Loans - Recorded Investment for Past Due and Non-accruing Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	$ 2,567	$ 5,021
90 Days or More Past Due and Still Accruing	129	213
Nonaccruals	4,204	6,496
Total Past Due and Nonaccruals	6,900	11,730
Current	847,459	754,566
Total Loans	854,359	766,296
Construction, land and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	112	261
Nonaccruals	499	1,237
Total Past Due and Nonaccruals	611	1,498
Current	94,139	64,544
Total Loans	94,750	66,042
Farmland
Accounts, Notes, Loans and Financing Receivable [Line Items]
90 Days or More Past Due and Still Accruing		48
Total Past Due and Nonaccruals		48
Current	748	875
Total Loans	748	923
Commercial mortgages (non-owner occupied)
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due		449
Nonaccruals	1,003
Total Past Due and Nonaccruals	1,003	449
Current	170,993	146,308
Total Loans	171,996	146,757
Commercial mortgages (owner occupied)
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	539	573
90 Days or More Past Due and Still Accruing	28
Nonaccruals	1,120	1,752
Total Past Due and Nonaccruals	1,687	2,325
Current	80,704	77,727
Total Loans	82,391	80,052
Residential first mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	1,342	2,670
90 Days or More Past Due and Still Accruing	78	141
Nonaccruals	1,092	1,942
Total Past Due and Nonaccruals	2,512	4,753
Current	290,754	264,612
Total Loans	293,266	269,365
Residential revolving and junior mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	119	449
90 Days or More Past Due and Still Accruing	20	20
Nonaccruals	385	1,338
Total Past Due and Nonaccruals	524	1,807
Current	38,646	44,691
Total Loans	39,170	46,498
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	98	331
Nonaccruals	48	92
Total Past Due and Nonaccruals	146	423
Current	143,972	113,670
Total Loans	144,118	114,093
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	357	288
90 Days or More Past Due and Still Accruing	3	4
Nonaccruals	57	135
Total Past Due and Nonaccruals	417	427
Current	27,503	42,139
Total Loans	$ 27,920	$ 42,566