Employee benefit obligations - Net Funded Status (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Change in Benefit Obligation
Projected benefit obligation at beginning of year	$ 51,057	$ 29,435
Interest cost	$ 703	$ 850
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	$ 4,202	$ 2,992
Employee contributions	2,683	2,517
Prior service cost	0	(768)
Benefits paid	2,772	6,726
Actuarial loss	(62)	9,305
Projected benefit obligation at end of year	61,355	51,057
Change in Plan Assets
Fair value of plan assets at beginning of year	43,250	25,531
Actual return on plan assets	2,120	4,699
Employer contributions	3,991	3,776
Employee contributions	2,683	2,518
Benefits paid	2,772	6,726
Fair value of plan assets at end of year	54,816	43,250
Funded Status at End of year
Excess of obligation over assets	6,539	7,807
Change in Accrued Benefit Liability
Accrued benefit liability at beginning of year	(7,807)	(3,904)
Company contributions made during year	3,991	3,776
Net periodic benefit cost for year	(3,308)	(3,058)
Net decrease (increase) in accumulated other comprehensive loss	585	(4,621)
Accrued benefit liability at end of year	(6,539)	(7,807)
Non-current plan assets	54,816	43,250
Non-current liability	61,355	51,057
Accrued benefit liability at end of year	(6,539)	(7,807)
Projected Benefit Payments
Projected year 1	1,204	1,138
Projected year 2	1,540	1,102
Projected year 3	1,849	1,546
Projected year 4	966	1,577
Projected year 5	1,748	958
Projected years 6-10	$ 24,374	$ 20,127