 Months Ended
	Jun. 30, 2014 Securities	Dec. 31, 2013	Jun. 30, 2013
Investment [Line Items]
Amount of securities pledged to secure public funds and other purposes as required by law	$ 1,340,493,000	$ 1,512,824,000
Number of non-agency residential mortgage-backed securities that had unrealized losses	1
Number of non-agency residential mortgage-backed securities rated below investment grade	0
Number of non-agency residential mortgage-backed securities that have subprime or Alt-A components	0
Number of non-agency residential-mortgage backed securities with other-than-temporary impairment	0
Accumulated other comprehensive income (loss), other-than- temporarily impaired securities	0		471,000
Minimum [Member]
Investment [Line Items]
Number of days mortgage is past due related to cumulative default rate	60 days
Maximum [Member]
Investment [Line Items]
Number of days mortgage is past due related to cumulative default rate	90 days
Other Structured Financial Products [Member]
Investment [Line Items]
Unrealized loss	$ 12,746,000		$ 14,543,000