Retirement Plans - Net Pension Income Domestic and Foreign (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension Plans
Net pension expense (income)
(Income) expense, net	$ (492)	$ (440)	$ (1,416)	$ (1,234)
United States Pension Plan of US Entity [Member]
Net pension expense (income)
Service cost	0	21	0	65
Interest cost	2,068	2,756	6,204	8,268
Defined Benefit Plan, Expected Return on Plan Assets, Net of Expenses	(4,060)	(4,744)	(12,181)	(14,232)
Amortization of loss	1,446	1,499	4,338	4,495
Other cost due to retirement			61	12
(Income) expense, net	(546)	(468)	(1,578)	(1,392)
Foreign Pension Plans
Net pension expense (income)
Service cost	12	13	36	38
Interest cost	8	12	25	34
Defined Benefit Plan, Expected Return on Plan Assets, Net of Expenses	(5)	(33)	(15)	(19)
Amortization of loss	39	36	116	105
Other cost due to retirement			0	0
(Income) expense, net	$ 54	$ 28	$ 162	$ 158