Defined Benefit Pension Plans Change in Benefit Obligation and Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at January 1,	$ 97,261	$ 98,767
Service cost	3,968	3,472	$ 4,572
Interest cost	2,264	2,573	2,380
Actuarial (gain) loss	(2,351)	7,733
Defined Benefit Plan, Benefit Obligation, Benefits Paid	3,136	9,481
Foreign currency exchange rate changes	13,014	(4,386)
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Curtailment	(858)	14
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement	(175)	(1,431)
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Other Change	833	0
Benefit obligation at December 31,	110,820	97,261	98,767
Fair value of plan assets at January 1,	10,215	9,662
Actual return on plan assets	786	604
Company contributions	399	348
Defined Benefit Plan, Plan Assets, Benefits Paid	383	370
Foreign currency exchange rate changes	984	(29)
Defined Benefit Plan, Plan Assets, Period Increase (Decrease)	833	0
Fair value of plan assets at December 31,	12,834	10,215	$ 9,662
Net pension benefit obligation at fair value	$ 97,986	$ 87,046