Defined Severance Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Retirement Benefits [Abstract]
Current service costs	$ 32,224	$ 14,758	$ 62,779	$ 29,179
Interest expense	591	316	1,185	640
Amortization of:
Prior service credit	23	0	46	0
Net actuarial loss	918	36	2,018	73
Net periodic benefit costs charged to expense	$ 33,756	$ 15,110	$ 66,028	$ 29,892