Property, Plant and Equipment - Summary of property, plant and equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	$ 31,583	$ 30,062
Less accumulated depreciation and amortization	(19,036)	(18,187)
Total inventories	12,547	11,875
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	7	7
Buildings
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	10,594	10,452
Machinery, equipment and tooling
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	20,385	18,345
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	$ 597	$ 1,258