Retirement Plans - Other Postretirement Benefit Plan (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure
Service cost	$ 0	$ 0	$ 1	$ 2
Interest cost	41	52	121	156
Amortization of gain	(25)	(37)	(75)	(112)
(Income) expense, net	16	15	47	46
Foreign Pension Plans
Defined Benefit Plan Disclosure
Service cost	12	13	36	38
Interest cost	8	12	25	34
Amortization of gain	39	36	116	105
(Income) expense, net	$ 54	$ 28	$ 162	$ 158