Securities - Amortized Costs, Gross Unrealized Gains, Gross Unrealized Losses and Approximate Fair Values of Investment Securities (Detail) (USD $) In Thousands, unless otherwise specified														9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Aug. 31, 2012	Sep. 30, 2013 U.S. Government & Agencies [Member]	Dec. 31, 2012 U.S. Government & Agencies [Member]	Sep. 30, 2013 Obligations of State and Political Subdivisions [Member]	Dec. 31, 2012 Obligations of State and Political Subdivisions [Member]	Sep. 30, 2013 Residential Mortgage Backed Securities and Collateralized Mortgage Obligations [Member]	Dec. 31, 2012 Residential Mortgage Backed Securities and Collateralized Mortgage Obligations [Member]	Sep. 30, 2013 Corporate Securities [Member]	Dec. 31, 2012 Corporate Securities [Member]	Sep. 30, 2013 Other Asset Backed Securities [Member]	Dec. 31, 2012 Other Asset Backed Securities [Member]	Sep. 30, 2013 Obligations of States and Political Subdivisions [Member]	Dec. 31, 2012 Obligations of States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity securities, Amortized Costs	$ 34,814	$ 31,483												$ 34,814	$ 31,483
Held-to-maturity securities, Gross Unrealized Gains														32	60
Held-to-maturity securities, Gross Unrealized Losses														(2,944)	(50)
Held-to-maturity securities, Estimated Fair Value	31,902													31,902	31,493
Available-for-sale securities, Amortized Costs	213,896	194,423		4,024	2,970	63,118	56,802	59,013	51,177	53,279	60,516	34,462	22,958
Available-for-sale securities, Gross Unrealized Gains	1,852	4,096	874	0	0	658	1,797	374	670	379	1,358	441	271
Available-for-sale securities, Gross Unrealized Losses	(6,106)	(1,165)	(35)	(306)	(24)	(2,284)	(115)	(1,453)	(317)	(1,106)	(318)	(957)	(391)
Available-for-sale securities, Estimated Fair Value	$ 209,642	$ 197,354	$ 18,800	$ 3,718	$ 2,946	$ 61,492	$ 58,484	$ 57,934	$ 51,530	$ 52,552	$ 61,556	$ 33,946	$ 22,838