Loans - Additional Information (Detail)	6 Months Ended		12 Months Ended
	Jun. 30, 2020 USD ($) Loan Contract Property	Jun. 30, 2019 USD ($) Contract	Dec. 31, 2019 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans serviced for others	$ 96,700,000		$ 95,700,000
Concentrations of loans related to a single industry	0		0
Loans classified as troubled debt restructurings	2,400,000		2,500,000
Reserves allocated to customers whose loan terms are modified in troubled debt restructurings	31,000		18,000
Loans payable in nonaccrual of interest status	$ 327,000
Loans restructured, subsequently defaulted | Contract	0	1
Loans restructured, subsequently defaulted		$ 200,000
Number of properties acquired | Property	1
Other real estate real estate acquired through foreclosure	$ 98,000		99,000
Mortgage loans in process of foreclosure amount	61,000		50,000
Other repossessed assets	0		$ 0
Outstanding balance of commercial loans classified under credit risk, minimum amount	500,000
Loans listed as not rated under risk category, maximum amount	500,000
Performing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans classified as troubled debt restructurings	2,100,000
Covid-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	36,200,000
Business loans	$ 31,600,000
Covid-19 [Member] | Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term of principal and interest payments deferred	3 months
Covid-19 [Member] | Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term of principal and interest payments deferred	4 months
Paycheck Protection Program [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of PPP loans | Loan	752
Principal amount outstanding on PPP loans	$ 91,100,000
PPP loans guaranteed percentage	100.00%
Loan processing fee received	$ 3,200,000