Retirement Plans - Net Pension Income Domestic and Foreign (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pension Plans
Net pension expense (income)
(Income) expense, net	$ 79	$ (433)
Foreign Plan [Member]
Net pension expense (income)
Service cost	11	12
Interest cost	11	8
Defined Benefit Plan, Expected Return on Plan Assets, Net of Expenses	(7)	(5)
Amortization of loss	42	38
(Income) expense, net	57	53
Domestic Plan [Member]
Net pension expense (income)
Interest cost	1,781	2,068
Defined Benefit Plan, Expected Return on Plan Assets, Net of Expenses	(3,225)	(4,061)
Amortization of loss	1,466	1,446
Other cost due to retirement	0	61
(Income) expense, net	$ 22	$ (486)