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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Domestic Plans | Pension Plans
Net periodic benefit cost:
Service cost	$ 16	$ 33	$ 31	$ 35
Interest cost	223	200	437	387
Expected return on plan assets	(5)	(45)	(39)	(80)
Recognized net actuarial loss	100	124	206	246
Net periodic benefit cost	334	312	635	588
Domestic Plans | Postretirement Benefit Plans
Net periodic benefit cost:
Service cost	15	32	35	56
Interest cost	126	114	250	208
Amortization of prior service credit	(47)	(19)	(94)	(103)
Recognized net actuarial loss	50	65	127	117
Net periodic benefit cost	144	192	318	278
Foreign Pension Plans
Net periodic benefit cost:
Service cost	101	138	202	280
Interest cost	93	91	188	183
Expected return on plan assets	(121)	(126)	(243)	(256)
Recognized net actuarial loss	37	39	73	80
Net periodic benefit cost	$ 110	$ 142	$ 220	$ 287