Securities - Fair Value of Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	$ 455,502	$ 444,062
Gross Unrealized Gains	7,427	3,971
Held-to-maturity, Amortized Cost	180,291	187,629
Gross Unrealized Losses	(453)	(3,051)
Held-to-maturity, Gross Unrealized Gains	8,038	6,636
Available-for-sale Securities, Fair Value	462,476	444,982
Held-to-maturity, Gross Unrealized Losses	(236)	(562)
Held-to-maturity, Fair Value	188,093	193,703
U.S. Treasury and Federal Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	15,412	5,940
Gross Unrealized Gains	60	3
Held-to-maturity, Amortized Cost		5,859
Gross Unrealized Losses	(2)	(17)
Held-to-maturity, Gross Unrealized Gains		93
Available-for-sale Securities, Fair Value	15,470	5,926
Held-to-maturity, Fair Value		5,952
State and Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	69,204	73,829
Gross Unrealized Gains	1,840	1,299
Held-to-maturity, Amortized Cost	145,520	146,331
Gross Unrealized Losses	(2)	(33)
Held-to-maturity, Gross Unrealized Gains	6,753	5,375
Available-for-sale Securities, Fair Value	71,042	75,095
Held-to-maturity, Gross Unrealized Losses	(188)	(253)
Held-to-maturity, Fair Value	152,085	151,453
Federal Agency Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	155,687	157,291
Gross Unrealized Gains	1,836	567
Held-to-maturity, Amortized Cost	8,731	9,051
Gross Unrealized Losses	(210)	(1,655)
Held-to-maturity, Gross Unrealized Gains	136	27
Available-for-sale Securities, Fair Value	157,313	156,203
Held-to-maturity, Gross Unrealized Losses		(124)
Held-to-maturity, Fair Value	8,867	8,954
Federal Agency Mortgage-backed Pools [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	215,167	206,970
Gross Unrealized Gains	3,648	2,080
Held-to-maturity, Amortized Cost	26,040	26,388
Gross Unrealized Losses	(239)	(1,346)
Held-to-maturity, Gross Unrealized Gains	1,149	1,141
Available-for-sale Securities, Fair Value	218,576	207,704
Held-to-maturity, Gross Unrealized Losses	(48)	(185)
Held-to-maturity, Fair Value	27,141	27,344
Corporate Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	32	32
Gross Unrealized Gains	43	22
Available-for-sale Securities, Fair Value	$ 75	$ 54

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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