Loans - Schedule of Allowances for Loan Losses by Portfolio Segment (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 4,662	$ 4,381
Provision for possible loan losses	164	194
Charge-offs	(10)	(109)
Recoveries	189	28
Net (charge-offs) recoveries	179	(81)
Ending balance	5,005	4,494
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,664	1,289
Provision for possible loan losses	394	101
Charge-offs	(9)	(2)
Recoveries	4	6
Net (charge-offs) recoveries	(5)	4
Ending balance	2,053	1,394
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,271	1,524
Provision for possible loan losses	(228)	64
Charge-offs		(24)
Recoveries	182	10
Net (charge-offs) recoveries	182	(14)
Ending balance	1,225	1,574
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,086	1,039
Provision for possible loan losses	(4)	8
Charge-offs		(53)
Recoveries	2	9
Net (charge-offs) recoveries	2	(44)
Ending balance	1,084	1,003
Construction & Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	123	142
Provision for possible loan losses	(17)	(9)
Ending balance	106	133
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	86	60
Provision for possible loan losses	8	36
Charge-offs	(1)	(30)
Recoveries	1	3
Net (charge-offs) recoveries		(27)
Ending balance	94	69
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	432	327
Provision for possible loan losses	11	(6)
Ending balance	$ 443	$ 321