Securities - Cash Proceeds from Sales Securities and Gross Realized Gains and Gross Realized Losses Included Earnings (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Available-for-Sale Securities, Gross Unrealized Gain (Loss) [Line Items]
Proceeds from sales of securities	$ 32,502	$ 18,450	$ 77,845	$ 72,261
Gross realized gains on sales of securities:
Total gross realized gains on sales of securities	589	579	931	1,737
Gross realized losses on sales of securities
Total gross realized losses on sales of securities	(253)	(29)	(353)	(129)
Gain on investment securities, net	336	550	931	1,737
Obligations of States and Political Subdivisions [Member]
Gross realized gains on sales of securities:
Total gross realized gains on sales of securities	35	399	212	1,276
Gross realized losses on sales of securities
Total gross realized losses on sales of securities	(108)	0	(118)	0
Residential Mortgage Backed Securities and Collateralized Mortgage Obligations [Member]
Gross realized gains on sales of securities:
Total gross realized gains on sales of securities	135	77	240	260
Gross realized losses on sales of securities
Total gross realized losses on sales of securities	(13)	(29)	(63)	(110)
Corporate Securities [Member]
Gross realized gains on sales of securities:
Total gross realized gains on sales of securities	419	101	780	316
Gross realized losses on sales of securities
Total gross realized losses on sales of securities	(12)	0	(25)	(16)
Other Asset Backed Securities [Member]
Gross realized gains on sales of securities:
Total gross realized gains on sales of securities	0	2	52	14
Gross realized losses on sales of securities
Total gross realized losses on sales of securities	(47)	0	(47)	(3)
U.S. Government and Agencies [Member]
Gross realized losses on sales of securities
Total gross realized losses on sales of securities	$ (73)	$ 0	$ (100)	$ 0