Pension and Other Postretirement Benefits - Funded Status Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets at Beginning of Year	$ 136,041
Fair Value of Plan Assets at End of Year		$ 136,041
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Non-current Asset	1,184	0
Domestic [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets at Beginning of Year	49,197
Fair Value of Plan Assets at End of Year		49,197
Domestic [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation at Beginning of Year	67,254	66,862
Service Cost	337	298	$ 250
Interest Cost	1,932	2,114	2,541
Employee Contributions	0	0
Benefits Paid	(4,031)	(4,522)
Plan Settlements	(4,341)	0
Plan Expense and Premiums Paid	0	(275)
Actuarial (gain) Loss	1,826	2,777
Translation Difference and Other	0	0
Benefit Obligation at End of Year	62,977	67,254	66,862
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets at Beginning of Year	49,197	46,701
Actual Return on Plan Assets	6,865	2,516
Employer Contributions	4,574	4,777
Employee Contributions	0	0
Benefits Paid	(4,031)	(4,522)
Plan Settlements	(4,341)	0
Plan Expenses and Premiums Paid	(300)	(275)
Translation Difference	0	0
Fair Value of Plan Assets at End of Year	51,964	49,197	46,701
Defined Benefit Plan, Funded Status of Plan	(11,013)	(18,057)
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Non-current Asset	1,184	0
Current Liabilities	(560)	(574)
Non-current Liabilities	(11,637)	(17,483)
Net Amount Recognized	(11,013)	(18,057)
Amounts Not Yet Reflected in Net Periodic Benefit Costs and Included in Accumulated Other Comprehensive Income (Loss) [Abstract]
Prior Service credit (cost)	(59)	(122)
Accumulated Loss	(27,133)	(33,147)
Accumulated Other Comprehensive Loss ("AOCI")	(27,192)	(33,269)
Cumulative Employer Contributions In Excess Of (or Below) Net Periodic Benefit Cost	16,179	15,212
Net Amount Recognized	(11,013)	(18,057)
Domestic [Member] | Other Postretirement Benefit Plans Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation at Beginning of Year	4,730	5,422
Service Cost	8	10	17
Interest Cost	144	142	195
Employee Contributions	0	0
Benefits Paid	(448)	(443)
Plan Settlements	0	0
Plan Expense and Premiums Paid	0	0
Actuarial (gain) Loss	295	(401)
Translation Difference and Other	0	0
Benefit Obligation at End of Year	4,729	4,730	5,422
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets at Beginning of Year	0	0
Actual Return on Plan Assets	0	0
Employer Contributions	448	443
Employee Contributions	0	0
Benefits Paid	(448)	(443)
Plan Settlements	0	0
Plan Expenses and Premiums Paid	0	0
Translation Difference	0	0
Fair Value of Plan Assets at End of Year	0	0	0
Defined Benefit Plan, Funded Status of Plan	(4,729)	(4,730)
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Non-current Asset	0	0
Current Liabilities	(459)	(451)
Non-current Liabilities	(4,270)	(4,279)
Net Amount Recognized	(4,729)	(4,730)
Amounts Not Yet Reflected in Net Periodic Benefit Costs and Included in Accumulated Other Comprehensive Income (Loss) [Abstract]
Prior Service credit (cost)	0	0
Accumulated Loss	(823)	(581)
Accumulated Other Comprehensive Loss ("AOCI")	(823)	(581)
Cumulative Employer Contributions In Excess Of (or Below) Net Periodic Benefit Cost	(3,906)	(4,149)
Net Amount Recognized	(4,729)	(4,730)
Foreign [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets at Beginning of Year	86,844
Fair Value of Plan Assets at End of Year		86,844
Foreign [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation at Beginning of Year	103,491	92,406
Service Cost	3,219	2,378	2,799
Interest Cost	2,066	2,314	2,476
Employee Contributions	68	71
Benefits Paid	(2,503)	(1,583)
Plan Settlements	0	0
Plan Expense and Premiums Paid	(210)	(155)
Actuarial (gain) Loss	(1,164)	14,848
Translation Difference and Other	13,385	(6,788)
Benefit Obligation at End of Year	118,352	103,491	92,406
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets at Beginning of Year	86,844	76,156
Actual Return on Plan Assets	116	14,472
Employer Contributions	2,867	3,103
Employee Contributions	68	71
Benefits Paid	(2,503)	(1,583)
Plan Settlements	0	0
Plan Expenses and Premiums Paid	(210)	(155)
Translation Difference	11,440	(5,220)
Fair Value of Plan Assets at End of Year	98,622	86,844	76,156
Defined Benefit Plan, Funded Status of Plan	(19,730)	(16,647)
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Non-current Asset	0	0
Current Liabilities	(89)	(61)
Non-current Liabilities	(19,641)	(16,586)
Net Amount Recognized	(19,730)	(16,647)
Amounts Not Yet Reflected in Net Periodic Benefit Costs and Included in Accumulated Other Comprehensive Income (Loss) [Abstract]
Prior Service credit (cost)	1,744	1,687
Accumulated Loss	(22,598)	(20,214)
Accumulated Other Comprehensive Loss ("AOCI")	(20,854)	(18,527)
Cumulative Employer Contributions In Excess Of (or Below) Net Periodic Benefit Cost	1,124	1,880
Net Amount Recognized	(19,730)	(16,647)
Pension Plans, Defined Benefit [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation at Beginning of Year	170,745	159,268
Service Cost	3,556	2,676	3,049
Interest Cost	3,998	4,428	5,017
Employee Contributions	68	71
Benefits Paid	(6,534)	(6,105)
Plan Settlements	(4,341)	0
Plan Expense and Premiums Paid	(210)	(430)
Actuarial (gain) Loss	662	17,625
Translation Difference and Other	13,385	(6,788)
Benefit Obligation at End of Year	181,329	170,745	159,268
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets at Beginning of Year	136,041	122,857
Actual Return on Plan Assets	6,981	16,988
Employer Contributions	7,441	7,880
Employee Contributions	68	71
Benefits Paid	(6,534)	(6,105)
Plan Settlements	4,341	0
Plan Expenses and Premiums Paid	(510)	(430)
Translation Difference	11,440	(5,220)
Fair Value of Plan Assets at End of Year	150,586	136,041	$ 122,857
Defined Benefit Plan, Funded Status of Plan	(30,743)	(34,704)
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Non-current Asset	1,184	0
Current Liabilities	(649)	(635)
Non-current Liabilities	(31,278)	(34,069)
Net Amount Recognized	(30,743)	(34,704)
Amounts Not Yet Reflected in Net Periodic Benefit Costs and Included in Accumulated Other Comprehensive Income (Loss) [Abstract]
Prior Service credit (cost)	1,685	1,565
Accumulated Loss	(49,731)	(53,361)
Accumulated Other Comprehensive Loss ("AOCI")	(48,046)	(51,796)
Cumulative Employer Contributions In Excess Of (or Below) Net Periodic Benefit Cost	17,303	17,092
Net Amount Recognized	$ (30,743)	$ (34,704)