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Securities - Summary of Amortized Costs and Fair Values of Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Securities available for sale:
Amortized Cost	$ 109,496	$ 90,594
Gross Unrealized Gains	67	153
Gross Unrealized (Losses)	(2,856)	(1,492)
Fair Value	106,707	89,255
Securities held to maturity:
Amortized Cost	45,701	48,208
Gross Unrealized Gains	17	90
Gross Unrealized (Losses)	(1,302)	(596)
Fair Value	44,416	47,702	[1]
Total securities, Amortized cost	155,197	138,802
Total securities, Gross unrealized gains	84	243
Total securities, Gross unrealized (losses)	(4,158)	(2,088)
Total securities, Fair value	151,123	136,957
U.S. agency and mortgage-backed securities
Securities available for sale:
Amortized Cost	94,387	76,074
Gross Unrealized Gains	21	67
Gross Unrealized (Losses)	(2,580)	(1,337)
Fair Value	91,828	74,804
Securities held to maturity:
Amortized Cost	29,678	32,149
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(1,111)	(551)
Fair Value	28,567	31,598
Obligations of states and political subdivisions
Securities available for sale:
Amortized Cost	15,109	14,520
Gross Unrealized Gains	46	86
Gross Unrealized (Losses)	(276)	(155)
Fair Value	14,879	14,451
Securities held to maturity:
Amortized Cost	14,523	14,559
Gross Unrealized Gains	17	74
Gross Unrealized (Losses)	(189)	(45)
Fair Value	14,351	14,588
Corporate debt securities
Securities held to maturity:
Amortized Cost	1,500	1,500
Gross Unrealized Gains	0	16
Gross Unrealized (Losses)	(2)	0
Fair Value	$ 1,498	$ 1,516
[1] Derived from audited consolidated financial statements.

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