Loans - Summary of Information on Non-accrual Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Non Performing Loans [Line Items]
Total non-accrual loans	$ 1,475	$ 1,555
Total non-accrual loans to total loans	0.45%	0.42%
Total non-accrual loans to total assets	0.33%	0.32%
Commercial Land [Member]
Non Performing Loans [Line Items]
Total non-accrual loans		$ 303
Commercial Loan Other [Member]
Non Performing Loans [Line Items]
Total non-accrual loans		16
Residential Real Estate First Mortgages [Member]
Non Performing Loans [Line Items]
Total non-accrual loans	$ 1,266	1,066
Consumer Home Equity and Lines of Credit [Member]
Non Performing Loans [Line Items]
Total non-accrual loans	$ 209	$ 170