Pension and Postretirement Benefits (Change in Benefit Obligation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Postretirement Medical Benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Balance —	$ 27,317	$ 28,614
Service cost	0	1	$ 2
Interest cost	919	1,154	1,155
Employee contributions	939	856
Medicare subsidies receivable	235	117
Actuarial loss (gain)	(1,818)	1,907
Benefits paid	(3,710)	(5,332)
Balance —	23,882	27,317	28,614
Domestic Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Balance —	449,601	426,248
Service cost	22,257	22,583	24,113
Interest cost	16,878	19,072	17,072
Other	(3,006)	(3,221)
Actuarial loss (gain)	9,404	22,706
Benefits paid	(33,779)	(37,787)
Balance —	461,355	449,601	426,248
Accumulated benefit obligations	461,355	449,601
Foreign Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Balance —	383,947	386,175
Service cost	7,247	7,131	7,832
Interest cost	9,320	11,623	11,770
Employee contributions	228	219
Settlements and other	(9,260)	(10,347)
Actuarial loss (gain)	(1,913)	49,826
Benefits paid	(18,701)	(21,735)
Currency translation impact	43,092	(38,945)
Balance —	413,960	383,947	$ 386,175
Accumulated benefit obligations	$ 391,102	$ 362,618