Pension and Severance Plans (Changes and Components) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan [Abstract]
Service cost	$ 32,913	$ 33,823	$ 33,854
Interest cost	4,867	4,067	3,641
Expected return on plan assets	(5,640)	(4,537)	(3,788)
Amortization of prior service cost	6	30	35
Recognized actuarial (gain) loss	(147)	84	94
Net periodic pension cost	31,999	33,467	33,836
Curtailment loss	0	574	0
Settlement (gain) loss	(1,639)	383	128
Total pension expense	$ 30,360	$ 34,424	$ 33,964