Commitments and contingencies - Contingencies (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2020 USD ($)
Loss Contingency Accrual [Roll Forward]
Contingencies accrual, beginning balance	$ 6,385
Increase	228
Provision used	(828)
Provision released not used*	(2,116)
Currency translation adjustments	(80)
Other	(2,629)
Contingencies accrual, ending balance	960
Contingencies accrual, of which current	960
Provision for employee-related litigation
Loss Contingency Accrual [Roll Forward]
Contingencies accrual, beginning balance	620
Increase	228
Provision used	(5)
Provision released not used*	0
Currency translation adjustments	32
Other	0
Contingencies accrual, ending balance	875
Contingencies accrual, of which current	875
Other provisions
Loss Contingency Accrual [Roll Forward]
Contingencies accrual, beginning balance	5,765
Increase	0
Provision used	(823)
Provision released not used*	(2,116)
Currency translation adjustments	(112)
Other	(2,629)
Contingencies accrual, ending balance	85
Contingencies accrual, of which current	$ 85