Segment Reporting - Net Sales to External Customers Based Upon Geographic Location (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Geographic Reporting Disclosure [Line Items]
Net sales to external customers	$ 106,423	$ 90,250	$ 82,682	$ 81,562	$ 91,698	$ 79,600	$ 78,538	$ 75,748	$ 360,917	$ 325,584	$ 317,548
United States
Geographic Reporting Disclosure [Line Items]
Net sales to external customers									141,595	133,924	131,670
Americas-Other
Geographic Reporting Disclosure [Line Items]
Net sales to external customers									13,531	11,815	11,718
Germany
Geographic Reporting Disclosure [Line Items]
Net sales to external customers									49,860	44,041	41,151
Europe-Other
Geographic Reporting Disclosure [Line Items]
Net sales to external customers									65,201	57,710	62,032
Japan
Geographic Reporting Disclosure [Line Items]
Net sales to external customers									35,270	32,530	24,018
Asia-Other
Geographic Reporting Disclosure [Line Items]
Net sales to external customers									$ 55,460	$ 45,564	$ 46,959