Employee benefit obligations - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Net Periodic Benefit Cost
Service cost	$ 1,915	$ 1,483
Interest cost (income)	48	37
Expected return on plan assets	(508)	(31)
Amortization of actuarial (gain) loss	133	120
Amortization of prior service costs	(94)	(21)
Total net periodic benefit cost	$ 1,494	$ 1,588
Weighted average assumptions:
Discount rate as of December 31	0.20%	0.20%
Expected long-term rate of return on assets	2.50%	0.20%
Rate of compensation increase	1.00%	1.00%