Loans and allowance for loan losses - Additional information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses, after ASU 2016-13	$ 150,000
Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest	3,574,000	$ 3,270,000	$ 3,423,000	$ 3,370,000
Total Allowance for credit losses	3,890,000	3,530,000
Total Allowance for credit losses	3,574,000	3,270,000	3,423,000	$ 3,370,000
Allowance for credit losses on unfunded credit exposure	320,000	254,000
Interest on non accrual loans	7,000
Provision for credit losses for loans	$ 136,700	$ 23,000
Loan growth being offset by improved credit metrics as non-performing loans as a percentage of loans	0.05%	0.12%
Recovery for credit losses for unfunded commitments	$ 13,300	$ (23,000)
Allowance for credit losses on loans to total loans ratio	0.60
Peer average allowance for credit losses on loans to total loans ratio	1.11
Asset Pledged as Collateral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged as collateral	$ 54,800,000		$ 35,500,000
Guaranteed student loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage Of Recovery Loss On Portfolio From Historical Experience	98.00%