Pension and Severance Plans (Changes and Components) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan [Abstract]
Service cost	$ 31,355	$ 32,913	$ 33,823
Interest cost	5,244	4,867	4,067
Expected return on plan assets	(6,412)	(5,640)	(4,537)
Amortization of prior service cost	0	6	30
Recognized actuarial (gain) loss	(374)	(147)	84
Net periodic pension cost	29,813	31,999	33,467
Curtailment loss	0	0	574
Settlement (gain) loss	(210)	(1,639)	383
Total pension expense	$ 29,603	$ 30,360	$ 34,424