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, 2016	Dec. 31, 2015	Dec. 31, 2014
Change in benefit obligation:
Benefit obligation at beginning of year	$ 24,556	$ 27,353	$ 24,768
Interest cost	861	984	1,092
Actuarial loss/(gain)	5,259	(702)	3,680
Benefits paid	(529)	(1,723)	(468)
Foreign currency translation	(4,682)	(1,356)	(1,719)
Benefit obligation at end of year	25,465	24,556	27,353
Change in plan assets:
Fair value of plan assets at beginning of year	24,202	24,968	23,162
Actual return on plan assets	3,116	309	1,821
Employer contributions	1,730	1,946	2,025
Benefits paid	(529)	(1,723)	(468)
Foreign currency translation	(4,501)	(1,298)	(1,572)
Fair value of plan assets at end of year	24,018	24,202	24,968
Funded status at end of year	(1,447)	(354)	(2,385)
Net actuarial loss/(gain) recognized in other comprehensive loss	$ 2,649	$ (727)	$ 2,449