Property, Plant and Equipment - Summary of property, plant and equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	$ 32,724	$ 32,710
Less accumulated depreciation and amortization	(21,404)	(20,693)
Total property, plant and equipment	11,320	12,017
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	11,363	11,359
Machinery, equipment and tooling
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	21,187	21,146
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	$ 167	$ 198