Retirement Plans and Postretirement Medical Benefits (Components of Net Periodic Benefit Cost for Defined Benefit Pension Plans) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Nonpension postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 885	$ 967	$ 1,405
Interest cost	4,993	6,584	6,640
Amortization of prior service (credit) cost	373	321	304
Amortization of net actuarial loss	3,198	2,026	3,048
Curtailment	0	0	246
Net periodic benefit cost (income)	9,449	9,898	11,643
United States | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	86	83	92
Interest cost	52,103	63,171	61,490
Expected return on plan assets	(84,719)	(92,726)	(101,087)
Amortization of net transition asset	0	0	0
Amortization of prior service (credit) cost	(60)	(60)	(60)
Amortization of net actuarial loss	32,490	26,146	31,298
Special termination benefits	0	0	0
Settlements and curtailments	1,364	2,381	44,665
Net periodic benefit cost (income)	1,264	(1,005)	36,398
Foreign | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	1,650	1,543	2,159
Interest cost	13,379	17,853	18,089
Expected return on plan assets	(34,391)	(34,363)	(35,687)
Amortization of net transition asset	(4)	(6)	(7)
Amortization of prior service (credit) cost	245	243	(71)
Amortization of net actuarial loss	7,842	6,337	7,264
Special termination benefits	0	0	208
Settlements and curtailments	5,060	397	(13)
Net periodic benefit cost (income)	$ (6,219)	$ (7,996)	$ (8,058)