Loans and allowance for credit losses - Additional Information (Details)	3 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2023 USD ($)	Jun. 30, 2023 USD ($) loan	Jun. 30, 2022 USD ($) loan	Dec. 31, 2022 USD ($) loan	Mar. 31, 2023 USD ($)	Jan. 01, 2023 USD ($)	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan amount				$ 535,645,000
Defaults on TDRs that were modified as TDRs | loan		0	0
Provision for (recovery of) credit losses			$ (400,000)	(300,000)
Loans and leases receivable, allowance			3,423,000	$ 3,370,000			$ 3,403,000	$ 3,423,000
Total Allowance for credit losses	$ 3,530,000	$ 3,530,000
Total Allowance for credit losses	3,256,000	3,256,000			$ 3,272,000
Allowance for credit losses on unfunded credit exposure	277,000	277,000
Interest on non accrual loans		13,000
Number of Loans | loan				24
Provision for credit losses for loans	(22,000)	$ 1,000	$ (400,000)
Loan growth being offset by improved credit metrics as non-performing loans as a percentage of loans		0.06%		0.13%
Recovery for credit losses for unfunded commitments	22,000	$ (1,000)
Adoption of ASC 326
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, allowance				$ (127,000)
Accounting Standards Update 2016-13 | Adoption of ASC 326
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Allowance for credit losses						$ 150,000
Total Allowance for credit losses						(127,000)
Allowance for credit losses on unfunded credit exposure						277,000
Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjusted Balance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Allowance for credit losses						3,520,000
Total Allowance for credit losses						3,243,000
Allowance for credit losses on unfunded credit exposure						$ 277,000
Asset Pledged as Collateral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged as collateral	$ 36,705,000	$ 36,705,000		$ 33,706,000
Guaranteed student loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage Of Recovery Loss On Portfolio From Historical Experience	98.00%	98.00%
United States Department of Agriculture Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percent of guarantee for principal and interest on financing receivable		100.00%