Loans - Composition of Nonaccrual Loans and Impaired Loans (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Disclosure [Abstract]
Loans on nonaccrual	$ 3,996,000	$ 2,014,000	$ 1,313,000
Loans 90 days past due and still accruing	90,000	0	0
Impaired loans on nonaccrual included above	3,178,000	891,000	296,000
Total recorded investment in impaired loans	5,379,000	3,252,000	3,051,000
Average recorded investment of impaired loans	3,641,000	3,161,000	5,491,000
Accruing troubled debt restructures	2,202,000	2,361,000	2,559,000
Interest income not recorded on nonaccrual loans according to their original terms	95,000	67,000	64,000
Interest income on nonaccrual loans actually recorded	0	0	0
Interest income recognized on impaired loans	$ 94,000	$ 103,000	$ 196,000