Retirement Plans - Estimated Future Benefit Payments (Details 14) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 286,539	$ 293,567
Post-Retirement Life Insurance Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0	$ 0
Estimated Future Benefit Payments
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	418
2017	405
2018	392
2019	378
2020	363
2023-2026	1,610
Total	3,566
Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	284,762	292,044	289,315
Estimated Future Benefit Payments
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	15,693
2017	15,705
2018	15,673
2019	15,548
2020	15,361
2023-2026	72,669
Total	150,649
Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	1,777	$ 1,523	$ 1,480
Estimated Future Benefit Payments
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	67
2017	72
2018	242
2019	63
2020	69
2023-2026	532
Total	$ 1,045