Securities - Summary of Amortized Costs and Fair Values of Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Securities available for sale:
Amortized Cost	$ 90,594	$ 96,106
Gross Unrealized Gains	153	333
Gross Unrealized (Losses)	(1,492)	(1,637)
Fair Value	89,255	94,802
Securities held to maturity:
Amortized Cost	48,208	53,398
Gross Unrealized Gains	90	19
Gross Unrealized (Losses)	(596)	(708)
Fair Value	47,702	52,709
Total securities, Amortized cost	138,802	149,504
Total securities, Gross unrealized gains	243	352
Total securities, Gross unrealized (losses)	(2,088)	(2,345)
Total securities, Fair value	136,957	147,511
U.S. agency and mortgage-backed securities
Securities available for sale:
Amortized Cost	76,074	81,451
Gross Unrealized Gains	67	177
Gross Unrealized (Losses)	(1,337)	(1,457)
Fair Value	74,804	80,171
Securities held to maturity:
Amortized Cost	32,149	37,269
Gross Unrealized Gains	0	1
Gross Unrealized (Losses)	(551)	(483)
Fair Value	31,598	36,787
Obligations of states and political subdivisions
Securities available for sale:
Amortized Cost	14,520	14,654
Gross Unrealized Gains	86	146
Gross Unrealized (Losses)	(155)	(180)
Fair Value	14,451	14,620
Securities held to maturity:
Amortized Cost	14,559	14,629
Gross Unrealized Gains	74	18
Gross Unrealized (Losses)	(45)	(211)
Fair Value	14,588	14,436
Corporate equity securities
Securities available for sale:
Amortized Cost		1
Gross Unrealized Gains		10
Gross Unrealized (Losses)		0
Fair Value		11
Corporate debt securities
Securities held to maturity:
Amortized Cost	1,500	1,500
Gross Unrealized Gains	16	0
Gross Unrealized (Losses)	0	(14)
Fair Value	$ 1,516	$ 1,486

Available for sale and held to maturity securities accumulated gross unrealized loss.

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Available for sale securities and held to maturity securities accumulated gross unrealized gain.

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

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

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