Loans - Additional Information (Detail)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($) Loan Property	Sep. 30, 2019 Loan	Sep. 30, 2020 USD ($) Loan Contract Property	Sep. 30, 2019 Contract	Dec. 31, 2019 USD ($) Contract
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans serviced for others	$ 105,800,000		$ 105,800,000		$ 95,700,000
Concentrations of loans related to a single industry	0		0		0
Assisted living facilities loans	619,729,000		619,729,000		544,616,000
Loans classified as troubled debt restructurings	1,900,000		1,900,000		2,500,000
Reserves allocated to customers whose loan terms are modified in troubled debt restructurings	29,000		29,000		$ 18,000
Loans payable in nonaccrual of interest status	$ 320,000		$ 320,000
Number of loans restructured	0	0	13	1
Loans restructured, subsequently defaulted | Contract			0		1
Loans restructured, subsequently defaulted					$ 200,000
Number of properties acquired | Property	0		0
Other real estate real estate acquired through foreclosure					99,000
Mortgage loans in process of foreclosure amount			$ 21,000		50,000
Other repossessed assets	$ 0		0		$ 20,000
Outstanding balance of commercial loans classified under credit risk, minimum amount	500,000		500,000
Loans listed as not rated under risk category, maximum amount	500,000		500,000
Performing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans classified as troubled debt restructurings	1,600,000		1,600,000
Covid-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance	54,000,000		54,000,000
Business loans	$ 31,000,000		$ 31,000,000
Number of loan granted with second deferral | Loan	1		1
Loans granted with second deferral	$ 34,000		$ 34,000
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
Covid-19 [Member] | Assisted Living Facilities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Assisted living facilities loans	20,000,000		$ 20,000,000
Paycheck Protection Program [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of PPP loans | Loan			793
Principal amount outstanding on PPP loans	$ 92,100,000		$ 92,100,000
PPP loans guaranteed percentage	100.00%		100.00%
Loan processing fee received			$ 3,200,000