Loans - Recorded Investment for Past Due and Non-accruing Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	$ 5,095	$ 5,021
90 Days or More Past Due and Still Accruing	214	213
Nonaccruals	6,892	6,496
Total Past Due and Nonaccruals	12,201	11,730
Current	778,459	754,566
Total Loans	790,660	766,296
Construction, Land and Land Development
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	153	261
Nonaccruals	1,090	1,237
Total Past Due and Nonaccruals	1,243	1,498
Current	71,617	64,544
Total Loans	72,860	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	800	875
Total Loans	800	923
Commercial Mortgages (Non-Owner Occupied)
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due		449
Nonaccruals	447
Total Past Due and Nonaccruals	447	449
Current	148,759	146,308
Total Loans	149,206	146,757
Commercial Mortgages (Owner Occupied)
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	219	573
90 Days or More Past Due and Still Accruing	127
Nonaccruals	1,809	1,752
Total Past Due and Nonaccruals	2,155	2,325
Current	76,985	77,727
Total Loans	79,140	80,052
Residential First Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	4,305	2,670
90 Days or More Past Due and Still Accruing	67	141
Nonaccruals	1,987	1,942
Total Past Due and Nonaccruals	6,359	4,753
Current	270,683	264,612
Total Loans	277,042	269,365
Residential Revolving and Junior Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	13	449
90 Days or More Past Due and Still Accruing	20	20
Nonaccruals	1,342	1,338
Total Past Due and Nonaccruals	1,375	1,807
Current	44,001	44,691
Total Loans	45,376	46,498
Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	101	331
Nonaccruals	101	92
Total Past Due and Nonaccruals	202	423
Current	129,023	113,670
Total Loans	129,225	114,093
Consumer and Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	304	288
90 Days or More Past Due and Still Accruing		4
Nonaccruals	116	135
Total Past Due and Nonaccruals	420	427
Current	36,591	42,139
Total Loans	$ 37,011	$ 42,566