Retirement Plans - Net Pension Income or Postretirement Expense (Details 6) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Post-Retirement Life Insurance Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	$ 418
Net pension expense (income)
Service cost	2	$ 3	$ 5
Interest cost	161	207	204
Defined Benefit Plan, Amortization of Gain (Loss)	101	149	101
Net expense (income)	$ 62	$ 61	$ 108
Benefit obligation assumptions:
Discount rate	3.59%	4.10%	4.43%
Rate of compensation increase	0.00%	0.00%	0.00%
Pension income/expense assumptions:
Discount rate	4.10%	4.43%	4.07%
Rate of compensation increase	0.00%	0.00%	0.00%
Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	$ 67
Net pension expense (income)
Service cost	48	$ 51	$ 63
Interest cost	34	46	465
Expected return on plan assets	(20)	(26)	(446)
Defined Benefit Plan, Amortization of Gain (Loss)	(155)	(140)	(7,492)
Additional cost due to early retirement	0	0	651
Settlement loss	0	0	0
Net expense (income)	$ 217	$ 211	$ 8,225
Benefit obligation assumptions:
Discount rate	1.38%	1.13%	1.63%
Rate of compensation increase	2.00%	2.00%	2.00%
Pension income/expense assumptions:
Discount rate	1.13%	1.63%	3.13%
Expected return on plan assets	1.13%	1.63%	2.00%
Rate of compensation increase	2.00%	2.00%	0.48%
Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	$ 15,693
Net pension expense (income)
Service cost	0	$ 87	$ 171
Interest cost	8,273	11,024	11,258
Expected return on plan assets	(16,243)	(18,976)	(20,272)
Defined Benefit Plan, Amortization of Gain (Loss)	(5,785)	(5,994)	(6,339)
Additional cost due to early retirement	0	0	0
Settlement loss	13,476	0	0
Net expense (income)	$ 11,291	$ (1,871)	$ (2,504)
Benefit obligation assumptions:
Discount rate	3.63%	4.16%	4.43%
Rate of compensation increase	0.00%	0.00%	0.00%
Pension income/expense assumptions:
Discount rate	4.16%	4.43%	4.07%
Expected return on plan assets	5.61%	6.63%	7.00%
Rate of compensation increase	0.00%	0.00%	0.00%