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Securities - Summary of Amortized Costs and Fair Values of Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Securities available for sale:
Amortized Cost	$ 96,129	$ 90,594
Gross Unrealized Gains	81	153
Gross Unrealized (Losses)	(2,511)	(1,492)
Fair Value	93,699	89,255
Securities held to maturity:
Amortized Cost	46,791	48,208
Gross Unrealized Gains	18	90
Gross Unrealized (Losses)	(1,179)	(596)
Fair Value	45,630	47,702	[1]
Total securities, Amortized cost	142,920	138,802
Total securities, Gross unrealized gains	99	243
Total securities, Gross unrealized (losses)	(3,690)	(2,088)
Total securities, Fair value	139,329	136,957
U.S. agency and mortgage-backed securities
Securities available for sale:
Amortized Cost	81,309	76,074
Gross Unrealized Gains	24	67
Gross Unrealized (Losses)	(2,225)	(1,337)
Fair Value	79,108	74,804
Securities held to maturity:
Amortized Cost	30,750	32,149
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(984)	(551)
Fair Value	29,766	31,598
Obligations of states and political subdivisions
Securities available for sale:
Amortized Cost	14,820	14,520
Gross Unrealized Gains	57	86
Gross Unrealized (Losses)	(286)	(155)
Fair Value	14,591	14,451
Securities held to maturity:
Amortized Cost	14,541	14,559
Gross Unrealized Gains	18	74
Gross Unrealized (Losses)	(192)	(45)
Fair Value	14,367	14,588
Corporate debt securities
Securities held to maturity:
Amortized Cost	1,500	1,500
Gross Unrealized Gains	0	16
Gross Unrealized (Losses)	(3)	0
Fair Value	$ 1,497	$ 1,516
[1] Derived from audited consolidated financial statements.

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