Property, Plant and Equipment - Summary of property, plant and equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 31,408	$ 30,062
Less accumulated depreciation and amortization	(18,744)	(18,187)
Total property, plant and equipment	12,664	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	10,563	10,452
Machinery, equipment and tooling
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	19,348	18,345
Construction in progress (CIP)
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 1,490	$ 1,258