Property, Plant and Equipment - Summary of property, plant and equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	$ 26,631	$ 26,346
Less accumulated depreciation	(16,748)	(16,409)
Total property, plant and equipment	9,883	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	10,138	10,422
Machinery, equipment and tooling
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	16,151	15,826
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	$ 335	$ 77