Retirement Plans and Postretirement Medical Benefits (Level 3 Gains and Losses) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
United States
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at	$ 129,714	$ 138,725
Realized gains	9,265	10,231
Unrealized gains (losses)	3,053	112
Net purchases, sales and settlements	(12,405)	(19,354)
Balance at	129,627	129,714
United States | Mortgage-backed securities /asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at	0	1,236
Realized gains	0	25
Unrealized gains (losses)	0	49
Net purchases, sales and settlements	0	(1,310)
Balance at	0	0
United States | Private equity
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at	38,362	49,637
Realized gains	8,264	9,226
Unrealized gains (losses)	(1,409)	(2,334)
Net purchases, sales and settlements	(12,467)	(18,167)
Balance at	32,750	38,362
United States | Real estate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at	91,352	87,852
Realized gains	1,001	980
Unrealized gains (losses)	4,462	2,397
Net purchases, sales and settlements	62	123
Balance at	96,877	91,352
Foreign
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at	85,625	71,262
Unrealized gains (losses)	(3,631)	5,710
Net purchases, sales and settlements	5,743	1,481
Foreign currency	(4,828)	7,172
Balance at	82,909	85,625
Foreign | Real estate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at	41,601	34,483
Unrealized gains (losses)	1,317	2,159
Net purchases, sales and settlements	1,653	1,481
Foreign currency	(2,428)	3,478
Balance at	42,143	41,601
Foreign | Diversified growth funds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at	44,024	36,779
Unrealized gains (losses)	(4,948)	3,551
Net purchases, sales and settlements	4,090	0
Foreign currency	(2,400)	3,694
Balance at	$ 40,766	$ 44,024