Investment Securities - Reconciliation of Available-for-Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 420,455	$ 386,462
Gross Unrealized Gains	5,003	8,292
Gross Unrealized Losses	(6,896)	(1,044)
Fair Value	418,562	393,710
U.S. Treasury and U.S. Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	62,117	86,002
Gross Unrealized Gains		577
Gross Unrealized Losses	(1,953)	(8)
Fair Value	60,164	86,571
Mortgage-Backed Securities, Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	291,961	235,052
Gross Unrealized Gains	3,031	5,086
Gross Unrealized Losses	(3,994)	(579)
Fair Value	290,998	239,559
Obligations of States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	37,210	36,848
Gross Unrealized Gains	922	1,832
Gross Unrealized Losses	(441)	(60)
Fair Value	37,691	38,620
Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,560	13,576
Gross Unrealized Gains	59	189
Gross Unrealized Losses	(215)	(321)
Fair Value	13,404	13,444
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	15,607	14,984
Gross Unrealized Gains	991	608
Gross Unrealized Losses	(293)	(76)
Fair Value	$ 16,305	$ 15,516