4. Property, Plant and Equipment, net (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Leasehold improvements	$ 727	$ 732
Machinery and equipment	11,971	12,430
Gross property, plant, and equipment	12,698	13,162
Less accumulated depreciation and amortization	(9,132)	(9,198)
Property, plant and equipment, net	$ 3,566	$ 3,964

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount before accumulated depreciation of additions or improvements to assets held under a lease arrangement.

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Amount before accumulated depreciation of tangible personal property used to produce goods and services, including, but is not limited to, tools, dies and molds, computer and office equipment.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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