Property, Plant and Equipment - Summary of property, plant and equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 28,209	$ 26,346
Less accumulated depreciation and amortization	(17,188)	(16,409)
Total property, plant and equipment	11,021	9,937
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	7	21
Buildings
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	10,288	10,422
Less accumulated depreciation and amortization	(3,598)	(3,472)
Machinery, equipment and tooling
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	17,249	15,826
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 665	$ 77