Loans - Schedule of Analysis of Past due Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Loans, Notes and Certificates, and Loan Servicing Rights [Line Items]
Current Loans	$ 310,433	$ 370,495
Total Loans	312,370	372,589
Non-accrual Loans	$ 2,013	$ 1,555
Total non-accrual loans to total loans	0.64%	0.42%
Total non-accrual loans to total assets	0.47%	0.32%
Loans Past Due 30-89 Days [Member]
Loans, Notes and Certificates, and Loan Servicing Rights [Line Items]
Past Due	$ 1,220	$ 1,687
Loans Past Due 90+ Days [Member]
Loans, Notes and Certificates, and Loan Servicing Rights [Line Items]
Past Due	717	407
Commercial Real Estate [Member]
Loans, Notes and Certificates, and Loan Servicing Rights [Line Items]
Current Loans	178,702	191,645
Total Loans	178,882	191,645
Non-accrual Loans	180
Commercial Real Estate [Member] | Loans Past Due 90+ Days [Member]
Loans, Notes and Certificates, and Loan Servicing Rights [Line Items]
Past Due	180
Commercial Land Development [Member]
Loans, Notes and Certificates, and Loan Servicing Rights [Line Items]
Current Loans	1,623	1,884
Total Loans	1,623	2,187
Non-accrual Loans		303
Commercial Land Development [Member] | Loans Past Due 90+ Days [Member]
Loans, Notes and Certificates, and Loan Servicing Rights [Line Items]
Past Due		303
Commercial Other [Member]
Loans, Notes and Certificates, and Loan Servicing Rights [Line Items]
Current Loans	33,924	30,508
Total Loans	34,072	30,508
Non-accrual Loans		16
Commercial Other [Member] | Loans Past Due 30-89 Days [Member]
Loans, Notes and Certificates, and Loan Servicing Rights [Line Items]
Past Due	148
Residential Real Estate First Mortgages
Loans, Notes and Certificates, and Loan Servicing Rights [Line Items]
Current Loans	63,854	106,523
Total Loans	65,450	108,084
Non-accrual Loans	1,690	1,066
Residential Real Estate First Mortgages | Loans Past Due 30-89 Days [Member]
Loans, Notes and Certificates, and Loan Servicing Rights [Line Items]
Past Due	1,059	1,470
Residential Real Estate First Mortgages | Loans Past Due 90+ Days [Member]
Loans, Notes and Certificates, and Loan Servicing Rights [Line Items]
Past Due	537	91
Residential Real Estate Construction
Loans, Notes and Certificates, and Loan Servicing Rights [Line Items]
Current Loans	2,041	2,097
Total Loans	2,041	2,097
Consumer Home Equity and Lines of Credit [Member]
Loans, Notes and Certificates, and Loan Servicing Rights [Line Items]
Current Loans	29,678	35,926
Total Loans	29,691	36,154
Non-accrual Loans	143	170
Consumer Home Equity and Lines of Credit [Member] | Loans Past Due 30-89 Days [Member]
Loans, Notes and Certificates, and Loan Servicing Rights [Line Items]
Past Due	13	215
Consumer Home Equity and Lines of Credit [Member] | Loans Past Due 90+ Days [Member]
Loans, Notes and Certificates, and Loan Servicing Rights [Line Items]
Past Due		13
Consumer And Other
Loans, Notes and Certificates, and Loan Servicing Rights [Line Items]
Current Loans	611	1,912
Total Loans	$ 611	1,914
Consumer And Other | Loans Past Due 30-89 Days [Member]
Loans, Notes and Certificates, and Loan Servicing Rights [Line Items]
Past Due		$ 2