Pension and Postretirement Benefits (Plan Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Postretirement Medical Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Company contributions	$ 2,500	$ 4,400	$ 5,100
Domestic Plan
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	418,854	408,218
Return on plan assets	59,462	28,182
Company contributions	23,836	22,450
Benefits paid	(33,779)	(37,787)
Settlements	(3,594)	(2,209)
Ending balance	464,779	418,854	408,218
Fair value of plan assets	418,854	408,218	408,218
Domestic Plan | Hierarchial Level 1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	848
Ending balance	5,494	848
Fair value of plan assets	848	848
Domestic Plan | Hierarchial Level 2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	418,006
Ending balance	459,285	418,006
Fair value of plan assets	418,006	418,006
Domestic Plan | Hierarchial Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Domestic Plan | Cash
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	848
Ending balance	5,494	848
Fair value of plan assets	848	848
Domestic Plan | Cash | Hierarchial Level 1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	848
Ending balance	5,494	848
Fair value of plan assets	848	848
Domestic Plan | Cash | Hierarchial Level 2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Domestic Plan | Cash | Hierarchial Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Domestic Plan | U.S. Large Cap
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	81,953
Ending balance	0	81,953
Fair value of plan assets	81,953	81,953
Domestic Plan | U.S. Large Cap | Hierarchial Level 1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Domestic Plan | U.S. Large Cap | Hierarchial Level 2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	81,953
Ending balance	0	81,953
Fair value of plan assets	81,953	81,953
Domestic Plan | U.S. Large Cap | Hierarchial Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Domestic Plan | U.S. Small Cap
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	17,738
Ending balance	0	17,738
Fair value of plan assets	17,738	17,738
Domestic Plan | U.S. Small Cap | Hierarchial Level 1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Domestic Plan | U.S. Small Cap | Hierarchial Level 2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	17,738
Ending balance	0	17,738
Fair value of plan assets	17,738	17,738
Domestic Plan | U.S. Small Cap | Hierarchial Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Domestic Plan | International Large Cap
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	59,435
Ending balance	0	59,435
Fair value of plan assets	59,435	59,435
Domestic Plan | International Large Cap | Hierarchial Level 1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Domestic Plan | International Large Cap | Hierarchial Level 2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	59,435
Ending balance	0	59,435
Fair value of plan assets	59,435	59,435
Domestic Plan | International Large Cap | Hierarchial Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Domestic Plan | Emerging Markets
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	20,014
Ending balance	0	20,014
Fair value of plan assets	20,014	20,014
Domestic Plan | Emerging Markets | Hierarchial Level 1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Domestic Plan | Emerging Markets | Hierarchial Level 2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	20,014
Ending balance	0	20,014
Fair value of plan assets	20,014	20,014
Domestic Plan | Emerging Markets | Hierarchial Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Domestic Plan | World Equity
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	34,261
Ending balance	0	34,261
Fair value of plan assets	34,261	34,261
Domestic Plan | World Equity | Hierarchial Level 1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Domestic Plan | World Equity | Hierarchial Level 2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	34,261
Ending balance	0	34,261
Fair value of plan assets	34,261	34,261
Domestic Plan | World Equity | Hierarchial Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Domestic Plan | Global Equity
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	167,336	0
Fair value of plan assets	0	0
Domestic Plan | Global Equity | Hierarchial Level 1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Domestic Plan | Global Equity | Hierarchial Level 2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	167,336	0
Fair value of plan assets	0	0
Domestic Plan | Global Equity | Hierarchial Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Domestic Plan | Global Real Assets
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	55,261	0
Fair value of plan assets	0	0
Domestic Plan | Global Real Assets | Hierarchial Level 1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Domestic Plan | Global Real Assets | Hierarchial Level 2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	55,261	0
Fair value of plan assets	0	0
Domestic Plan | Global Real Assets | Hierarchial Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Domestic Plan | Diversified Credit
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	55,440	0
Fair value of plan assets	0	0
Domestic Plan | Diversified Credit | Hierarchial Level 1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Domestic Plan | Diversified Credit | Hierarchial Level 2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	55,440	0
Fair value of plan assets	0	0
Domestic Plan | Diversified Credit | Hierarchial Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Domestic Plan | Liability Driven Investment
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	164,384
Ending balance	181,248	164,384
Fair value of plan assets	164,384	164,384
Domestic Plan | Liability Driven Investment | Hierarchial Level 1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Domestic Plan | Liability Driven Investment | Hierarchial Level 2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	164,384
Ending balance	181,248	164,384
Fair value of plan assets	164,384	164,384
Domestic Plan | Liability Driven Investment | Hierarchial Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Domestic Plan | Long-Term Government/Credit
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	40,221
Ending balance	0	40,221
Fair value of plan assets	40,221	40,221
Domestic Plan | Long-Term Government/Credit | Hierarchial Level 1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Domestic Plan | Long-Term Government/Credit | Hierarchial Level 2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	40,221
Ending balance	0	40,221
Fair value of plan assets	40,221	40,221
Domestic Plan | Long-Term Government/Credit | Hierarchial Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Foreign Plan
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	223,491	230,827
Return on plan assets	10,871	33,073
Employee contributions	228	219
Company contributions	18,494	20,004
Settlements	(7,383)	(4,511)
Currency translation impact and other	21,733	(34,386)
Benefits paid	(18,701)	(21,735)
Ending balance	248,733	223,491	230,827
Fair value of plan assets	223,491	230,827	$ 230,827
Foreign Plan | Hierarchial Level 1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	10,396
Ending balance	6,815	10,396
Fair value of plan assets	10,396	10,396
Foreign Plan | Hierarchial Level 2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	179,218
Ending balance	203,306	179,218
Fair value of plan assets	179,218	179,218
Foreign Plan | Hierarchial Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	33,877
Ending balance	38,612	33,877
Fair value of plan assets	33,877	33,877
Foreign Plan | Cash
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	10,396
Ending balance	6,815	10,396
Fair value of plan assets	10,396	10,396
Foreign Plan | Cash | Hierarchial Level 1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	10,396
Ending balance	6,815	10,396
Fair value of plan assets	10,396	10,396
Foreign Plan | Cash | Hierarchial Level 2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Foreign Plan | Cash | Hierarchial Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Foreign Plan | North American Companies
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	5,945
Ending balance	7,119	5,945
Fair value of plan assets	5,945	5,945
Foreign Plan | North American Companies | Hierarchial Level 1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Foreign Plan | North American Companies | Hierarchial Level 2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	5,945
Ending balance	7,119	5,945
Fair value of plan assets	5,945	5,945
Foreign Plan | North American Companies | Hierarchial Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Foreign Plan | Global Equity
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	16,774
Ending balance	8,951	16,774
Fair value of plan assets	16,774	16,774
Foreign Plan | Global Equity | Hierarchial Level 1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Foreign Plan | Global Equity | Hierarchial Level 2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	16,774
Ending balance	8,951	16,774
Fair value of plan assets	16,774	16,774
Foreign Plan | Global Equity | Hierarchial Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Foreign Plan | U.K. Government Gilt Index
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	68,227
Ending balance	103,230	68,227
Fair value of plan assets	68,227	68,227
Foreign Plan | U.K. Government Gilt Index | Hierarchial Level 1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Foreign Plan | U.K. Government Gilt Index | Hierarchial Level 2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	68,227
Ending balance	103,230	68,227
Fair value of plan assets	68,227	68,227
Foreign Plan | U.K. Government Gilt Index | Hierarchial Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Foreign Plan | U.K. Corporate Bond Index
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	2,785
Ending balance	1,316	2,785
Fair value of plan assets	2,785	2,785
Foreign Plan | U.K. Corporate Bond Index | Hierarchial Level 1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Foreign Plan | U.K. Corporate Bond Index | Hierarchial Level 2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	2,785
Ending balance	1,316	2,785
Fair value of plan assets	2,785	2,785
Foreign Plan | U.K. Corporate Bond Index | Hierarchial Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Foreign Plan | Global Index Income Bond
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	5,259
Ending balance	5,350	5,259
Fair value of plan assets	5,259	5,259
Foreign Plan | Global Index Income Bond | Hierarchial Level 1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Foreign Plan | Global Index Income Bond | Hierarchial Level 2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	5,259
Ending balance	5,350	5,259
Fair value of plan assets	5,259	5,259
Foreign Plan | Global Index Income Bond | Hierarchial Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Foreign Plan | Liability Driven Investment [Member] [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	25,348
Ending balance	21,837	25,348
Fair value of plan assets	25,348	25,348
Foreign Plan | Liability Driven Investment [Member] [Member] | Hierarchial Level 1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Foreign Plan | Liability Driven Investment [Member] [Member] | Hierarchial Level 2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	25,348
Ending balance	21,837	25,348
Fair value of plan assets	25,348	25,348
Foreign Plan | Liability Driven Investment [Member] [Member] | Hierarchial Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Foreign Plan | Multi-Asset Category
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	54,880
Ending balance	55,503	54,880
Fair value of plan assets	54,880	54,880
Foreign Plan | Multi-Asset Category | Hierarchial Level 1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Foreign Plan | Multi-Asset Category | Hierarchial Level 2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	54,880
Ending balance	55,503	54,880
Fair value of plan assets	54,880	54,880
Foreign Plan | Multi-Asset Category | Hierarchial Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Foreign Plan | Buy-in Contract
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	20,931
Ending balance	24,484	20,931
Fair value of plan assets	20,931	20,931
Foreign Plan | Buy-in Contract | Hierarchial Level 1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Foreign Plan | Buy-in Contract | Hierarchial Level 2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Foreign Plan | Buy-in Contract | Hierarchial Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Ending balance	24,484
Fair value of plan assets	24,484
Foreign Plan | Other Types
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	12,946
Ending balance	14,128	12,946
Fair value of plan assets	12,946	12,946
Foreign Plan | Other Types | Hierarchial Level 1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Foreign Plan | Other Types | Hierarchial Level 2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	0
Ending balance	0	0
Fair value of plan assets	0	0
Foreign Plan | Other Types | Hierarchial Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning balance	12,946
Ending balance	14,128	12,946
Fair value of plan assets	$ 12,946	$ 12,946