Pension and Other Postretirement Benefits - Change in Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Change in plan assets:
Fair value of plan assets, beginning of year	$ 355,726
Fair value of plan assets, end of year	361,802	$ 355,726
Pension Benefits
Change in plan assets:
Fair value of plan assets, beginning of year	355,726	311,509
Actual return on plan assets	32,470	45,896
Employer contributions	6,393	5,673
Plan participant contributions	73	86
Settlements	(26,945)	0
Foreign currency exchange rate changes	7,803	9,275
Benefits paid	(13,718)	(16,713)
Fair value of plan assets, end of year	361,802	355,726
Other Benefits
Change in plan assets:
Fair value of plan assets, beginning of year	0	0
Actual return on plan assets	0	0
Employer contributions	1,351	1,302
Plan participant contributions	5	4
Settlements	0	0
Foreign currency exchange rate changes	0	0
Benefits paid	(1,356)	(1,306)
Fair value of plan assets, end of year	$ 0	$ 0