Securities - Gross Unrealized Losses and Fair Value of Company's Investments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	$ 190,663	$ 41,837
Fair value more than 12 months	5,532
Total fair value	196,195	41,837
Unrealized losses less than 12 months	(6,571)	(168)
Unrealized losses more than 12 months	(145)
Total unrealized losses	(6,716)	(168)
U.S.Treasury and Federal Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	27,836	13,064
Fair value more than 12 months
Total fair value	27,836	13,064
Unrealized losses less than 12 months	(647)	(30)
Unrealized losses more than 12 months
Total unrealized losses	(647)	(30)
State and Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	53,822	11,928
Fair value more than 12 months	1,033
Total fair value	54,855	11,928
Unrealized losses less than 12 months	(2,686)	(84)
Unrealized losses more than 12 months	(13)
Total unrealized losses	(2,699)	(84)
Federal Agency Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	56,488	12,719
Fair value more than 12 months	4,499
Total fair value	60,987	12,719
Unrealized losses less than 12 months	(1,645)	(39)
Unrealized losses more than 12 months	(132)
Total unrealized losses	(1,777)	(39)
Federal Agency Mortgage-Backed Pools [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value less than 12 months	52,517	4,126
Fair value more than 12 months
Total fair value	52,517	4,126
Unrealized losses less than 12 months	(1,593)	(15)
Unrealized losses more than 12 months
Total unrealized losses	$ (1,593)	$ (15)