Retirement Plans and Postretirement Medical Benefits (Pension Plans with an Accumulated Benefit Obligation in Excess of Plan Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 426,000	$ 477,000
United States
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	1,500,680	1,727,292
Accumulated benefit obligation	1,500,231	1,726,378
Fair value of plan assets	1,326,296	1,557,069
Foreign
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	540,798	614,371
Accumulated benefit obligation	538,666	601,412
Fair value of plan assets	$ 426,446	$ 476,825