Allowance for Loan Losses - Past Due Information of Loan Portfolio by Class (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable Impaired [Line Items]
Total Past Due Loans	$ 1,921	$ 2,174
Current Loans	366,041	367,796
Total Loans	367,962	369,970
Accruing Loans 90 or More Days Past Due	0	0
Loans 30-89 Days Past Due [Member]
Financing Receivable Impaired [Line Items]
Total Past Due Loans	972	1,130
Loans 90 Days or More Past Due [Member]
Financing Receivable Impaired [Line Items]
Total Past Due Loans	949	1,044
Real Estate - Commercial [Member]
Financing Receivable Impaired [Line Items]
Total Past Due Loans	188	273
Current Loans	130,844	130,361
Total Loans	131,032	130,634
Accruing Loans 90 or More Days Past Due	0	0
Real Estate - Commercial [Member] | Loans 30-89 Days Past Due [Member]
Financing Receivable Impaired [Line Items]
Total Past Due Loans	12
Real Estate - Commercial [Member] | Loans 90 Days or More Past Due [Member]
Financing Receivable Impaired [Line Items]
Total Past Due Loans	176	273
Other Real Estate Construction [Member]
Financing Receivable Impaired [Line Items]
Total Past Due Loans	46	47
Current Loans	28,392	31,094
Total Loans	28,438	31,141
Accruing Loans 90 or More Days Past Due	0	0
Other Real Estate Construction [Member] | Loans 90 Days or More Past Due [Member]
Financing Receivable Impaired [Line Items]
Total Past Due Loans	46	47
Real Estate 1 - 4 Family Construction [Member]
Financing Receivable Impaired [Line Items]
Current Loans	6,625
Total Loans	6,625	7,805
Accruing Loans 90 or More Days Past Due	0
Real Estate - Residential [Member]
Financing Receivable Impaired [Line Items]
Total Past Due Loans	1,289	1,496
Current Loans	77,481	74,908
Total Loans	78,770	76,404
Accruing Loans 90 or More Days Past Due	0	0
Real Estate - Residential [Member] | Loans 30-89 Days Past Due [Member]
Financing Receivable Impaired [Line Items]
Total Past Due Loans	641	890
Real Estate - Residential [Member] | Loans 90 Days or More Past Due [Member]
Financing Receivable Impaired [Line Items]
Total Past Due Loans	648	606
Home Equity [Member]
Financing Receivable Impaired [Line Items]
Total Past Due Loans	232	218
Current Loans	50,637	52,323
Total Loans	50,869	52,541
Accruing Loans 90 or More Days Past Due	0	0
Home Equity [Member] | Loans 30-89 Days Past Due [Member]
Financing Receivable Impaired [Line Items]
Total Past Due Loans	153	100
Home Equity [Member] | Loans 90 Days or More Past Due [Member]
Financing Receivable Impaired [Line Items]
Total Past Due Loans	79	118
Other Loans [Member]
Financing Receivable Impaired [Line Items]
Current Loans	2,004	2,110
Total Loans	2,004	2,110
Accruing Loans 90 or More Days Past Due	0	0
Real Estate Construction [Member]
Financing Receivable Impaired [Line Items]
Current Loans		7,805
Total Loans		7,805
Accruing Loans 90 or More Days Past Due		0
Commercial Loan [Member]
Financing Receivable Impaired [Line Items]
Total Past Due Loans	145	54
Current Loans	57,990	57,122
Total Loans	58,135	57,176
Accruing Loans 90 or More Days Past Due	0	0
Commercial Loan [Member] | Loans 30-89 Days Past Due [Member]
Financing Receivable Impaired [Line Items]
Total Past Due Loans	145	54
Consumer Loans [Member]
Financing Receivable Impaired [Line Items]
Total Past Due Loans	21	86
Current Loans	12,068	12,073
Total Loans	12,089	12,159
Accruing Loans 90 or More Days Past Due	0	0
Consumer Loans [Member] | Loans 30-89 Days Past Due [Member]
Financing Receivable Impaired [Line Items]
Total Past Due Loans	$ 21	$ 86