Loans - Schedule of Allowances for Loan Losses by Portfolio Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 6,289	$ 5,156	$ 5,291	$ 4,662
PROVISION FOR LOAN LOSSES	280	164	965	493
Charge-offs	(1,138)	(346)	(1,185)	(374)
Recoveries	5	28	365	221
Net charge-offs	(1,133)	(318)	(820)	(153)
Ending balance	5,436	5,002	5,436	5,002
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	2,362	2,376	2,207	1,664
PROVISION FOR LOAN LOSSES	881	77	725	797
Charge-offs	(1,138)	(261)	(1,178)	(276)
Recoveries	4	27	355	34
Net charge-offs	(1,134)	(234)	(823)	(242)
Ending balance	2,109	2,219	2,109	2,219
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,718	1,262	1,264	1,271
PROVISION FOR LOAN LOSSES	(88)	63	366	(117)
Charge-offs		(38)		(50)
Recoveries				183
Net charge-offs		(38)		133
Ending balance	1,630	1,287	1,630	1,287
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,264	1,095	1,189	1,086
PROVISION FOR LOAN LOSSES	(53)	50	14	57
Recoveries		1	8	3
Net charge-offs		1	8	3
Ending balance	1,211	1,146	1,211	1,146
Construction & Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	222	127	178	123
PROVISION FOR LOAN LOSSES	21	24	65	28
Ending balance	243	151	243	151
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	182	110	141	86
PROVISION FOR LOAN LOSSES	(5)	74	42	98
Charge-offs		(47)	(7)	(48)
Recoveries	1		2	1
Net charge-offs	1	(47)	(5)	(47)
Ending balance	178	137	178	137
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	541	186	312	432
PROVISION FOR LOAN LOSSES	(476)	(124)	(247)	(370)
Ending balance	$ 65	$ 62	$ 65	$ 62