Employee Benefit Obligations - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Net Periodic Benefit Cost
Service cost	$ 820	$ 878
Interest cost (income)	69	62
Expected return on plan assets	(54)	(42)
Amortization of prior service costs	65	124
Amortization of transition obligation	(18)	14
Total net periodic benefit cost	$ 882	$ 1,036
Weighted average assumptions:
Discount rate as of December 31	0.90%	0.60%
Expected long-term rate of return on assets	0.90%	0.60%
Rate of compensation increase	1.00%	1.00%
Mortality and disability assumptions	BVG 2015 GT	BVG 2015 GT