Income taxes - Reconciliation of Effective Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income taxes
Provision for income tax at statutory rate	$ 6,825	$ 9,527	$ 11,239
State tax, net of federal benefit	(397)	(216)	(475)
Tax exempt interest	(1,057)	(1,400)	(1,194)
Bank owned life insurance income	(221)	(205)	(119)
Residential housing program tax credits	(755)	(911)	(1,091)
Nondeductible transaction costs	179
Other, net	(247)	49	688
Total income tax expense	$ 5,121	$ 7,276	$ 9,998
Provision for income tax at statutory rate	21.00%	21.00%	21.00%
State tax, net of federal benefit	1.22%	0.63%	0.89%
Tax exempt interest	(3.25%)	(3.09%)	(2.23%)
Bank owned life insurance income	(0.68%)	(0.45%)	(0.22%)
Residential housing program tax credits	(2.32%)	(2.01%)	(2.04%)
Nondeductible transaction costs	0.55%
Other, net	(0.76%)	(0.04%)	1.29%
Total	15.76%	16.04%	18.69%