Loans - Schedule of Allowances for Loan Losses by Portfolio Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 5,454	$ 5,005	$ 5,291	$ 4,662
PROVISION FOR LOAN LOSSES	845	165	685	329
Charge-offs	(34)	(18)	(47)	(28)
Recoveries	24	4	360	193
Net charge-offs	(10)	(14)	313	165
Ending balance	6,289	5,156	6,289	5,156
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,704	2,053	2,207	1,664
PROVISION FOR LOAN LOSSES	675	326	(156)	720
Charge-offs	(32)	(6)	(40)	(15)
Recoveries	15	3	351	7
Net charge-offs	(17)	(3)	311	(8)
Ending balance	2,362	2,376	2,362	2,376
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,538	1,225	1,264	1,271
PROVISION FOR LOAN LOSSES	180	48	454	(180)
Charge-offs		(12)		(12)
Recoveries		1		183
Net charge-offs		(11)		171
Ending balance	1,718	1,262	1,718	1,262
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,303	1,084	1,189	1,086
PROVISION FOR LOAN LOSSES	(47)	11	67	7
Recoveries	8		8	2
Net charge-offs	8		8	2
Ending balance	1,264	1,095	1,264	1,095
Construction & Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	184	106	178	123
PROVISION FOR LOAN LOSSES	38	21	44	4
Ending balance	222	127	222	127
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	165	94	141	86
PROVISION FOR LOAN LOSSES	18	16	47	24
Charge-offs	(2)		(7)	(1)
Recoveries	1		1	1
Net charge-offs	(1)		(6)
Ending balance	182	110	182	110
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	560	443	312	432
PROVISION FOR LOAN LOSSES	(19)	(257)	229	(246)
Ending balance	$ 541	$ 186	$ 541	$ 186