Property, Plant and Equipment - Summary of property, plant and equipment (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	$ 22,007	$ 21,130
Less accumulated depreciation and amortization	(14,603)	(14,270)
Total property, plant and equipment	7,404	6,860
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	21	21
Buildings
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	7,851	7,851
Machinery, equipment and tooling
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Gross	$ 14,135	$ 13,258