Property, Plant and Equipment - Summary of property, plant and equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	$ 32,778	$ 32,710
Less accumulated depreciation and amortization	(21,730)	(20,693)
Total property, plant and equipment	11,048	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	21,193	21,146
Construction in progress (CIP)
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	$ 215	$ 198