4. Property, Plant and Equipment, net (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Property and equipment, gross	$ 52,960	$ 52,969
Less accumulated depreciation	(31,946)	(31,921)
Total property and equipment	20,744	21,048
Land [Member]
Property and equipment, gross	1,565	1,565
Buildings And improvements [Member]
Property and equipment, gross	17,182	17,834
Machinery And Equipment [Member]
Property and equipment, gross	31,716	31,707
Vehicles [Member]
Property and equipment, gross	778	778
Office Equipment [Member]
Property and equipment, gross	862	857
Construction In Progress [Member]
Property and equipment, gross	$ 587	$ 228

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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