Summary of significant accounting policies - Recent accounting standards (Details) - USD ($) $ in Thousands	Jan. 01, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Loans and leases
Ending balance		$ 21,895
Off-balance sheet exposures		43	$ 179	$ 137	$ 122
Impact to retained earnings		248,550	230,515
Stockholders' equity		340,422	315,350	$ 340,126	$ 316,877
Commercial
Loans and leases
Ending balance		2,272
Commercial real estate
Loans and leases
Ending balance		14,153
Residential real estate
Loans and leases
Ending balance		3,782
Consumer
Loans and leases
Ending balance		900
Cumulative impact of adoption
Loans and leases
Off-balance sheet exposures		$ 270
Accounting Standards Update 2016-13 | Cumulative impact of adoption
Error Corrections and Prior Period Adjustments Restatement
Decreased of ACL related to loans offset to unfunded loan commitments	$ 3,300
Loans and leases
Ending balance	$ 3,000		24,189
Stockholders' equity			2,364
Accounting Standards Update 2016-13 | Cumulative impact of adoption | Commercial
Loans and leases
Ending balance			2,682
Accounting Standards Update 2016-13 | Cumulative impact of adoption | Commercial real estate
Loans and leases
Ending balance			14,571
Accounting Standards Update 2016-13 | Cumulative impact of adoption | Residential real estate
Loans and leases
Ending balance			4,039
Accounting Standards Update 2016-13 | Cumulative impact of adoption | Consumer
Loans and leases
Ending balance			$ 903