Off balance sheet financial instruments - Summary of Contractual Amounts of Off-balance Sheet Commitments (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Off balance sheet financial instruments
Commitments to extend credit	$ 435,015	$ 553,337
Unused portions of lines of credit	90,407	78,406
Standby letters of credit	62,155	57,626
Total contractual amounts of off-balance sheet commitments	$ 587,577	$ 689,369