Securities - Fair Value of Securities (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	$ 325,176	$ 319,746
Held-to-maturity, Amortized Cost	164,282us-gaap_HeldToMaturitySecurities	165,767us-gaap_HeldToMaturitySecurities
Gross Unrealized Gains	6,725	5,697
Held-to-maturity, Gross Unrealized Gains	7,342	4,244
Gross Unrealized Losses	(868)	(1,679)
Held-to-maturity, Gross Unrealized Losses	(219)	(107)
Available-for-sale Securities, Fair Value	331,033us-gaap_AvailableForSaleSecurities	323,764us-gaap_AvailableForSaleSecurities
Held-to-maturity, Fair Value	171,405	169,904
U.S. Treasury and Federal Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	28,400	26,996
Held-to-maturity, Amortized Cost	9,824	9,804
Gross Unrealized Gains	69	56
Held-to-maturity, Gross Unrealized Gains	157	82
Gross Unrealized Losses	(48)	(229)
Available-for-sale Securities, Fair Value	28,421	26,823
Held-to-maturity, Fair Value	9,981	9,886
State and Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	50,036	46,535
Held-to-maturity, Amortized Cost	128,558	129,595
Gross Unrealized Gains	1,577	1,462
Held-to-maturity, Gross Unrealized Gains	6,179	3,398
Gross Unrealized Losses	(37)	(45)
Held-to-maturity, Gross Unrealized Losses	(143)	(106)
Available-for-sale Securities, Fair Value	51,576	47,952
Held-to-maturity, Fair Value	134,594	132,887
Federal Agency Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	120,785	122,930
Held-to-maturity, Amortized Cost	3,873	4,039
Gross Unrealized Gains	1,471	975
Held-to-maturity, Gross Unrealized Gains	45	35
Gross Unrealized Losses	(537)	(1,045)
Held-to-maturity, Gross Unrealized Losses		(1)
Available-for-sale Securities, Fair Value	121,719	122,860
Held-to-maturity, Fair Value	3,918	4,073
Federal Agency Mortgage-backed Pools [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	125,923	122,583
Held-to-maturity, Amortized Cost	22,027	22,329
Gross Unrealized Gains	3,590	3,172
Held-to-maturity, Gross Unrealized Gains	961	729
Gross Unrealized Losses	(246)	(360)
Held-to-maturity, Gross Unrealized Losses	(76)
Available-for-sale Securities, Fair Value	129,267	125,395
Held-to-maturity, Fair Value	22,912	23,058
Private Labeled Mortgage-backed Pools [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost		670
Gross Unrealized Gains		19
Available-for-sale Securities, Fair Value		689
Corporate Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale investment securities, Amortized Cost	32	32
Gross Unrealized Gains	18	13
Available-for-sale Securities, Fair Value	$ 50	$ 45

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

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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