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Securities - Summary of Amortized Costs and Fair Values of Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Securities available for sale:
Amortized Cost	$ 93,485	$ 96,106
Gross Unrealized Gains	452	333
Gross Unrealized (Losses)	(835)	(1,637)
Fair Value	93,102	94,802	[1]
Securities held to maturity:
Amortized Cost	49,376	53,398
Gross Unrealized Gains	287	19
Gross Unrealized (Losses)	(247)	(708)
Fair Value	49,416	52,709	[1]
Total securities, Amortized cost	142,861	149,504
Total securities, Gross unrealized gains	739	352
Total securities, Gross unrealized (losses)	(1,082)	(2,345)
Total securities, Fair value	142,518	147,511
U.S. agency and mortgage-backed securities
Securities available for sale:
Amortized Cost	78,039	81,451
Gross Unrealized Gains	235	177
Gross Unrealized (Losses)	(767)	(1,457)
Fair Value	77,507	80,171
Securities held to maturity:
Amortized Cost	33,300	37,269
Gross Unrealized Gains	48	1
Gross Unrealized (Losses)	(234)	(483)
Fair Value	33,114	36,787
Obligations of states and political subdivisions
Securities available for sale:
Amortized Cost	15,445	14,654
Gross Unrealized Gains	203	146
Gross Unrealized (Losses)	(68)	(180)
Fair Value	15,580	14,620
Securities held to maturity:
Amortized Cost	14,576	14,629
Gross Unrealized Gains	239	18
Gross Unrealized (Losses)	(1)	(211)
Fair Value	14,814	14,436
Corporate equity securities
Securities available for sale:
Amortized Cost	1	1
Gross Unrealized Gains	14	10
Gross Unrealized (Losses)	0	0
Fair Value	15	11
Corporate debt securities
Securities held to maturity:
Amortized Cost	1,500	1,500
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(12)	(14)
Fair Value	$ 1,488	$ 1,486
[1] Derived from audited consolidated financial statements.

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