Securities - Current Fair Value and Associated Unrealized Losses on Investments with Unrealized Losses (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Investment Securities Held To Maturity [Line Items]
Less than 12 months, Fair Value	$ 127,254	$ 51,419
Less than 12 months, Unrealized Losses	(5,778)	(748)
12 months or more, Fair Value	6,803	10,009
12 months or more, Unrealized Losses	(328)	(417)
Total, Fair Value	134,057	61,428
Total, Unrealized Losses	(6,106)	(1,165)
Obligations of States and Political Subdivisions [Member]
Investment Securities Held To Maturity [Line Items]
Less than 12 months, Fair Value	37,918	8,443
Less than 12 months, Unrealized Losses	(2,258)	(109)
12 months or more, Fair Value	982	166
12 months or more, Unrealized Losses	(26)	(6)
Total, Fair Value	38,900	8,609
Total, Unrealized Losses	(2,284)	(115)
Less than 12 months, Fair Value	30,128	11,154
Less than 12 months, Unrealized Losses	(2,906)	(50)
12 months or more, Fair Value	408	0
12 months or more, Unrealized Losses	(38)	0
Total, Fair Value	30,536	11,154
Total, Unrealized Losses	(2,944)	(50)
U.S. Government and Agencies [Member]
Investment Securities Held To Maturity [Line Items]
Less than 12 months, Fair Value	3,718	2,947
Less than 12 months, Unrealized Losses	(306)	(24)
12 months or more, Fair Value	0	0
12 months or more, Unrealized Losses	0	0
Total, Fair Value	3,718	2,947
Total, Unrealized Losses	(306)	(24)
Residential Mortgage Backed Securities and Collateralized Mortgage Obligations [Member]
Investment Securities Held To Maturity [Line Items]
Less than 12 months, Fair Value	35,375	14,367
Less than 12 months, Unrealized Losses	(1,410)	(288)
12 months or more, Fair Value	2,468	1,662
12 months or more, Unrealized Losses	(43)	(29)
Total, Fair Value	37,843	16,029
Total, Unrealized Losses	(1,453)	(317)
Corporate Securities [Member]
Investment Securities Held To Maturity [Line Items]
Less than 12 months, Fair Value	32,972	16,036
Less than 12 months, Unrealized Losses	(1,021)	(85)
12 months or more, Fair Value	1,911	6,762
12 months or more, Unrealized Losses	(85)	(233)
Total, Fair Value	34,883	22,798
Total, Unrealized Losses	(1,106)	(318)
Other Asset Backed Securities [Member]
Investment Securities Held To Maturity [Line Items]
Less than 12 months, Fair Value	17,271	9,626
Less than 12 months, Unrealized Losses	(783)	(242)
12 months or more, Fair Value	1,442	1,419
12 months or more, Unrealized Losses	(174)	(149)
Total, Fair Value	18,713	11,045
Total, Unrealized Losses	$ (957)	$ (391)