Employee Benefit Obligations - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Net Periodic Benefit Cost
Service cost	$ 878	$ 498
Interest cost (income)	62	(21)
Expected return on plan assets	(42)	(49)
Amortization of prior service costs	124	87
Amortization of transition obligation	14	14
Total net periodic benefit cost	$ 1,036	$ 529
Weighted average assumptions:
Discount rate as of December 31	0.60%	0.60%
Expected long-term rate of return on assets	0.60%	0.60%
Rate of compensation increase	1.00%	1.00%
Mortality and disability assumptions	BVG 2015 GT	BVG 2015 GT