Retirement Plans and Postretirement Medical Benefits (Other Changes in Plan Assets and Benefit Obligations) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Nonpension postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	$ 5,134	$ (13,934)
Amortization of net actuarial loss	(3,600)	(3,615)
Amortization of prior service credit	(297)	(297)
Total recognized in other comprehensive income	1,237	(17,846)
United States
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	(9,304)	22,728
Amortization of net actuarial loss	(28,954)	(27,220)
Amortization of prior service credit	60	60
Net transition asset	0	0
Settlement	0	(2,109)
Total recognized in other comprehensive income	(38,198)	(6,541)
Foreign
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	(12,202)	91,549
Amortization of net actuarial loss	(8,052)	(5,264)
Amortization of prior service credit	71	73
Net transition asset	8	8
Settlement	0	(110)
Total recognized in other comprehensive income	$ (20,175)	$ 86,256