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Inventories (Details) - USD ($)
Dec. 31, 2020
Dec. 31, 2019
Inventories    
Raw materials $ 24,738,000 $ 20,677,000
Work in process 24,215,000 24,946,000
Finished goods 2,562,000 3,529,000
Inventories, Total 51,515,000 49,152,000
Inventory reserve 17,700,000 16,400,000
Excess and obsolete inventory $ 162,000 $ 91,000