Retirement Plans and Postretirement Medical Benefits (Pension Plans with an Accumulated Benefit Obligation in Excess of Plan Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
United States
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 1,729,638	$ 1,612,745
Accumulated benefit obligation	1,729,194	1,612,241
Fair value of plan assets	1,601,000	1,486,325
Foreign
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	691,909	615,288
Accumulated benefit obligation	690,887	614,293
Fair value of plan assets	$ 577,821	$ 516,634

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Amount of accumulated benefit obligation for defined benefit plan with accumulated benefit obligation in excess of plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
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Amount of plan asset for defined benefit plan with accumulated benefit obligation in excess of plan assets.

+ References

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-Publisher FASB
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Amount of projected benefit obligation for defined benefit pension plan with accumulated benefit obligation in excess of plan assets.

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