Employee and Retiree Benefit Plans - Plans' Benefit Obligations and Fair Value of Assets and Statement of Funded Status (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in plan assets
Beginning balance	$ 547,484
Ending balance	586,720	$ 547,484
Pension Benefits
Change in benefit obligation
Beginning balance	883,269	777,645
Service cost	7,967	7,964	$ 8,994
Interest cost	21,127	27,835	26,168
Participant contributions	0	11
Actuarial loss (gain)	107,258	103,374
Medicare Part D subsidy	0	0
Exchange rate changes	7,074	7,687
Benefits paid	(46,066)	(41,247)
Curtailments	(7,596)	0
Special termination benefits	8,434	0
Ending balance	981,467	883,269	777,645
Change in plan assets
Beginning balance	547,484	487,094
Actual return on plan assets	48,115	70,893
Employer contributions	30,178	25,915
Participant contributions	0	11
Medicare Part D subsidy	0	0
Exchange rate changes	7,009	7,328
Benefits paid	(46,066)	(41,247)
Other	0	(2,510)
Ending balance	586,720	547,484	487,094
Funded status and amounts recognized in the Consolidated Balance Sheets at December 31
Deferred charges and other assets	4,572	5,353
Other accrued liabilities	(9,468)	(8,810)
Deferred credits and other liabilities	(389,851)	(332,328)
Funded status and net plan liability recognized at December 31	(394,747)	(335,785)
Other Postretirement Benefits
Change in benefit obligation
Beginning balance	108,401	94,779
Service cost	1,373	1,559	1,965
Interest cost	2,626	3,864	3,427
Participant contributions	2,225	1,930
Actuarial loss (gain)	3,758	10,503
Medicare Part D subsidy	243	234
Exchange rate changes	13	30
Benefits paid	(4,238)	(4,498)
Curtailments	(6,023)	0
Special termination benefits	0	0
Ending balance	108,378	108,401	94,779
Change in plan assets
Beginning balance	0	0
Actual return on plan assets	0	0
Employer contributions	1,770	2,333
Participant contributions	2,225	1,930
Medicare Part D subsidy	243	234
Exchange rate changes	0	0
Benefits paid	(4,238)	(4,497)
Other	0	0
Ending balance	0	0	$ 0
Funded status and amounts recognized in the Consolidated Balance Sheets at December 31
Deferred charges and other assets	0	0
Other accrued liabilities	(5,298)	(5,234)
Deferred credits and other liabilities	(103,080)	(103,167)
Funded status and net plan liability recognized at December 31	$ (108,378)	$ (108,401)