Loans - Aging Analysis of Past Due Loans, Segregated by Class (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	$ 6,510	$ 5,549
Total Past Due Loans	7,247	6,689
Current Loans	386,095	387,963
Total Gross Loans	393,342	394,652
Accruing Loans 90 or more Days Past Due	299	209
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	5,607	4,688
Total Past Due Loans	6,026	5,612
Current Loans	315,396	315,048
Total Gross Loans	321,422	320,660
Accruing Loans 90 or more Days Past Due		179
Commercial Real Estate Portfolio Segment [Member] | Land Development And Construction Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	54	208
Total Past Due Loans	54	286
Current Loans	22,288	23,507
Total Gross Loans	22,342	23,793
Commercial Real Estate Portfolio Segment [Member] | Farmland Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	183	584
Total Past Due Loans	214	649
Current Loans	17,822	17,526
Total Gross Loans	18,036	18,175
Commercial Real Estate Portfolio Segment [Member] | 1-4 Family Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	3,338	2,993
Total Past Due Loans	3,571	3,589
Current Loans	93,860	94,223
Total Gross Loans	97,431	97,812
Accruing Loans 90 or more Days Past Due		179
Commercial Real Estate Portfolio Segment [Member] | Real Estate Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	2,032	903
Total Past Due Loans	2,187	1,088
Current Loans	181,426	179,792
Total Gross Loans	183,613	180,880
Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	307	66
Total Past Due Loans	554	252
Current Loans	54,669	54,274
Total Gross Loans	55,223	54,526
Accruing Loans 90 or more Days Past Due	247
Real Estate Loans [Member] | Commercial and Industrial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	254	66
Total Past Due Loans	501	252
Current Loans	53,653	53,509
Total Gross Loans	54,154	53,761
Accruing Loans 90 or more Days Past Due	247
Real Estate Loans [Member] | Farm Production and Other Farm Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	53
Total Past Due Loans	53
Current Loans	1,016	765
Total Gross Loans	1,069	765
Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	596	795
Total Past Due Loans	667	825
Current Loans	16,030	18,641
Total Gross Loans	16,697	19,466
Accruing Loans 90 or more Days Past Due	52	30
Consumer Portfolio Segment [Member] | Credit Card Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	8	7
Total Past Due Loans	9	10
Current Loans	1,193	1,146
Total Gross Loans	1,202	1,156
Accruing Loans 90 or more Days Past Due	1	3
Consumer Portfolio Segment [Member] | Other Consumer Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	588	788
Total Past Due Loans	658	815
Current Loans	14,837	17,495
Total Gross Loans	15,495	18,310
Accruing Loans 90 or more Days Past Due	51	27
Loans 90 or more Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	737	1,140
Loans 90 or more Days Past Due [Member] | Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	419	924
Loans 90 or more Days Past Due [Member] | Commercial Real Estate Portfolio Segment [Member] | Land Development And Construction Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		78
Loans 90 or more Days Past Due [Member] | Commercial Real Estate Portfolio Segment [Member] | Farmland Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	31	65
Loans 90 or more Days Past Due [Member] | Commercial Real Estate Portfolio Segment [Member] | 1-4 Family Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	233	596
Loans 90 or more Days Past Due [Member] | Commercial Real Estate Portfolio Segment [Member] | Real Estate Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	155	185
Loans 90 or more Days Past Due [Member] | Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	247	186
Loans 90 or more Days Past Due [Member] | Real Estate Loans [Member] | Commercial and Industrial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	247	186
Loans 90 or more Days Past Due [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	71	30
Loans 90 or more Days Past Due [Member] | Consumer Portfolio Segment [Member] | Credit Card Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	1	3
Loans 90 or more Days Past Due [Member] | Consumer Portfolio Segment [Member] | Other Consumer Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	$ 70	$ 27