Pension and Postretirement Benefits - Components of Net Periodic Benefit Cost of Pension and Postretirement Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Domestic Plans | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 33	$ 39	$ 35	$ 48
Interest cost	200	178	387	407
Expected return on plan assets	(45)	(68)	(80)	(107)
Recognized net actuarial loss	124	94	246	230
Net periodic benefit cost	312	243	588	578
Domestic Plans | Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	32	17	56	47
Interest cost	114	93	208	219
Amortization of prior service credit	(19)	(105)	(103)	(216)
Recognized net actuarial loss	65	20	117	120
Net periodic benefit cost	192	25	278	170
Foreign Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	138	128	280	258
Interest cost	91	113	183	226
Expected return on plan assets	(126)	(146)	(256)	(294)
Recognized net actuarial loss	39	45	80	89
Net periodic benefit cost	$ 142	$ 140	$ 287	$ 279