Segment Reporting - Net Sales to External Customers Based Upon Geographic Location (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Geographic Reporting Disclosure [Line Items]
Net sales to external customers	$ 112,844	$ 99,705	$ 98,244	$ 92,834	$ 106,423	$ 90,250	$ 82,682	$ 81,562	$ 403,627	$ 360,917	$ 325,584
United States
Geographic Reporting Disclosure [Line Items]
Net sales to external customers									156,242	141,595	133,924
Americas-Other
Geographic Reporting Disclosure [Line Items]
Net sales to external customers									15,086	13,531	11,815
Germany
Geographic Reporting Disclosure [Line Items]
Net sales to external customers									53,251	49,860	44,041
Europe-Other
Geographic Reporting Disclosure [Line Items]
Net sales to external customers									74,010	65,201	57,710
Japan
Geographic Reporting Disclosure [Line Items]
Net sales to external customers									37,607	35,270	32,530
Asia-Other
Geographic Reporting Disclosure [Line Items]
Net sales to external customers									$ 67,431	$ 55,460	$ 45,564