Securities - Amortized Cost and Fair Value of Securities with Gross Unrealized Gains and Losses (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 243,776	$ 247,819
Gross Unrealized Gains	2,851	2,619
Gross Unrealized Losses	(557)	(1,946)
Estimated Market Value	246,070	248,492
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	33,989	25,833
Gross Unrealized Gains	11
Gross Unrealized Losses	(129)	(440)
Estimated Market Value	33,871	25,393
U.S. Government Agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	106,374	120,154
Gross Unrealized Gains	410	391
Gross Unrealized Losses	(309)	(1,311)
Estimated Market Value	106,475	119,234
Mortgage-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	27,435	29,067
Gross Unrealized Gains	621	557
Gross Unrealized Losses	(40)	(62)
Estimated Market Value	28,016	29,562
State and Local Governments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	75,978	72,765
Gross Unrealized Gains	1,809	1,671
Gross Unrealized Losses	(79)	(133)
Estimated Market Value	$ 77,708	$ 74,303

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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Amount of debt securities categorized neither as held-to-maturity nor trading.

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