Employee Benefits (Details) - Information Related to Changes in Projected Benefit Obligation - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of year	$ 38,400	$ 35,870	$ 38,115
Service cost	2,820	2,780	2,620
Interest cost	765	850	790
Actuarial loss (gain) due to assumption changes and plan experience	690	1,480	(1,190)
Additions and contractual termination benefits	(860)	0	85
Benefits paid	(920)	(1,640)	(775)
Foreign currency impact	4,555	(940)	(3,775)
Projected benefit obligation at end of year	$ 45,450	$ 38,400	$ 35,870