Pension and Severance Plans (Defined Benefit Plans - Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan [Abstract]
Prepaid benefit cost (included in non-current assets)	$ 498	$ 2,740
Accrued benefit liability (included in pension and severance obligations)	(62,788)	(55,082)
Net amount recognized at year end	$ (62,290)	$ (52,342)

Amount of asset, recognized in statement of financial position, for overfunded defined benefit pension and other postretirement plans.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant