Postretirement Benefit Plans (Net periodic pension cost (income) and other amounts recognized in other comprehensive income (loss) before taxes) (Details) - Korea Defined Benefit Plan - USD ($) $ in Thousands	8 Months Ended			12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2018
Components of net periodic defined benefit plan cost:
Service cost		$ 361	$ 590	$ 590
Interest cost		55	110	110
Net periodic defined benefit plan cost		416	700
Other amounts recognized in other comprehensive income (loss) before income taxes are as follows:
Actuarial loss before taxes	$ 174	(174)	(518)	$ 692
Total (income) loss recognized in other comprehensive income, before taxes		174	518
Total (income) recognized in net periodic pension cost and other comprehensive income, before taxes		$ 590	$ 1,218