Securities - Fair Value of Securities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	$ 509,840	$ 463,306
Held-to-maturity, Amortized Cost	9,910
Gross Unrealized Gains	11,020	19,663
Gross Unrealized Losses	(6,716)	(168)
Available-for-sale Securities, Fair Value	514,144	482,801
Held-to-maturity, Fair Value	9,910
U.S.Treasury and Federal Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	43,161	51,458
Gross Unrealized Gains	243	351
Gross Unrealized Losses	(647)	(30)
Available-for-sale Securities, Fair Value	42,757	51,779
State and Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	176,711	162,147
Held-to-maturity, Amortized Cost	9,910
Gross Unrealized Gains	5,505	10,842
Held-to-maturity, Gross Unrealized Gains
Gross Unrealized Losses	(2,699)	(84)
Held-to-maturity, Gross Unrealized Losses
Available-for-sale Securities, Fair Value	179,517	172,905
Held-to-maturity, Fair Value	9,910
Federal Agency Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	111,266	95,337
Gross Unrealized Gains	1,293	1,533
Gross Unrealized Losses	(1,777)	(39)
Available-for-sale Securities, Fair Value	110,782	96,831
Federal Agency Mortgage-Backed Pools [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	176,880	152,372
Gross Unrealized Gains	3,907	6,847
Gross Unrealized Losses	(1,593)	(15)
Available-for-sale Securities, Fair Value	179,194	159,204
Private Labeled Mortgage-Backed Pools [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	1,290	1,960
Gross Unrealized Gains	44	71
Gross Unrealized Losses
Available-for-sale Securities, Fair Value	1,334	2,031
Corporate Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	532	32
Gross Unrealized Gains	28	19
Gross Unrealized Losses
Available-for-sale Securities, Fair Value	$ 560	$ 51