Fair Value - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Available-for-sale securities
Total assets measured at fair value	$ 209,642	$ 197,354
Total liabilities measured at fair value	2,844	4,085
U.S. Government and Agencies [Member]
Available-for-sale securities
Total assets measured at fair value	3,718	2,946
Obligations of States and Political Subdivisions [Member]
Available-for-sale securities
Total assets measured at fair value	61,492	58,484
Corporate Securities [Member]
Available-for-sale securities
Total assets measured at fair value	52,552	61,556
Other investment securities [Member]
Available-for-sale securities
Total assets measured at fair value	91,880	74,368
Interest Rate Swap Contracts [Member]
Available-for-sale securities
Total liabilities measured at fair value	2,844	4,085
Level 1 [Member]
Available-for-sale securities
Total assets measured at fair value	0	0
Total liabilities measured at fair value	0	0
Level 1 [Member] | U.S. Government and Agencies [Member]
Available-for-sale securities
Total assets measured at fair value	0	0
Level 1 [Member] | Obligations of States and Political Subdivisions [Member]
Available-for-sale securities
Total assets measured at fair value	0
Level 1 [Member] | Corporate Securities [Member]
Available-for-sale securities
Total assets measured at fair value	0	0
Level 1 [Member] | Other investment securities [Member]
Available-for-sale securities
Total assets measured at fair value	0	0
Level 1 [Member] | Interest Rate Swap Contracts [Member]
Available-for-sale securities
Total liabilities measured at fair value	0	0
Level 2 [Member]
Available-for-sale securities
Total assets measured at fair value	209,642	182,476
Total liabilities measured at fair value	2,844	4,085
Level 2 [Member] | U.S. Government and Agencies [Member]
Available-for-sale securities
Total assets measured at fair value	3,718	2,946
Level 2 [Member] | Obligations of States and Political Subdivisions [Member]
Available-for-sale securities
Total assets measured at fair value	61,492	57,353
Level 2 [Member] | Corporate Securities [Member]
Available-for-sale securities
Total assets measured at fair value	52,552	61,556
Level 2 [Member] | Other investment securities [Member]
Available-for-sale securities
Total assets measured at fair value	91,880	60,621
Level 2 [Member] | Interest Rate Swap Contracts [Member]
Available-for-sale securities
Total liabilities measured at fair value	2,844	4,085
Level 3 [Member]
Available-for-sale securities
Total assets measured at fair value	0	14,878
Total liabilities measured at fair value	0	0
Level 3 [Member] | U.S. Government and Agencies [Member]
Available-for-sale securities
Total assets measured at fair value	0	0
Level 3 [Member] | Obligations of States and Political Subdivisions [Member]
Available-for-sale securities
Total assets measured at fair value	0	1,131
Level 3 [Member] | Corporate Securities [Member]
Available-for-sale securities
Total assets measured at fair value	0	0
Level 3 [Member] | Other investment securities [Member]
Available-for-sale securities
Total assets measured at fair value	0	13,747
Level 3 [Member] | Interest Rate Swap Contracts [Member]
Available-for-sale securities
Total liabilities measured at fair value	$ 0	$ 0