Postretirement Benefit Plans (Changes in the pension benefit obligation and plan assets) (Details) - Korea Defined Benefit Plan - USD ($) $ in Thousands	8 Months Ended		12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2018
Change in benefit obligation:
Beginning benefit obligation	$ 3,360		$ 3,966
Service cost	361	$ 590	590
Interest cost	55	110	110
Benefits paid	(212)		(503)
Actuarial loss	174		518
Effect of foreign currency translation	228		(172)
Projected benefit obligation at end of year	3,966	3,966	4,509
Fair value of plan assets	24	24	20
Funded status at end of year	$ 3,942	$ 3,942	$ 4,489