Pension and Other Postretirement Benefits - Net Periodic Benefit Cost and Changes in Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Domestic [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service Cost	$ 337	$ 298	$ 250
Interest Cost	1,932	2,114	2,541
Expected Return on Plan Assets	(3,067)	(3,316)	(3,453)
Settlement Loss	1,946	0	0
Actuarial Loss Amortization	2,396	2,336	2,353
Prior Service (Credit) Cost Amortization	63	63	63
Net Periodic Benefit Cost	3,607	1,495	1,754
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Net Loss (Gain) Arising During The Period	(1,672)	3,576	1,134
Prior Service (Credit) Cost Amortization	(63)	(63)	(63)
Actuarial Loss	(4,342)	(2,336)	(2,353)
Foreign Currency Exchange Rate Changes	0	0	0
Total Recognized in Other Comprehensive (Income) Loss	(6,077)	1,177	(1,282)
Total Recognized In Net Periodic Benefit Cost And Other Comprehensive Loss Or (Income)	(2,470)	2,672	472
Domestic [Member] | Other Postretirement Benefit Plans Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service Cost	8	10	17
Interest Cost	144	142	195
Actuarial Loss Amortization	54	0	83
Net Periodic Benefit Cost	206	152	295
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Net Loss (Gain) Arising During The Period	295	(401)	(302)
Actuarial Loss	(54)	0	(83)
Total Recognized in Other Comprehensive (Income) Loss	241	(401)	(385)
Total Recognized In Net Periodic Benefit Cost And Other Comprehensive Loss Or (Income)	447	(249)	(90)
Foreign [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service Cost	3,219	2,378	2,799
Interest Cost	2,066	2,314	2,476
Expected Return on Plan Assets	(1,994)	(2,026)	(2,092)
Settlement Loss	0	0	170
Actuarial Loss Amortization	862	839	1,136
Prior Service (Credit) Cost Amortization	(167)	(164)	(164)
Net Periodic Benefit Cost	3,986	3,341	4,325
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Net Loss (Gain) Arising During The Period	715	2,401	(3,537)
Prior Service (Credit) Cost Amortization	167	164	164
Actuarial Loss	(862)	(839)	(1,306)
Foreign Currency Exchange Rate Changes	2,308	(1,347)	(2,353)
Total Recognized in Other Comprehensive (Income) Loss	2,328	379	(7,032)
Total Recognized In Net Periodic Benefit Cost And Other Comprehensive Loss Or (Income)	6,314	3,720	(2,707)
Pension Plans, Defined Benefit [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service Cost	3,556	2,676	3,049
Interest Cost	3,998	4,428	5,017
Expected Return on Plan Assets	(5,061)	(5,342)	(5,545)
Settlement Loss	1,946	0	170
Actuarial Loss Amortization	3,258	3,175	3,489
Prior Service (Credit) Cost Amortization	(104)	(101)	(101)
Net Periodic Benefit Cost	7,593	4,836	6,079
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Net Loss (Gain) Arising During The Period	(957)	5,977	(2,403)
Prior Service (Credit) Cost Amortization	104	101	101
Actuarial Loss	(5,204)	(3,175)	(3,659)
Foreign Currency Exchange Rate Changes	2,308	(1,347)	(2,353)
Total Recognized in Other Comprehensive (Income) Loss	(3,749)	1,556	(8,314)
Total Recognized In Net Periodic Benefit Cost And Other Comprehensive Loss Or (Income)	$ 3,844	$ 6,392	$ (2,235)