Employee benefit plans - Summary of Pension and Postretirement Life Insurance Plans (Details) - Pension Benefits - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Change in benefit obligation:
Benefit obligation, beginning	$ 13,792	$ 18,066
Interest cost	655	456	$ 419
Change in experience gain	2	26
Change in actuarial assumptions	306	(3,899)
Benefits paid	(910)	(857)
Benefit obligation, ending	13,845	13,792	18,066
Change in plan assets:
Fair value of plan assets, beginning	16,106	19,257
Actual return on plan assets	2,413	(2,294)
Benefits paid	(910)	(857)
Fair value of plan assets, ending	17,609	16,106	$ 19,257
Funded status at end of year	$ 3,764	$ 2,314