Property, Plant and Equipment - Summary of property, plant and equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	$ 30,702	$ 30,062
Less accumulated depreciation and amortization	(18,459)	(18,187)
Total property, plant and equipment	12,243	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	10,515	10,452
Machinery, equipment and tooling
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	18,802	18,345
Construction in progress (CIP)
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	$ 1,378	$ 1,258