Pension and Severance Plans (Changes and Components) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Service cost	$ 29,848	$ 31,355	$ 32,913
Interest cost	4,980	5,244	4,867
Expected return on plan assets	(5,506)	(6,412)	(5,640)
Amortization of prior service cost	0	0	6
Recognized actuarial (gain) loss	56	(374)	(147)
Net periodic pension cost	29,378	29,813	31,999
Settlement (gain) loss	62	(210)	(1,639)
Total pension expense	$ 29,440	$ 29,603	$ 30,360