Pensions - Schedule of changes in the benefit obligation, plan assets and funded status of the plan (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in benefit obligation:
Benefit obligation at beginning of year	$ 28,882	$ 25,465	$ 24,556
Interest cost	705	713	861
Actuarial loss/(gain)	(2,027)	663	5,259
Benefits paid	(556)	(485)	(529)
Foreign currency translation	(1,627)	2,526	(4,682)
Benefit obligation at end of year	25,377	28,882	25,465
Change in plan assets:
Fair value of plan assets at beginning of year	28,232	24,018	24,202
Actual return on plan assets	(1,013)	1,264	3,116
Employer contributions	527	1,009	1,730
Benefits paid	(556)	(485)	(529)
Foreign currency translation	(1,626)	2,426	(4,501)
Fair value of plan assets at end of year	25,564	28,232	24,018
Funded status at end of year	187	(650)	(1,447)
Net actuarial (gain)/loss recognized in other comprehensive loss	$ (689)	$ (383)	$ 2,649