Foreign Operations - Net Sales to External Customers by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Schedule of Revenues from Geographical Segments [Line Items]
Net sales	$ 182,717	$ 175,652	$ 509,938	$ 514,638
United States
Schedule of Revenues from Geographical Segments [Line Items]
Net sales	84,756	85,762	243,801	253,259
Asia (excluding the PRC)
Schedule of Revenues from Geographical Segments [Line Items]
Net sales	36,888	26,113	91,755	77,679
People's Republic of China (PRC)
Schedule of Revenues from Geographical Segments [Line Items]
Net sales	28,108	23,437	68,852	61,015
Europe
Schedule of Revenues from Geographical Segments [Line Items]
Net sales	18,785	18,877	58,245	56,041
Latin America
Schedule of Revenues from Geographical Segments [Line Items]
Net sales	6,411	13,567	23,077	44,593
Other
Schedule of Revenues from Geographical Segments [Line Items]
Net sales	$ 7,769	$ 7,896	$ 24,208	$ 22,051