Other Employee Benefit Plans (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in benefit obligation:
Benefit obligation at January 1	$ 11,419	$ 11,426
Service costs	0	0	$ 156
Interest costs	386	397	353
Actuarial loss (gain)	(1,720)	177
Benefits paid	310	312
Foreign currency exchange changes	374	(269)
Benefit obligation at December 31	10,149	11,419	$ 11,426
Fair value of plan assets at December 31	0	0
Unfunded status at December 31	10,149	11,419
Amounts recognized in the Consolidated Balance Sheets:
Current liabilities	6,262	292
Non-current liabilities	3,887	$ 11,127
Supplemental Executive Retirement Plan (SERP)
Change in benefit obligation:
Actuarial loss (gain)	$ 1,700
Net periodic benefit cost:
Discount rate	4.00%	4.00%
Rate of increase in compensation levels	3.00%	3.00%
Funded status and projected benefit obligation:
Discount rate	2.75%	4.00%
Rate of increase in compensation levels	0.00%	3.00%
Defined benefit pension plan for employees outside the United States
Net periodic benefit cost:
Discount rate	2.00%	2.00%
Funded status and projected benefit obligation:
Discount rate	1.75%	2.00%