Loans - Allowances for Loan Losses and Ending Balances by Portfolio Segment and Based on Impairment Method (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	$ 609	$ 389
Collectively evaluated for impairment	4,396	4,273
Total ending allowance balance	5,005	4,662	$ 4,494	$ 4,381
Loans:
Loans individually evaluated for impairment	8,270	8,724
Loans collectively evaluated for impairment	424,715	413,689
Total ending loans balance	432,985	422,413
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	583	299
Collectively evaluated for impairment	1,470	1,365
Total ending allowance balance	2,053	1,664	1,394	1,289
Loans:
Loans individually evaluated for impairment	6,017	6,127
Loans collectively evaluated for impairment	122,907	117,016
Total ending loans balance	128,924	123,143
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment		64
Collectively evaluated for impairment	1,225	1,207
Total ending allowance balance	1,225	1,271	1,574	1,524
Loans:
Loans individually evaluated for impairment	744	1,064
Loans collectively evaluated for impairment	152,264	147,711
Total ending loans balance	153,008	148,775
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	26	26
Collectively evaluated for impairment	1,058	1,060
Total ending allowance balance	1,084	1,086	1,003	1,039
Loans:
Loans individually evaluated for impairment	1,509	1,533
Loans collectively evaluated for impairment	125,590	124,242
Total ending loans balance	127,099	125,775
Construction & Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Collectively evaluated for impairment	106	123
Total ending allowance balance	106	123	133	142
Loans:
Loans collectively evaluated for impairment	13,571	15,452
Total ending loans balance	13,571	15,452
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Collectively evaluated for impairment	94	86
Total ending allowance balance	94	86	69	60
Loans:
Loans collectively evaluated for impairment	10,383	9,268
Total ending loans balance	10,383	9,268
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Collectively evaluated for impairment	443	432
Total ending allowance balance	$ 443	$ 432	$ 321	$ 327