Employee benefit obligations - Net Funded Status (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Change in Benefit Obligation
Projected benefit obligation at beginning of year	$ 29,975	$ 22,753
Interest cost	$ 62	$ 48
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax
Company service cost	$ 2,725	$ 1,915
Employee contributions	1,631	1,167
Prior service cost	484	(923)
Benefits paid	423	2,976
Actuarial loss	(5,865)	2,039
Projected benefit obligation at end of year	29,435	29,975
Change in Plan Assets
Fair value of plan assets at beginning of year	25,967	18,082
Actual return on plan assets	(4,937)	1,992
Employer contributions	2,446	1,750
Employee contributions	1,631	1,167
Benefits paid	424	2,976
Fair value of plan assets at end of year	25,531	25,967
Funded Status at End of year
Excess of obligation over assets	3,904	4,008
Change in Accrued Benefit Liability
Accrued benefit liability at beginning of year	(4,008)	(4,671)
Company contributions made during year	2,446	1,750
Net periodic benefit cost for year	(2,078)	(1,310)
Net decrease (increase) in accumulated other comprehensive loss	(264)	223
Accrued benefit liability at end of year	(3,904)	(4,008)
Non-current plan assets	25,531	25,967
Non-current liability	29,435	29,975
Accrued benefit liability at end of year	(3,904)	(4,008)
Projected Benefit Payments
Projected year 1	539	567
Projected year 2	744	454
Projected year 3	983	819
Projected year 4	1,065	765
Projected year 5	578	452
Projected years 6-10	$ 16,940	$ 13,816