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Employee benefit plans - Summary of Pension and Postretirement Life Insurance Plans (Details) - Pension Benefits - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Change in benefit obligation:      
Benefit obligation, beginning $ 19,113 $ 17,491  
Interest cost 419 544 $ 639
Change in experience gain (49) (291)  
Change in actuarial assumptions loss (603) 2,159  
Benefits paid (814) (790)  
Benefit obligation, ending 18,066 19,113 17,491
Change in plan assets:      
Fair value of plan assets, beginning 17,628 16,930  
Actual return on plan assets 2,443 1,488  
Benefits paid (814) (790)  
Fair value of plan assets, ending 19,257 17,628 $ 16,930
Funded status at end of year $ 1,191 $ (1,485)