Loans - Additional Information (Detail)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2022 USD ($) Industry Property	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($) Loan Industry Contract Property	Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($) Loan Contract Property
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans serviced for others	$ 139,200,000		$ 139,200,000		$ 142,100,000
Interest and fee income on loans	6,680,000	$ 6,897,000	18,489,000	$ 19,993,000
Concentration loans	609,710,000		609,710,000		549,050,000
Assisted living facilities loans	602,963,000		602,963,000		541,536,000
Loans classified as troubled debt restructurings	962,000		962,000		1,300,000
Reserves allocated to customers whose loan terms are modified in troubled debt restructurings	5,000		5,000		$ 14,000
Loans payable classified as nonaccrual	$ 29,000		$ 29,000
Loans restructured, subsequently defaulted | Contract			0		0
Number of properties acquired | Property	0		0		0
Mortgage loans in process of foreclosure amount			$ 17,000		$ 0
Other repossessed assets	$ 0		0		$ 0
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	932,000		932,000
Covid-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance including commitments	37,900,000		37,900,000
Business loans	27,800,000		27,800,000
Covid-19 [Member] | Assisted Living Facilities [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Assisted living facilities loans	$ 10,100,000		$ 10,100,000
Credit Concentration Risk [Member] | Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of industries for credit concentrations | Industry	2		2
Credit Concentration Risk [Member] | Loans Receivable [Member] | Lessors of Non-residential Buildings or Dwellings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration loans	$ 71,900,000		$ 71,900,000
Concentration of credit percentage of total loans			12.00%
Credit Concentration Risk [Member] | Loans Receivable [Member] | Assisted Living Facilities for Elderly [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration loans	27,800,000		$ 27,800,000
Concentration of credit percentage of total loans			5.00%
Paycheck Protection Program [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of PPP loans | Loan			7		76
Principal amount outstanding on PPP loans	$ 392,000		$ 392,000		$ 4,600,000
PPP loans guaranteed percentage	100.00%		100.00%
Loan processing fee received			$ 5,400,000
Remaining unearned fees on loans outstanding	$ 8,000		8,000
Interest and fee income on loans	$ 25,000	$ 974,000	$ 187,000	$ 2,700,000